|
ScienceWeek
SCIENCE-WEEK - April 5, 2002 - Vol. 6 Number 14
An Email Research Digest Published Weekly Since 1997
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
--------------------------------------------------
But he who has been earnest in the love of knowledge
and of true wisdom, and has exercised his intellect
more than any other part of him, must have thoughts
immortal and divine, if he attain truth, and in so far
as human nature is capable of sharing in immortality,
he must altogether be immortal.
-- Plato (428-348 BC)
--------------------------------------------------
=-=-=-=-=-=-=-=-=
Section 1
=-=-=-=-=-=-=-=-=
Contents of this Issue (Full reports in Section 2):
[(*) = includes background reports]
Basic Sciences
--------------
1. Artificial Membrane Receptors and Ion Channels
2. Involvement of Water in Carbohydrate-Protein Binding (*)
3. On Hedgehog Proteins
4. On Fast vs. Slow Synaptic Transmission (*)
5. Visual Perception and Transcranial Magnetic Stimulation
6. Protein Domains and Repeats
7. On Beta-Sheets in Proteins
8. On Dust Plasmas
9. Foldamers: Synthetic Macromolecules vs. Biomacromolecules
10. Galaxy Clusters and Supernova Heating in the Early Universe
11. Organic Coatings of Mineral Surfaces: Biofilms
12. On Rotating Black Holes
Praxis
------
13. Pathogenesis of River Blindness
14. On Childhood Obesity (*)
15. Retinal Implants and Restoration of Vision
16. On Postpartum Depression
17. Fitness and Survival
18. Cochlear Implants and Other Hearing Devices
19. On Chemisorbate Bonding
20. Gas Hydrates and Geochemical Carbon Dioxide Storage
21. Soil Fertility and Hunger in Africa
22. On Health of the Global Poor (*)
23. Imaging the Structures of Nanomaterials
24. On Ultrathin Polymer Films at Interfaces (*)
Miscellany
----------
25. In Focus: On Human Speech
26. SW Archive:
Science in the Next 50 Years: Which Questions? What Answers?
=-=-=-=-=-=-=-=-=
Section 2
=-=-=-=-=-=-=-=-=
1. ON ARTIFICIAL MEMBRANE RECEPTORS AND ION CHANNELS
S. Futaki et al (Kyoto University, JP) discuss artificial
receptors and ion channels, the authors making the following
points:
1) Natural receptor proteins and ion channel proteins serve
in the transduction of biological signals across cell membranes.
These molecules are often constructed by the association of
multiple homologous subunits to yield an organized structure.
Interaction of a specific ligand may then induce a conformational
switch to transmit specific ions in the cells as biological
signals.
2) Preserving the features of natural receptor proteins in
simplified peptide-based systems is a challenge in peptide
engineering offering potential for creating novel molecular
devices and channel protein models. Amphiphilic helical peptides
derived from transmembrane segments of natural ion channel
proteins and from artificial design have been shown to self-
assemble in membranes to form channels. For example, the assembly
of a mere approximately 20-amino-acid-residue peptide can
manifest a fundamental function of ion channel proteins, even
though the natural proteins are often composed of more than 1000
amino acids.
3) Self-assembly of channel peptides often produces a
channel of multiple open states, where the difference in the
association number (or the association state) may be detected as
a difference in channel conductance levels. To control the
association number of channel peptides, template molecules have
been effectively employed. The application of natural pore-
forming membrane proteins and non-peptide based molecules as
frameworks for the construction of artificial ion channels is
potentially a means for making designed channel pores, as well as
a means to create ion channels in which the ion flux can be
controlled by external stimuli such as binding of specific
ligands and changes in the electrical transmembrane potential.
4) The authors describe an experimental model ion channel
system involving the peptide antibiotic alamethicin with extra-
membrane control of channel peptide assembly, and the system
exhibiting channel current modulation.
-----------
J. Am. Chem. Soc. 2001 123:12127
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
2. INVOLVEMENT OF WATER IN CARBOHYDRATE-PROTEIN BINDING
The "lectins" are a group of sugar-binding proteins of non-
immune system origin which agglutinate cells and/or precipitate
glycoconjugates. Lectins are widely distributed in nature, found
in seeds and other parts of certain plants, and are also found in
other organisms ranging from bacteria to mammals.
... ... C. Clarke et al (Complex Carbohydrate Research Cntr., US)
discuss carbohydrate-protein binding, the authors making the
following points:
1) Although interactions involving nucleic acids and
proteins are fundamental to biology and have been intensively
studied, the importance of recognition processes involving
carbohydrates is only recently gaining attention. Protein-
carbohydrate interactions are implicated in embryogenesis,
fertilization, neuronal development, and hormonal activities, as
well as in cell proliferation and cell organization into specific
tissues. These interactions are also important in health science
and are involved in the invasion and attachment of pathogens,
inflammation, metastasis, blood group immunology, and
xenotransplantation. Among protein-carbohydrate complexes, those
involving lectins are of considerable interest because the high
specificities of these interactions have led to the use of
lectins as molecular probes.
2) Lectin-carbohydrate structures have been widely studied,
but the thermodynamics of these interactions are complex and
poorly understood. While counter-examples exist, protein-
carbohydrate associations are typified by favorable enthalpic
terms that are offset by unfavorable entropic contributions.
Generally, only a few hydroxyl groups of an oligosaccharide serve
critical roles in determining the binding affinity and
specificity. These key binding hydroxyl groups are arranged in
clusters presented by different monosaccharide units. This type
of spatial grouping provides a very effective mechanism for
establishing high levels of fidelity in physiological processes
guided by protein-oligosaccharide recognition. Key polar groups
have been identified in studies with synthetic analogues in which
hydroxyl groups were systematically replaced by either halogen or
hydrogen atoms, and these deoxy analogues displayed significant
loss of affinity.
-----------
J. Am. Chem. Soc. 2001 123:12238
----------
Related Background:
COMMUNICATION BETWEEN NON-CONTACTING MACROMOLECULES
J. Voelker et al (State University of New Jersey Rutgers, US)
report a quantitative experimental demonstration of solvent-
mediated communication between noncontacting polymers. The
authors show that changes in the activity of a solvent component
caused by a conformational change in one biopolymer can result in
changes in the physical properties of a second noncontacting
biopolymer present in solution. Specifically, the release of
protons on denaturation of a donor polymer (a 4-stranded DNA
tetraplex) modulates the melting temperature of a non-contacting
accepting polymer (polyadenylate). In addition to such cross-
talk, the authors also demonstrate counter-ion mediated cross-
talk between non-contacting biopolymers. The authors demonstrate
that such "through-solvent" dialogue between biopolymers that do
not directly interact can be used to evaluate association-
dissociation reactions of solvent components (e.g., protons,
sodium ions) with one of the two biopolymers. The authors propose
that such through-solution dialogue is a general property of all
biopolymers, and that as a result, such solvent-mediated cross
talk should be considered when assessing when assessing reactions
of multicomponent systems such as those that exist in essentially
all biological processes.
-----------
Proc. Nat. Acad. Sci. 2001 98:7694
-----------
Related Background:
ON WATER AND THE STRUCTURES OF BIOLOGICAL MOLECULES
A prominent consideration in the minds of biologists who work at
the level of cells and molecules is that water is the most
prevalent chemical substance in all biological systems, and that
interactions of water with other biological molecules,
particularly with biological macromolecules, are not clearly
understood but are probably of considerable significance.
... ... M. Gerstein and M. Levitt present a review of some
aspects of the physical chemistry of water and an account of
their own computer simulations of biological macromolecules in
aqueous solutions. The authors make the following points: 1) At
the present time it is possible to model proteins and their
associated water molecules on a desktop computer in a few days.
Researchers have now simulated the aqueous structures of more
than 50 proteins and nucleic acids. 2) A single water molecule
has an essentially tetrahedral geometry, with an oxygen atom at
the center of the tetrahedron, hydrogen atoms at 2 of the 4
corners, and clouds of negative charges at the other 2 corners.
Reflecting the tetrahedral geometry of water, each molecule in
liquid water often forms 4 hydrogen bonds: 2 hydrogen bonds
between its hydrogens and the oxygen atoms of 2 other water
molecules, and 2 hydrogen bonds between its oxygen atom and the
hydrogens of other water molecules. The necessity of maintaining
a tetrahedral hydrogen-bonded structure gives water an "open"
loosely packed structure compared with that of most other liquids
[*Note #1]. 3) Present computer simulations are able to reproduce
quantitatively many of the bulk properties of water, such as its
average structure, rate of diffusion, and *heat of vaporization.
4) Biological molecules such as proteins and DNA contain both
hydrophilic and hydrophobic parts arranged in long chains. The 3-
dimensional structures of these molecules are determined by the
way these chains fold into more compact arrangements in which
hydrophilic groups are on the surface where they can interact
with water and hydrophobic groups are buried in the interior away
from water. These local macromolecule solubility considerations
were formulated in 1959 by Walter Kauzman as a "hydrophobic
effect" crucial for protein folding. 4) There are 3 types of
water molecules that must be considered in a computer model of a
biological molecule in aqueous solution: a) the ordered water
surrounding and strongly interacting with the macromolecule; b)
the bulk water beyond the ordered water; and, c) any water
molecules that may be buried within the macromolecule. 5)
Computer simulations of DNA in water have revealed that water
molecules are able to interact with nearly every part of the
double helix of DNA, including the nucleotide base pairs that
constitute the genetic code. In contrast, water is not able to
penetrate deeply into the structure of proteins, whose
hydrophobic regions are arranged on the inside into a close-
fitting core [*Note #2].
-----------
Scientific American 1998 November
-----------
Notes:
... ... *Note #1: In hydrated crystal structures, water molecules
generally donate two hydrogen bonds but may accept either one or
two. When water molecules are 3-coordinated (rather than 4-
coordinated as discussed by the authors in their review), the
geometry can be planar or pyramidal. But examples are known of
coordination as low as 2 and as large as 7.
... ... *heat of vaporization: The quantity of energy required to
evaporate 1 mole (or a unit mass) of a liquid at constant
pressure and temperature.
... ... *Note #2: Concerning the interaction of water molecules
with biological molecules, water molecules hydrogen-bonded to the
functional groups of biological molecules are apparently linked
in chains into extended networks, and some researchers have
suggested the *polarizability of these networks provides a
mechanism for long-range recognition between biological molecules
in aqueous solution.
... ... *polarizability: The electric dipole moment induced in a
system (such as an atom or molecule) by an electric field of unit
strength.
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
3. ON HEDGEHOG PROTEINS
A "hedgehog protein" is a transmembrane protein involved in
segment polarity and cell-cell signaling during embryogenesis and
metamorphosis in the fruit fly Drosophila melanogaster, and in
other insects and vertebrates.
... ... P.W. Ingham and A.P. McMahon (University of Sheffield,
UK) discuss hedgehog proteins, the authors making the following
points:
1) Since their isolation in the early 1990s, members of the
hedgehog family of intercellular signaling proteins have come to
be recognized as key mediators of many fundamental processes in
embryonic development. The activities of these proteins are
central to the growth, patterning, and morphogenesis of many
different regions within the body plans of vertebrates and
insects, and most likely other invertebrates. In some contexts,
hedgehog signals act as morphogens in the dose-dependent
induction of distinct cell fates within a target field, in others
as mitogens regulating cell proliferation, or as inducing factors
controlling the form of a developing organ. These diverse
functions of hedgehog proteins raise many intriguing questions
about their mode of operation. For example, how do these proteins
move between or across fields of cells? How are their activities
modulated or transduced? What are their intracellular targets?
2) Embryological studies over much of the last century that
relied primarily on the physical manipulation of cells within the
developing embryo or within fragments of the embryo in culture,
provided many compelling examples of the primacy of cell-cell
interactions in regulating invertebrate and vertebrate
development. The subsequent identification of many of the
signaling factors that mediate cellular communication has led to
two general conclusions: a) Although there are many important
signals, most of these fall into a few large families of secreted
peptide factors. b) Parallel studies in invertebrate and
vertebrate systems have demonstrated that although the final
outcome might look quite different (e.g., a fly versus a mouse),
there is a striking evolutionary conservation in the deployment
of members of the same signaling families to regulate development
of these seemingly quite different organisms. One of the most
intriguing examples of this phenomenon is the hedgehog family of
proteins.
-----------
Genes & Development 2001 15:3059
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4. ON FAST VS. SLOW SYNAPTIC TRANSMISSION AND NEUROTRANSMITTERS
Paul Greengard (The Rockefeller University, US) discusses
synaptic transmission, the author making the following points:
1) The current consensus is that there are two categories of
chemical transmission between nerve cells, referred to as "fast"
and "slow" synaptic transmission. Approximately half of the fast
synapses in the brain are excitatory, and most of these fast
excitatory synapses use glutamate as their neurotransmitter. The
other half of the fast synapses are inhibitory, and most of fast
inhibitory synapses use gamma-amino-butyric acid (GABA) as their
neurotransmitter. Synaptic transmission at fast synapses occurs
in less than 1 millisecond and is attributed to the ability of
the fast-acting neurotransmitters to open ligand-operated ion
channels present in the plasma membrane of the postsynaptic
cells. In fast excitatory transmission, glutamate binds to a
receptor, causing a change in the conformation of the receptor,
which allows positively charge sodium ions to rush into the cell
and cause a depolarizing (i.e., excitatory) signal to be
generated in the target cell. In fast inhibitory transmission,
GABA binds to its receptor, causing a change in the conformation
of the receptor, which allows negatively charged chloride ions to
permeate the cell and cause a hyperpolarizing (i.e., inhibitory)
signal to be generated in the target cell.
2) The second type of communication between nerve cells,
"slow synaptic transmission", occurs over periods of hundreds of
milliseconds to minutes, and is enormously more complex than fast
synaptic transmission. At least 100 compounds, which can be
grouped into 3 chemical classes, namely biogenic amines,
peptides, and amino acids, are now believed to serve as
neurotransmitters in the brain, and the vast majority of these
apparent neurotransmitters appear to work through slow synaptic
transmission. Thus, it seems likely that all of the biogenic
amines and all of the peptide neurotransmitters produce their
effects on their target cells through slow synaptic transmission.
In addition, even the fast-acting neurotransmitters, including
the amino acids glutamate and GABA, produce many of their effects
through slow synaptic transmission pathways.
-----------
Science 2001 294:1025
----------
Related Background:
NEUROBIOLOGY: ON THE STABILITY OF FAST-SYNAPSE RECEPTORS
In neurobiology, the term "axon" refers to the long extensions of
neurons that propagate electrical activity (action potentials) to
other cells, and the term "synapse" refers to a functional
junction between one neuron and another neuron or between a
neuron and another type of cell (e.g., a muscle cell). The
general paradigm is that electrical activity in neuron (A)
provokes a response in cell (B); the (A) side of the junction is
called "presynaptic" and the (B) side of the junction is called
"postsynaptic". In mammalian nervous systems, the major event at
nearly all synapses is the release of a neurotransmitter
substance by the presynaptic contact (the terminal of the axon of
the input neuron), the neurotransmitter interacting with specific
membrane molecular receptors associated with the postsynaptic
contact. At the nerve-muscle junctions (neuromuscular junctions)
in the "voluntary" fast-response muscle systems, the
neurotransmitter substance is usually acetylcholine, the
transmitter substance released into junctions of relatively
complicated micron-scale architecture ("muscle endplates"). In
general, in mammals, the system is one which has evolved to make
possible rapid activation of important fast-responding muscle
systems, with stringent controls over the range and dynamics of
excitation of these muscle systems by their input.
... ... Miriam M. Salpeter (Cornell University, US) presents a
commentary on some current research concerning "fast synapses",
the author making the following points:
1) In synapses that must generate action potentials within
microseconds of neurotransmitter release (fast synapses), the
receptors need to be clustered in the postsynaptic membrane at
high density and close to where the neurotransmitter is released.
The neuromuscular junction has just such an organization. The
principal transmitter at the neuromuscular junction is
acetylcholine, which is released from the presynaptic nerve
terminal within 50 nanometers of the postsynaptic muscle membrane
that contains densely arrayed acetylcholine receptors --
approximately 10^(4) receptors per square micron.
2) At such a junction, there is a steady turnover of
acetylcholine receptors, with newly synthesized receptors
replacing those that are periodically degraded and internalized
(i.e., withdrawn into the cell interior). Both the location on
the muscle membrane where the acetylcholine receptors are
internalized, as well as the regulatory mechanisms involved, have
not yet been determined.
3) In recent experiments, Akaaboune et al (see below)
observed individual neuromuscular junctions and studied these
repeatedly over time. These experiments demonstrate that the
muscle membrane surrounding the neuromuscular junction
(perijunctional membrane) is involved in receptor turnover, and
that muscle contraction is essential for regulating acetylcholine
receptor degradation.
... ... In the same issue of the journal, Akaaboune et al
(Washington University St. Louis, US) report the following:
1) Quantitative *fluorescence imaging was used to study the
regulation of acetylcholine receptor number and density at
neuromuscular junctions in living adult mice. At fully functional
synapses, these receptors have a half-life of approximately 14
days. However, 2 hours after neurotransmission was
pharmacologically blocked (by the agent bungarotoxin), the half-
life of these receptors was reduced to less than 1 day, with a
degradation rate 25 times faster than normal. Most of the lost
receptors were not quickly replaced. Direct muscle stimulation or
restoration of synaptic transmission inhibited this rapid
degradation process.
2) Receptors removed by the degradation process from
nonfunctional synapses persisted for hours in the perijunctional
membrane before being locally internalized. Dispersed receptors
could also reaggregate at the junction once neurotransmission was
restored. The authors suggest that the rapid and reversible
alteration in neurotransmitter receptor density at the
neuromuscular junction in vivo may parallel changes believed to
occur in the central nervous system at synapses undergoing
*potentiation and *depression, and that this observed dependence
of neurotransmitter receptor density on activity in the
neuromuscular junction has important implications for clinical
aspects of diseases of such junctions.
-----------
Science 1999 286:424,503
-----------
Notes:
... ... *fluorescence imaging: The technique in these experiments
involved the use of tetramethyl-rhodamine-labeled alpha-
bungarotoxin and the assay of localized fluorescence intensity
with time. The term "bungarotoxin" refers to a group of
neurotoxins derived from the venom of the krait snake Bungarus
multicinctus. Alpha-bungarotoxin is a single polypeptide chain of
74 amino acid residues, the molecule known to bind to muscle
endplate acetylcholine receptors and cause paralysis by
preventing synaptic activation. (The krait snake belongs to the
group Elapidae: cobras, mambas, kraits, coral snakes.)
... ... *potentiation: In this context, in general, an increase
in the effects of synaptic input.
... ... *depression: In this context, in general, a decrease in
the effects of synaptic input.
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
5. ON VISUAL PERCEPTION AND TRANSCRANIAL MAGNETIC STIMULATION
S. Shimojo et al (California Institute of Technology, US) discuss
visual perception, the authors making the following points:
1) Research during the past 40 years has revealed that there
are approximately 30 different visual areas in the primate brain,
and that within these areas there are parallel streams of
processing and distinct modules. But how is neuronal activity in
the various areas related to our conscious visual perception? How
can our unitary visual experience be based on neural activity
spread across distinct streams of processing in multiple brain
areas? The answers to these questions have profound implications
for our understanding of the relationship between mind and brain.
Whereas early pioneering work focused on the delineation of
visual areas in the brain and the basic response properties of
neurons, recent research attempts to expose the roles different
areas play in perception and the extent to which there are
hierarchies of visual computations in the brain.
2) Conscious visual experience is thought to be based on
activity in visual areas ("early cortical structures") of
cerebral cortex that receive input from the retina. Early
cortical structures are organized topographically with regard to
the visual world, and this topography can be exploited to
investigate the role of different visual areas in perception. For
example, neuronal activity in visual cortex can be locally
blocked by transcranial magnetic stimulation, and the effect on
visual perception in the corresponding portion of the visual
field can be assessed. Kamitani and Shimojo (1999) briefly (40 to
80 milliseconds) presented a large grid pattern to human
observers, and after a delay of 80 to 170 milliseconds, a single
pulse of transcranial magnetic stimulation was applied to the
occipital lobe. The transcranial magnetic stimulation caused the
observers to perceive a disk-shaped patch of homogeneous color in
the visual field on the opposite side from the side of the brain
receiving transcranial magnetic stimulation (TMS-induced
scotoma). When the visual stimulus was a grating composed of
parallel lines rather than a rectilinear grid, the scotoma was
distorted and appeared to be an ellipse with its short axis along
the contours. This contour-dependent distortion appears to
reflect long-range interactions between neurons selectively
responsive to similar orientations.
-----------
Proc. Nat. Acad. Sci. 2001 98:12340
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
6. ON PROTEIN DOMAINS AND REPEATS
C.P. Ponting et al (University of Oxford, UK) discuss protein
domains and repeats, the authors making the following points:
1) "Protein domains" are regions of a protein that form
compact 3-dimensional structures, and which often evolve
independently of one another. Internal duplication within genes
appears to have been a prominent evolutionary mechanism for
creating functional innovation, giving rise to multiple domains
or "repeats" within the same polypeptide. (Domains are
distinguished from repeats in that a domain occurs singly in at
least one protein.) The discovery of proteins with internal
repeats has often been crucial for the detection of a novel
homologous family. For example, the realization that pleckstrin
contained a domain duplication provided the necessary impetus for
the discovery of the pleckstrin homology domain family.
Similarly, the identification of WD40-like repeats in beta
subunits of G-proteins preceded extensive investigations into
their structures and functions.
2) To date, identification of domain and repeat families has
depended almost exclusively on sequence comparison of single
proteins with nonredundant databases, or all-against-all
comparisons of protein sequence sets. Families that have hitherto
escaped detection are expected to represent short and/or weakly
conserved sequences with similarity scores lying close to
background. The background level of similarity encountered in a
search is governed by the most statistically significant
similarity expected by chance, and depends principally in the
number of sequence comparisons made. An all-against-all
comparison of (N) proteins will have a background level P-value
N(N-1)/2 times smaller than that obtained in a single comparison.
Consequently, with the current and rapidly increasing sizes of
databases, this strategy may no longer be optimal.
-----------
Genome Research 2001 11:1996
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
7. ON BETA-SHEETS IN PROTEINS
In general, protein chains fold into alpha-helices or
beta-sheet structures. The beta-sheet is a protein structure
where the peptide is extended and stabilized by hydrogen bonding
between NH and CO groups of different polypeptide chains or of
separate regions of the same chain.
The structures of biopolymers are generally denoted as
follows: 1) Primary structure: The sequence of subunits that
comprise the macromolecule (e.g., the amino acid sequence of a
protein). 2) Secondary structure: The localized arrangement in
space of regions of a biopolymer (e.g., the alpha-helix). 3)
Tertiary structure: The 3-dimensional configuration of a
biopolymer. 4) Quaternary structure: The 3- dimensional
arrangement and constitution of a multimeric macromolecule (i.e.,
a substance containing more than one biopolymer; an entity
consisting of biopolymer subunits.
... ... S.T. Phillips et al (University of California Berkeley,
US) discuss beta-sheets, the authors making the following points:
1) Local conformation within proteins and peptides is
largely described by secondary structural elements, such as
alpha-helices, beta-turns, and beta-strands, which determine the
3-dimensional orientation of the amino acid side chains and
thereby the longer range interstrand and intermolecular
interactions.
2) Beta-strands, and beta-sheets derived from them, play
important roles in protein-protein interactions and in the
association of proteins with other biopolymers such as nucleic
acids. The beta-sheet-like association and precipitation of
hydrophobic protein fragments in amyloid plaques is strongly
implicated in neurodegenerative diseases. Despite its ubiquity,
the fully extended beta-strand conformation is typically a minor
component of the dynamic equilibrium for an oligopeptide outside
the context of a folded protein structure, in which the hydrogen-
bonded network of a beta-sheet provides a stabilizing template.
3) Short beta-sheets are known only as insoluble aggregates,
and peptides designed to exist in monomeric all-beta-sheet form
contain at least 20 amino acids. A variety of small-molecule
beta-sheet templates have been described, which either juxtapose
two peptide strands in the antiparallel orientation or which
provide an extended array of hydrogen-bonding sites via a beta-
turn linkage.
-----------
J. Am. Chem. Soc. 2002 124:58
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
8. ON DUST PLASMAS
G.A. Hebner et al (Sandia National Laboratories, US) discuss dust
particle plasmas, the authors making the following points:
1) Plasmas containing dust particles occur in systems as
diverse as interstellar space dust and microelectronics
processing discharges. Under appropriate conditions, first
identified in 1994, the dust particles will assemble into a
crystalline structure. Since those first observations,
experiments and theoretical analyses have examined interaction
mechanisms and collective properties. In a more general view,
plasma dust crystals are a subset of broader research efforts to
understand the structure and dynamics of charged particle
assemblies. Examples of such systems range from laser-cooled ions
confined by traps to colloids trapped between glass plates.
2) Most plasma dust experiments are performed using micron-
sized particles in radio-frequency-excited parallel-plate
discharges. In the plasma, injected dust particles charge
negatively and form a levitated layer of particles above the
lower electrode at the point where the electrostatic forces
produced by the electrode plasma sheath are counterbalanced by
gravity. The horizontal confining forces are many orders of
magnitude weaker than the vertical confining forces, and thus a
knowledge of the radial confining forces is critical in
determining the properties of the resulting 2-dimensional
crystal.
3) The authors report the use of a curved electrode with a
spherical radius of curvature to provide a well-characterized
transverse confining force (pressure) on such 2-dimensional
plasma crystals, and present an analysis of the compression of
the 2-dimensional layer subjected to this pressure in order to
determine the constitutive interaction of the particles. The
authors provide a photograph of a 14-millimeter-diameter single-
layer plasma crystal containing 434 particles formed above the
parabolic well in the lower electrode of the experimental setup.
-----------
Phys. Rev. Lett. 200187:235001
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
9. FOLDAMERS: SYNTHETIC MACROMOLECULES VS. BIOMACROMOLECULES
D.J. Hill et al (University of Illinois Urbana-Champaign, US)
discuss macromolecules, the authors making the following points:
1) The breadth of structure and function displayed by the
molecules of biology is remarkable. Considering that there are
only 3 major biopolymer backbones (proteins, ribonucleic acids,
and polysaccharides), nature demonstrates that copolymer sequence
is a powerful way to meet diverse chemical challenges. A logical
question is whether biomacromolecule building blocks are unique
in their suitability for life. Systematic studies on alternative
monomers closely related to those found in nature have provided
clues concerning the fitness of alpha-amino acids, ribofuranosyl
(5'->3') nucleic acids, and phosphodiester linkages. But the
question why nature is such and not otherwise continues to be
unresolved. Looking beyond biopolymers and their related
derivatives, it is possible to imagine that other chain molecules
are capable of similar functions.
2) Most of the interesting functions carried out by
biomacromolecules, such as molecular recognition, information
storage, and catalysis, involve stable and compact solution
structures that approach conformational uniqueness. These high
molecular weight macromolecules might be described as glassy-like
nanometer-sized particles that are suspended in solution and that
consist of one to at most a few polymer chains. The spatial
position of most of the backbone atoms is fixed, except for minor
fluctuations about their equilibrium coordinates. There is also a
congruency between particles having identical or even similar
sequences. The surface of these particles includes 3-dimensional
molecular-sized crevices lined with information-rich surfaces,
and it is from here that affinity, specificity, and catalytic
activity spring forth. Reasoning by analogy, the quest for
function in synthetic polymer chains should thus be closely tied
to the invention of new polymer molecules that acquire ordered
solution structures. Chemists have endeavored to intentionally
generate unnatural oligomeric sequences that take on well-defined
conformations in solution, and this subject has come to be known
as the field of "foldamers".
3) The authors specifically define a foldamer as any
oligomer that folds into a conformationally ordered state in
solution, the structures of which are stabilized by a collection
of noncovalent interactions between nonadjacent monomer units.
The authors distinguish two major classes of foldamers: a)
single-stranded foldamers that only fold (e.g., peptidomimetics
and their abiotic analogues); b) multiple-stranded foldamers that
both associate and fold (e.g., nucleotidomimetics and their
abiotic analogues).
-----------
Chem Revs. 2001 101:3893
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
10. GALAXY CLUSTERS AND SUPERNOVA HEATING IN THE EARLY UNIVERSE
Contemporary cosmology distinguishes two kinds of matter,
"ordinary matter" and "dark matter". In general, a baryon is a
nuclear particle (e.g., a proton) built from 3 quarks
(fundamental particles that combine to make up protons, neutrons,
and mesons), and so-called "ordinary matter" is baryonic. In this
context, the term "dark matter" refers to material whose presence
can be inferred from its effects on the motions of stars and
galaxies, but which cannot be seen directly because it emits
little or no radiation. It is believed that as much as 90 percent
of the mass in the Universe may exist as some form or dark
matter, although the proposed percentage of dark matter varies
widely with different cosmological models.
The term "supernova" refers to a class of violently
exploding stars whose luminosity after eruption suddenly
increases millions or billions of times its normal level, the
supernova explosion a cataclysmic event associated with the
essential end of the active (energy-generating) life of the star.
... ... G.M Voit and G.L. Bryan (Space Telescope Science
Institute, US) discuss galaxy clusters, the authors making the
following points:
1) Clusters of galaxies are believed to contain
approximately 10 times as much dark matter as baryonic matter.
The dark component therefore dominates the gravitational
potential of a cluster, and the baryons confined by this
potential radiate x-rays with a luminosity that depends mainly on
the gas density in the core of the cluster.
2) Predictions of the properties of these x-rays based on
models of cluster formation do not, however, agree with
observations. If the models ignore the condensation of cooling
gas into stars and also ignore feedback from the associated
supernovae, the models overestimate the x-ray luminosity because
the simulated density of the core gas is too high. An early
episode of uniformly distributed supernova feedback could rectify
this by heating the uncondensed gas and therefore making it more
difficult for the gas to compress into the core. But such a
process seems to require an implausibly large number of
supernovae.
3) The authors demonstrate how radiative cooling of
intergalactic gas and subsequent supernova heating combine to
eliminate highly-compressible low-entropy gas from the
intracluster medium. This brings the galaxy cluster core entropy
and x-ray luminosities of clusters into agreement with
observations in a way that depends little on the efficiency of
supernova heating in the early Universe.
-----------
Nature 2001 414:425
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
11. ORGANIC COATINGS OF MINERAL SURFACES: BIOFILMS
In general, the term "passivation" refers to the reaction of a
solid with another substance in a way such that a protective
layer forms on the surface of the solid, the layer essentially
causing the cessation of the reaction. The solid is then said to
be "passivated". An example is the reaction of a solid metal with
gaseous oxygen to form an oxide surface coat that subsequently
prevents further oxidation.
... ... A.S. Templeton et al (Stanford University, US) discuss
mineral surfaces, the authors making the following points:
1) The dissolved concentration of trace metal in terrestrial
and marine environments is directly linked to sorption and
precipitation reactions at mineral surfaces. However, various
types of natural organic matter form ubiquitous surface coatings
on minerals exposed to aqueous solutions.
2) Among the most complex and dynamic types of common
organic coatings are "biofilms". Such films form when microbial
organisms attach to a surface and produce a highly hydrated
framework of extracellular polymers in which the microorganisms
become embedded. These biofilms may have a sorptive capacity
similar in magnitude to many reactive mineral substrates, and
thus are potentially significant sinks for metals.
3) The presence of organic coatings may also alter the
reactivity of the underlying mineral surface through blocking of
high-energy surface sites or through modifying the electrical
properties of the mineral-water interface. In particular, it has
been observed that bacterial cells often preferentially attach to
surface features such as scratches, pits, cleavage steps, and
edges of mineral grains. Passivation of the mineral surfaces
could result if functional groups present within bacterial
surface polymers (or within the exopolysaccharide matrix) were
directly bound by a ligand-exchange mechanism to these high-
energy sites on the mineral surface. How these biofilm coatings
may alter metal ion partitioning between mineral surfaces and the
surrounding aqueous environment is largely unresolved.
-----------
Proc. Nat. Acad. Sci. 2001 98:11897
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
12. ON ROTATING BLACK HOLES
Since all black holes must have mass, there are 4 possible types
of black hole, each type derived from equations of the general
theory of relativity:
a) A "Schwarzschild black hole" (first derived 1916) has no
charge and no angular momentum.
b) A "Reissner-Nordstrom" black hole (first derived 1918)
has charge but no angular momentum.
c) A "Kerr black hole" (first derived 1963) has angular
momentum but no charge.
d) A "Kerr-Newman black hole" (first derived 1965) has both
charge and angular momentum.
It is currently believed that real black holes are almost
certainly rotating and have very little electric charge, so that
the Kerr solution should be the most applicable.
... ... M.H.van Putten and A. Levinson (Massachusetts Institute
of Technology, US) discuss rotating black holes, the authors
making the following points:
1) Gravitation is a universal force in nature, and it
ultimately leads to black holes as fundamental objects.
Supermassive black holes are believed to form the nuclei of
galaxies, and stellar-mass black hole candidates are found in
soft x-ray transients and galactic microquasars. Rotating black
holes, discovered by Kerr as exact solutions to general
relativity equations, are of great astrophysical interest because
their emissions provide a method for identifying and studying
black holes.
2) Kerr black holes build up angular momentum, and this
energy can be emitted in accord with known principles.
Spontaneous emissions in vacuo are suppressed by canonical
angular momentum barriers, but Kerr black holes -- surrounded by
a torus magnetosphere supported by surrounding matter -- do not
behave this way.
3) The authors report that the rotational energy of a black
hole surrounded by a torus is released through several channels.
They have determined that a minor fraction of the energy is
released in baryon-poor outflows from a differentially rotating
open magnetic flux tube, and a major fraction is released in
gravitational radiation by the torus. The authors associate the
energy emitted in baryon-poor outflows with gamma-ray bursts. The
remaining fraction is released in torus winds, thermal emissions,
and conceivably mega-electronvolt neutrino emissions. The emitted
gravitational radiation can be detected by gravitational wave
experiments, and this provides a method for identifying Kerr
black holes in the Universe.
-----------
Science 2002 295:1874
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
13. PATHOGENESIS OF RIVER BLINDNESS
The disease called "river blindness" (onchocerciasis) is produced
by infection with the filarial nematode worm Onchocerca volvulus,
the infection causing chronic skin disease and eye lesions that
may lead to blindness. The disease is spread by blackflies that
breed in swiftly flowing streams. Infective larvae inoculated
into the skin during the bite of a blackfly develop into adult
worms in approximately 1 year. Adult female worms may live up to
15 years in subcutaneous nodules, with adult male worms migrating
between nodules to inseminate the female worms. Approximately 18
million people worldwide are infected with this disease, of whom
approximately 270,000 are blind and approximately 500,000
visually impaired. The disease is most common in tropical and
Sahel Africa, and is also found in Yemen, southern Mexico,
Guatemala, Ecuador, Columbia, Venezuela, and the Brazilian
Amazon.
... ... A.V. Saint Andre et al (Case Western Reserve University,
US) discuss river blindness, the authors making the following
points:
1) Wolbachia bacteria are essential symbionts of the major
pathogenic filarial nematode parasites of humans, including O.
volvulus, which causes river blindness. Wolbachia are abundant in
all developmental stages of filarial nematodes, including the
hyperdermis and reproductive tissue of adult parasites. In
contrast to their relatives in arthropods, Wolbachia in filarial
nematodes appear to have evolved as an essential endosymbiont.
Antibiotic therapy in humans and experimental filarial infection
have demonstrated that embryogenesis is completely dependent on
the presence of Wolbachia.
2) The authors report that using a mouse model for river
blindness in which soluble extracts of filarial nematodes were
injected into the corneal stroma, they have demonstrated that the
predominant inflammatory response in the cornea is due to species
of endosymbiotic Wolbachia bacteria. The authors suggest their
results indicate that in addition to targeting Wolbachia for
sustained anti-filarial effects, clearance of Wolbachia by
antibiotic treatment may also reduce and prevent ocular
onchocerciasis.
-----------
Science 2002 295:1892
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
14. ON CHILDHOOD OBESITY
Albert P. Rocchini (University of Michigan, US) discusses
childhood obesity, the author making the following points:
1) Childhood obesity has reached epidemic proportions.
Worldwide, approximately 22 million children under 5 years of age
are overweight, and during the past 3 decades, the number of
overweight children in the US has more than doubled. In 1983,
18.6 percent of preschool children in the US were defined as
overweight, and 8.5 percent were defined as obese. By the year
2000, 22 percent of preschool children were overweight and 10
percent were obese. Data indicate that the prevalence of
overweight has increased by 21.5 among non-Hispanic black
children, 21.8 percent among Hispanic children, and 12.3 percent
among non-Hispanic white children. Similar increases in the
prevalence of obesity have been observed worldwide, and childhood
obesity is the most serious and prevalent nutritional disorder in
the US.
2) Obesity has a substantial effect on cardiovascular risk.
Childhood obesity is directly linked to abnormalities in blood
pressure, lipid, lipoprotein, and insulin levels in adults, as
well as to the risk of both coronary artery disease and diabetes.
It has been documented that 80 percent of obese adolescents have
elevated systolic blood pressure, diastolic blood pressure, or
both. Furthermore, 97 percent of such adolescents have 4 or more
of the following cardiovascular risk factors: elevated serum
triglyceride levels (more than 100 milligrams per deciliter), low
levels of high-density lipoprotein cholesterol, increased total
cholesterol levels (more than 200 milligrams per deciliter),
elevated systolic blood pressure, diastolic blood pressure, or
both, diminished maximal oxygen consumption, and a strong history
in the immediate family of coronary heart disease, myocardial
infarction, angina pectoris, or high blood pressure.
-----------
New Engl. J. Med. 2002 346:854
----------
Related Background:
OBESITY AND DIABETES IN THE US
A.H. Mokdad et al (NIH, US) discuss the continuing epidemics of
obesity and diabetes in the US. Obesity and diabetes are
currently major causes of morbidity and mortality in the US, and
evidence from several studies indicates that obesity and weight
gain are associated with an increased risk of diabetes. Each
year, an estimated 300,000 US adults die of causes related to
obesity. Obesity also substantially increases morbidity and
impairs quality of life, and overall, the direct costs of obesity
and physical inactivity account for approximately 9.4 percent of
US health care expenditures. The direct and indirect costs of
health care associated with diabetes in 1997 were an estimated
$98 billion. The authors report a study of the prevalence of
obesity, diabetes, and use of weight control strategies among US
adults in the year 2000. A random-digit telephone survey was
conducted in all states in the year 2000 with 184,000 adults aged
18 years or older. The body-mass index was calculated from self-
reported weight and height; also analyzed were self-reported
diabetes, prevalence of weight loss or weight maintenance
attempts, and weight control strategies used. In the year 2000,
the prevalence of obesity, defined as body-mass index equal to or
greater than 30 kilograms per mass-squared, was 19.8 percent. The
prevalence of diabetes was 7.3 percent, and the prevalence of
both combined in the same individual was 2.9 percent. The state
of Mississippi had the highest rates of obesity (24.3 percent)
and of diabetes (8.8 percent). Colorado had the lowest rate
obesity (13.8 percent), and Alaska had the lowest rate of
diabetes (4.4 percent). 27 percent of US adults did not engage in
any physical activity, and another 28.2 percent were not
regularly active. Only 24.4 percent of US adults consumed fruits
and vegetables 5 or more times daily. The authors conclude that
the prevalence of obesity and diabetes continues to increase
among US adults, and that interventions are needed to improve
physical activity and diet in communities nationwide.
-----------
J. Am. Med. Assoc. 2001 286:1185
----------
Related Background:
CONCERN OVER WORLD INCREASE IN OBESITY PREVALENCE
Obesity, which is defined as the excessive accumulation of body
fat, has apparently become a problem of international concern.
The World Health Organization and the International Obesity Task
Force have declared "an obesity epidemic on a global scale." The
index used to assess obesity is the so-called Body-Mass Index,
defined as the ratio of weight in kilograms to height in meters
squared: W/M^(2). Clinical obesity is defined as a Body-Mass
Index greater than 30. At the present time, 22.5 percent of the
US population is considered to be clinically obese, compared to
only 14.5 percent in 1980. The increase is apparently seen in all
demographic groups, including children. Comparable increases have
been noted in the United Kingdom, Brazil, Canada, and Australia.
Although experts evidently agree the worldwide increase has been
substantial during the past 15 years, the cause remains a puzzle.
-----------
Science 1998 280:1367
-----------
Related Background:
OBESITY AND MORTALITY: SPINNING SCIENCE NEWS
Stevens et al (6 authors at 4 installations, US), in a study of
the mortality of 62,116 men and 262,019 women during a 12 year
period (1960-1972), report that excess body weight increases the
risk of death from any cause and from cardiovascular disease in
adults between 30 and 74 years of age, and that the relative risk
associated with greater body weight is higher among younger
subjects. The above words are essentially the exact conclusions
chosen to be published by the authors. Nevertheless, two variants
of contrary journalistic "spin" have appeared, an interesting
illustration of how public health news is formulated. In the
first variant, in an editorial in the same journal in which the
Stevens et al report appeared, two journal editors emphasize that
the mortality increase with body-mass is modest and age-
dependent, and they urge an end to people "suffering immeasurable
torment in fruitless weight-loss schemes and scams." In the
second variant, published by the New York Times and echoed by
many newspapers across the US, news items took note of the
journal editorial and went a step further in headlines suggesting
excess weight has now been shown to be harmless. The spin-logic
in the case of both the journal editors and the news media is
apparently that since the effect is small, the public can well
disregard it. The researchers and authors of the article,
however, apparently believe otherwise, and the last sentence of
their article is unequivocal: "In healthy white adults below the
age of 75 who have never smoked cigarettes, our results are
consistent with the healthy weight ranges proposed in the 1995
Dietary Guidelines for Americans."
-----------
New Engl. J. Med. 1998 1 Jan 98
-----------
Related Background:
FIRST IDENTIFICATION OF MOUSE OBESITY GENE IN HUMANS
In 1994 an obesity gene and its protein product (leptin), were
discovered in obese mice. It has been determined that a defect in
the gene causes a severe reduction in the output of functional
leptin by fat cells (adipocytes). Leptin apparently acts as a
messenger to the hypothalamus in the brain, the absence of the
protein causing excessive eating behavior without satiation. Now
a similar gene has been discovered in humans, this gene also
responsible for the production of leptin by human adipocytes.
Carl T. Montague et al (15 authors at various installations, UK)
studied a homozygous genetic defect in two children suffering
from extreme obesity, and have isolated and characterized the
gene, and related it to the previously identified mouse gene
known as ob/ob. As in mice, the result of a defect in the gene is
an order of magnitude reduction in the circulating blood
concentration of the protein leptin. The results do not mean that
all instances of obesity in humans are produced by defects in
this gene, but certainly a new area of research into the
molecular genetics of human obesity has now been defined. In
addition, the authors offer the hope that recombinant human
leptin may be found to correct leptin deficiency in clinical
cases.
-----------
Nature 1997 26 Jun 97
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
15. RETINAL IMPLANTS AND RESTORATION OF VISION
Eberhart Zrenner (University of Tuebingen, DE) discusses retinal
implants, the author making the following points:
1) Vision is an enormously complex form of information
processing that depends on a remarkable neuroprocessor at the
back of the called the "retina". Seeing is initiated when light
passing through the pupil of the eye is focused by the lens onto
the retina's sensory neuroepithelium. This results in the
projection of a reduced upside-down image of the object onto the
approximately 130 million photoreceptor cells (rods and cones) in
the outermost layer of the retina. The cones, providing chromatic
(color) images of high spatial resolution, and the rods, required
for achromatic vision with less spatial resolution in dim light,
transform local luminance and color patterns of the projected
image into electrical and chemical signals. These signals then
activate a complex circuit of retinal neurons: horizontal cells,
bipolar cells, amacrine cells, and ganglion cells. Visual
information from the retina's 130 million photoreceptors is
compressed into electrical signals carried by 1.2 million highly
specialized ganglion neurons, whose axons form the optic nerve.
The optic nerve transmits visual information via the lateral
geniculate nucleus to the primary visual cortex of the brain.
2) Blindness can result when any step of the optical pathway
-- the optics, the retina, the optic nerve, visual cortex, or
other cortical areas involved in the processing of vision --
sustains damage. In Germany, 17,000 patients become blind every
year for whom there is no effective treatment or cure;
approximately 50 percent of all blindness is caused by damage to
the retina. Blinding diseases, such as retinal pigmentosa or age-
related macular degeneration (the most common form of blindness
in the elderly), cause progressive degeneration of the outer
retina. Although there are many examples of electrical devices
that can support or replace the function of defective tissues --
such as cochlear implants for the hearing impaired or pacemakers
for individuals with heart disease -- restoring vision with
electrical devices implanted into the retina is much more
difficult. The transformation of visual scenes into the
electrical "images" carried by the optic nerve to the brain
requires that numerous sensory neurons are stimulated in parallel
and in a spatially correct order to enable 3-dimensional objects
to be accurately encoded.
3) In summary: At the present time, a number of research
groups are developing electrical implants that can be attached
directly to the retina in an attempt to restore vision to
patients suffering from retinal degeneration. However, despite
promising results in animal experiments, there are still several
major obstacles to overcome before retinal prostheses can be used
clinically.
-----------
Science 2002 295:1022
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
16. ON POSTPARTUM DEPRESSION
Laura J. Miller (University of Illinois Chicago, US) discusses
postpartum depression, the author making the following points:
1) The devastating familial consequences of postpartum
depression have been underscored by recent media attention to
women who have killed themselves or their children while
depressed. There are two leading hypotheses providing an
explanation of "postpartum blues". The first is that the mood
changes stem from abrupt hormone withdrawal. Supporting evidence
includes the finding that absolute levels of estrogens and
progesterone are unrelated to postpartum blues, but the greater
the change between pregnancy and postpartum levels, the greater
the likelihood of developing postpartum blues. In addition, the
progesterone metabolite allopregnanolone, an anxiolytic gamma-
aminobutyric acid agonist, is significantly lower in women with
postpartum blues.
2) A second hypothesis is that postpartum blues stem from
activation of an evolved biological system underlying mammalian
mother-infant attachment behavior, regulated primarily by the
hormone oxytocin. There is direct evidence for this effect in
nonprimate mammals: rodent mothers whose oxytocin-producing cells
have been removed exhibit significantly less maternal behavior
than rodents undergoing sham surgery. Indirect evidence suggests
similar but more versatile mechanisms in humans and other
primates. Under conditions of ample support and low stress, these
neurophysiologic changes promote attachment between mothers and
infants. However, under conditions of high stress and inadequate
support, this emotional reactivity may increase vulnerability to
depression by rendering a woman more susceptible to stress.
-----------
J. Am. Med. Assoc. 2002 287:762
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
17. ON FITNESS AND SURVIVAL
Gary J. Balady (Boston Medical Center, US) discusses physical
fitness, the author making the following points:
1) In 1859, Charles Darwin published his theory of evolution
as an incessant struggle among individuals with different degrees
of fitness within a species. Although at that time, his
explanations created remarkable controversy, they were to
revolutionize the course of science. Darwin's writings reflected
conclusions drawn from years of study and observation. Now,
nearly 150 years later, in the era of evidence-based medicine and
rigorous scientific method, when fitness is quantitatively
measured and study subjects are followed for years, the data
supporting the concept of survival of the fittest are strong and
compelling. During the past 15 years, many long-term
epidemiologic studies have shown an unequivocal and robust
relation of fitness, physical activity, and exercise to reduced
mortality overall, to reduced mortality from cardiovascular
causes, and to reduced cardiovascular risk.
2) Cardiorespiratory fitness, or physical fitness, is a set
of attributes that enables a person to perform physical activity.
It is determined, in part, by habitual physical activity and is
also influenced by several other factors, including age, sex,
heredity, and medical status. Physical fitness is best assessed
by a measure of maximal or peak oxygen uptake (volume of oxygen
consumed, measured in milliliters of oxygen per kilogram of body
weight per minute), which is viewed as an index of energy
expenditure.
3) It is now becoming clear that exercise modulates many
biologic mechanisms to confer cardioprotection. Exercise improves
the lipid profile and glucose tolerance, reduces obesity, and
lowers blood pressure. However, modification of atherosclerotic
risk factors does not fully explain the benefits that have been
observed. Positive effects of exercise on vascular function,
autonomic tone, blood coagulation, and inflammation are likely to
contribute to improved cardiovascular health and survival.
-----------
New Engl. J. Med. 2002 346:852
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
18. ON COCHLEAR IMPLANTS AND OTHER HEARING DEVICES
J.P. Rauschecker and R.V. Shannon (Georgetown University, US)
discuss cochlear implants and other auditory devices, the authors
making the following points:
1) Partial or total hearing loss has many different causes.
Defects in either the outer ear or middle ear (composed of the
tympanic membrane, ear drum, and auditory ossicles) result in a
conductive hearing loss that can usually be remedied by insertion
of a hearing aid, which amplifies sound vibrations. Profound
deafness, on the other hand, is caused by loss of the sensory
hair cells in the fluid-filled snail-shaped inner ear (cochlea),
the cells that transduce sound waves into electrical impulses,
which are then transmitted to the brain.
2) Profoundly deaf individuals who still have an intact
auditory nerve have profited from the dramatic advances made over
the past 30 years in the field of cochlear implants. The cochlear
implant is a microelectrode array implanted in the cochlea that
directly stimulates the auditory nerve. With more than 40,000
patients worldwide, the success of these devices is nothing short
of miraculous. Most adults with cochlear implants are able to
converse on the phone, and most children with such implants are
able to be educated in mainstream classrooms.
3) For some profoundly deaf individuals, however, electrical
stimulation of the inner ear with a cochlear implant is not a
feasible prosthesis owing to an absence or destruction of the
auditory nerve. Instead, an auditory prosthesis consisting of a
microelectrode array that directly stimulates one of the auditory
processing centers of the brainstem, bypassing the cochlea and
auditory nerve, might restore hearing to these patients. Such
auditory brainstem implants have been under development since the
late 1970s, pioneered by physicians and researchers at the House
Ear Institute in Los Angeles, but so far have had only limited
success.
-----------
Science 2002 295:1027
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
19. ON CHEMISORBATE BONDING
M.F. Mrozek et al (Purdue University, US) discuss chemisorbate
bonding, the authors making the following points:
1) Understanding how chemisorbate binding depends on the
chemical nature of the metal surface is an issue of major
fundamental significance in electrochemistry as well as in
ultrahigh vacuum-based surface science. For the latter type of
interface, experimental information regarding metal-chemisorbate
interactions is attainable in several ways, including
temperature-dependent desorption along with electronic and
vibrational spectroscopies. For in situ chemical interfaces,
however, the breadth of available molecular-level probes is
considerably narrower. Although infrared reflection-absorption
spectroscopy has found extensive application at electrochemical
as well as metal ultrahigh vacuum interfaces, the limitations set
by sensitivity, selection rules, and solution=phase interferences
place restrictions on the type of vibrational modes (and hence
the range of adsorbate molecules) suitable for characterization
by electrochemical infrared reflection-absorption spectroscopy.
The other type of vibrational technique commonly applied to
electrochemical interfaces, surface-enhanced Raman spectroscopy,
offers typically higher sensitivity, more liberal selection
rules, and a wider effective wavenumber range.
2) The authors report detailed intramolecular vibrational
spectra obtained by means of surface-enhanced Raman scattering
for benzonitrile adsorbed on 7 different electrode surfaces,
including platinum, palladium, rhodium, iridium, copper, silver,
and gold. The experimental spectra are compared with ab initio
calculations of vibrational frequencies, bond geometries, and
charge distributions obtained by density functional theory. The
authors suggest their results provide a benchmark illustration of
the virtues of density functional theory in interpreting complex
vibrational spectra for larger polyatomic adsorbates.
-----------
J. Am. Chem. Soc. 2001 123:12817
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
20. GAS HYDRATES AND GEOCHEMICAL CARBON DIOXIDE STORAGE
Y. Halpern et al (Argonne National Laboratory, US) discuss gas
hydrates, the authors making the following points:
1) Clathrate hydrates are a general class of compounds
composed of water and gas molecules. They usually form at high
pressures and low temperatures, although a few clathrates are
stable at ambient pressure. The natural occurrence of gas
hydrates, as well as environmental concerns over the increase of
carbon dioxide in the atmosphere, has led to speculation that
carbon dioxide could be stored in hydrate form on the ocean
floor. This could be achieved by sequestering the excess carbon
dioxide within a hydrate framework. Moreover, it may be possible
to simultaneously extract the methane from methane hydrate
reserves on the ocean floor and replace the guest molecule with
carbon dioxide.
2) At temperatures and pressures found at a kilometer or
more in depth in the ocean, carbon dioxide is a liquid. In
experiments in which carbon dioxide is transported to the ocean
floor, it is shown to pool as a liquid and react with the
seawater to produce carbon dioxide hydrate. However, it could
also interact with other existing hydrates. Because of this, the
environmental and safety issues, and possible potential benefits,
of direct exposure of hydrates on the ocean floor to liquid
carbon dioxide need to be examined.
-----------
J. Am. Chem. Soc. 2001 123:12826
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
21. SOIL FERTILITY AND HUNGER IN AFRICA
Pedro A. Sanchez (University of California Berkeley, US)
discusses hunger in Africa, the author making the following
points:
1) Africa south of the Sahara is the only remaining region
of the world where per capita food production has remained
stagnant over the past 40 years. Approximately 180 million
Africans (up 100 percent since 1970) do not have access to
sufficient food to lead healthy and productive lives, making them
more susceptible to the ravages of malaria, HIV-AIDS, and
tuberculosis. Absolute poverty -- characterized by incomes of
less than US$1 per person per day -- is coupled with an
increasingly damaged natural resource base.
2) Efforts focused on child survival, coping with HIV-AIDS,
improving governance, increasing foreign investment, breaking
trade barriers, and providing debt relief are all necessary, but
they are insufficient because they do not directly address
agriculture, the economic sector that engages 70 percent of all
Africans. Africa's food insecurity is directly related to
insufficient total food production, in contrast to south Asia and
other regions, where food insecurity is primarily due to poor
distribution and lack of purchasing power. African agriculture
has performed dismally, in sharp contrast to Asia and Latin
America, regions that benefitted from the Green Revolution, and
some African states and developed countries are now considering
restoring high priority to agricultural development in Africa.
3) Depletion of soil fertility, along with the concomitant
problems of weeds, pests, and diseases is a major biophysical
cause of low per capita food production in Africa. This is the
result of the breakdown of traditional practices and the low
priority given by governments to the rural sector. Over decades,
small-scale farmers have removed large quantities of nutrients
from their soils without using sufficient quantities of manure or
fertilizer to replenish the soil. This has resulted in a very
high annual depletion rate of nitrogen, phosphorus, and potassium
in cultivated land in 37 African countries over the last 30
years. The potential of genetically improved crops cannot be
realized when soils are depleted of plant nutrients.
-----------
Science 2002 295:2019
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
22. ON HEALTH OF THE GLOBAL POOR
P. Jha et al (World Health Organization, US) discuss global
health, the authors making the following points:
1) Improvements in global health in the 2nd half of the 20th
century have been enormous but remain incomplete. Between 1960
and 1995, life-expectancy in low-income countries improved by 22
years as opposed to 9 years in high-income countries. Mortality
of children under 5 years of age in low-income countries has been
halved since 1960. Even so, 10 million child deaths occur
annually, and other enormous health burdens remain.
2) In 1998, almost a third of deaths in low- and middle-
income countries were due to communicable diseases, maternal and
perinatal conditions, and nutritional deficiencies: a death toll
of 16 million, equivalent to the population of Florida. Of those
deaths, 1.6 million were from measles, tetanus, and diphtheria,
diseases routinely vaccinated against in wealthy countries.
3) Of the half million women who die annually due to
pregnancy or childbirth, 99 percent do so in low- and middle-
income countries. Approximately 2.4 billion people live at risk
of malaria, and at least 1 million died from malaria in 1998.
There are 8 million new cases of tuberculosis every year, and 1.5
million deaths from tuberculosis.
4) On the basis of current smoking trends, tobacco-
attributable disease will kill approximately 500 million people
over the next 5 decades. Over 20 million people have died already
of HIV?AIDS, 40 million people are infected currently, and its
spread continues unabated in many countries. The burden falls
most heavily on poor countries and on the poorest of the people
within those countries.
5) Of the 30 million children not receiving basic
immunizations, 27 million live in countries with GNP below $1200
per capita. In India, the prevalence of childhood mortality,
smoking, and tuberculosis is three times higher among the lowest
income or educated groups than among the highest.
-----------
Science 2002 295:2036
----------
Related Background:
PUBLIC HEALTH: EXPECTED CONSEQUENCES OF GLOBAL WARMING
Climate change produced by global warming is expected to result
in melting ice caps, rising sea levels, torrential floods,
devastating droughts, and severe harvest failures. What are often
not considered in discussions of global warming are the effects
of global warming on public health.
... ... Pim Martens (University of Maastricht, NL) presents a
review of the expected effects of global warming on public
health, the author making the following points:
1) Concerning heat stress: The author suggests that perhaps
the most immediate consequence of increasing global temperatures
will be a rise in the number of heat waves and heat-related
illnesses. Such temperature extremes can, for example, increase
the sensitivity of asthmatics to their condition. There will also
be an increasing number of deaths from heat stress brought about
by high ambient temperatures lasting days on end. On the other
hand, the milder winters associated with global warming will
offer a better chance of survival for at-risk groups such as the
elderly during the coldest months. Research into the effect of a
gradual temperature increase has revealed that we can expect a
decline in mortality from cardiovascular and pulmonary disease in
the winter. Whether the milder winters could offset the mortality
during the summer heat waves is not clear.
2) Concerning malaria: The spread of this disease is limited
by conditions that favor the disease vector (the malarial
mosquito Anopheles) and the protozoan parasite (Plasmodium). The
malarial mosquito is most comfortable at temperatures of
approximately 20 to 30 degrees centigrade and at a relative
humidity of at least 60 percent. Also, the malaria parasite
develops more rapidly inside the mosquito as the temperature
rises, and the development ceases entirely below approximately 15
degrees centigrade. Increased rainfall and increased surface
water, expected to result from global warming, will produce more
breeding grounds for the mosquito. Malaria currently kills 1 to 2
million people each year.
3) Concerning schistosomiasis (bilharzia): The enormous
expanse of irrigation systems in many tropical countries has
doubled the incidence of this disease in the past 50 years. There
are some estimates that nearly 200 million people are infected
worldwide. The disease is caused by a parasitic worm (a
trematode; also called a "fluke"; a type of flatworm) whose eggs
enter the water supply by way of human urine or feces. Infected
water snails serve as hosts for the parasites while they develop
into free-swimming "mini-worms" (larvae; cercaria). The circle
closes when a larva penetrates the skin of a human who comes in
contact with the contaminated water. The development of the
parasite and the population of the host snails are both governed
by the ambient temperature, with warm waters favoring their
growth. Also, the warmer the ambient temperature, the more often
people come into contact with water. In places where the disease
is endemic, it is known that the number of infected snails
declines sharply during the winter months. A temperature rise of
only a few degrees will ensure that this disease is transmitted
throughout the year. It is estimated that currently worldwide
approximately 500 million people are at risk of infection by this
pathogen.
4) Concerning dengue: Like malaria, this disease is
transmitted by mosquitoes (Aedes aegypti, which also transmits
yellow fever), but the pathogen is a virus (dengue virus, a
flavivirus). The dengue virus is currently restricted to the
tropics, approximately between latitudes 30 degrees south and 20
degrees north. Temperature affects the development of both the
mosquito and the virus as well as the frequency of mosquito
bites. A warmer climate may increase not only the elevations
above sea level at which the disease occurs, but also its
northern and southern ranges. Dengue hemorrhagic fever, a severe
form of the disease, has a mortality of 6 to 30 percent, with
most deaths occurring in infants less than 1 year old.
5) Concerning various water-borne diseases: Changes in the
amount of precipitation will accompany the temperature changes to
a warmer Earth. Many disease-causing organisms require water for
survival, and increases in rainfall and flooding will encourage
the wider distribution of such pathogens, with higher
temperatures increasing the chances of pathogen survival. Various
bacteria (e.g., Salmonella and Shigella), viruses (e.g.,
rotavirus), protozoa (e.g., Giardia and Cryptosporidium) can
cause diarrhea, which kills more than 3 million children every
year.
6) In general, many factors will interact with a changing
climate in a nonlinear way, so their effects on human health are
extremely difficult to quantify. Despite the uncertainties, there
are increasing indications that a changed global climate may be a
major factor in the global distribution of many diseases.
-----------
American Scientist 1999 87:534
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
23. IMAGING THE STRUCTURES OF NANOMATERIALS
P.L. Hansen et al (University of Copenhagen, DK) discuss imaging
nanomaterials, the authors making the following points:
1) The size, shape, and structure of a nanomaterial affect
its catalytic, optical, and electronic properties in ways that
are difficult to predict. Procedures for synthesis of
nanoparticles with well-defined shapes offer possibilities for
addressing these issues. The stability of the synthesized shapes
is not, however, guaranteed. In situ studies of metallic
nanoparticles for applications in catalysis have demonstrated
that the state of the material may change from the as-synthesized
state and may depend on the conditions encountered during
catalysis. In situ spectroscopic methods now allow direct
investigations of the nanoparticles under relevant catalytic
conditions, but complementary atomic-level, real-space
information on the dynamic structure and morphology changes of
metallic particles under similar conditions has not been
available.
2) Transmission electron microscopy provides real-space
images with a resolution down to 0.1 nanometers. However, this
technique has been used mainly for ex situ studies of the atomic
structure of supported nanoparticles after various treatments.
The authors report the use of in situ transmission electron
microscopy to obtain atom-resolved images of copper nanocrystals
on different supports. These crystals are catalysts for methanol
synthesis and hydrocarbon conversion processes for fuel cells,
the nanocrystals undergo dynamic reversible shape changes in
response to changes in the gaseous environment. For zinc-oxide
supported samples, the changes are caused both by adsorbate-
induced changes in surface energies and by changes in the
interfacial energy. For copper nanocrystals supported on silica,
the support has negligible influence on the structure. The
authors suggest that nanoparticle dynamics must be included in
the description of catalytic and other properties of
nanomaterials, and that in situ microscopy offers possibilities
for obtaining the relevant atomic-scale insight.
-----------
Science 2002 295:2053
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
24. ON ULTRATHIN POLYMER FILMS AT INTERFACES
S. Nagano and T. Seki (Tokyo Institute of Technology, JP) discuss
ultrathin polymer films, the authors making the following points:
1) The conformational and morphological behavior of
ultrathin polymer films at interfaces is of fundamental
importance to a large number of technological applications such
as electric packaging, dielectric layers, coatings, composites,
and lubrication, and considerable theoretical and experimental
progress has recently been made in describing polymers in contact
with surfaces and interfaces.
2) When the thickness of a polymer film reaches to a level
of a few radii of molecular gyration, thermophysical properties
(e.g., glass transition temperature) and structures (e.g.,
molecular orientation, aggregation state, and crystallinity) are
modified from those in a bulk state by the 2-dimensional
geometrical constraint. Such ultrathin films of polymers are
mostly prepared by the solvent-spincast method. This method is
widely applicable for many sorts of soluble polymers, but it does
not allow precise thickness controls at nanometer levels. In
contrast, the Langmuir-Blodgett method utilizing monolayer
formation on water allows precise nanometer thickness controls
via layer-by-layer deposition ("bottom up" approach). However
this method has the inconvenient restriction that the polymers
need to possess polar moieties (need to be amphiphiles). Fully
hydrophobic soluble polymers such as polystyrene and polysilanes
(Si-catenated polymers) having hydrocarbon constituents cannot be
used in a monolayer technique. Some attempts at Langmuir-Blodgett
deposition have been made for such polymers by mixing with
monolayer-forming long-chain carboxylic acid, but the polymers
are segregated within the Langmuir-Blodgett films and the
monolayer spreading of such polymers has not been accomplished.
3) The authors report they have successfully and for the
first time achieved build-up Langmuir-Blodgett manipulation of
fully hydrophobic polymers via the use of a cospreading species
to assist spreading on water.
-----------
J. Am. Chem. Soc. 2002 124:2074
----------
Related Background:
DENDRIMERS IN LANGMUIR FILMS
J-F. Nierengarten et al (Louis Pasteur University Strasbourg, FR)
discuss amphiphilic dendrimers. Growing attention is currently
devoted to large dendritic structures for applications in
nanotechnology and materials science. Of interest is the
incorporation of such components into thin ordered films, and one
of the most widely pursued approaches toward structurally ordered
dendrimer assemblies has been the preparation of Langmuir films
at the air-water interface. For example, successful preparation
of Langmuir monolayers has been achieved with poly(propylene
imine) dendrimers substituted with peripheral long alkyl chains.
In this case, thanks to the high flexibility of the dendrimer,
the compounds are able to adopt a cylindrical amphoteric shape,
in which the dendritic poly(propylene imine) part acts as a polar
head group and alkyl chains packed together form a hydrophobic
moiety. It has also been shown that dendrimers with peripheral
polar headgroups can be used for the preparation of thin ordered
films at the air-water interface. However, such a strategy
appears limited, since at high densities the dendrimer is water
soluble due to the presence of too many polar units. Langmuir
films have also been obtained with amphiphilic dendritic
molecules with a small polar headgroup at the focal point.
However, the stability of the films appears to be a problem
because of the difference in size between the hydrophobic and
hydrophilic groups. The authors report that the peripheral
substitution of a globular dendrimer with hydrophobic chains on
one hemisphere and hydrophilic groups on the other hemisphere
provides the perfect hydrophobic/hydrophilic balance allowing the
formation of stable Langmuir films.
-----------
J. Am. Chem. Soc. 2001 123:9743
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
25. IN FOCUS: ON HUMAN SPEECH
"The human ability to speak is universal. All normal children
acquire the language of their environment at a very early age.
Most start babbling at the age of 7 months, produce a few
meaningful words around their first birthday, reach a 50-word
vocabulary 6 months later, produce their first multi-word
utterances by the end of their second year of life, and begin
expressing syntactic relations by means of prepositions,
auxiliaries, inflections, and word order in the course of their
third year. By the age of 5 or 6, the basic architecture of this
natural skill is essentially in place. Although our ability to
speak has for millennia been recognized as uniquely human, as
species-specific, as the basis of our cultural evolution, and
generally as a core aspect of the human condition (homo loquens),
the systematic study of how we speak did not begin before the end
of the 19th century. In 1900, Wilhelm Wundt [1832-1920] published
his theory about how a sentence emerges in the speaker's mind, a
theory entirely based on introspection. With their 1896
monograph, Meringer and Mayer initiated an important empirical
paradigm. They collected and analyzed a large corpus of
spontaneously produced speech errors that they had carefully
noted down. One of their findings was that word substitutions
were either meaning-based [e.g., (Ihre) your for (meine) mine] or
form-based [e.g., Studien (studies) for Stunden (hours)],
suggesting a distinction between meaning- and form-based
operations in word generation. It was only by the 1970s that this
paradigm became fully exploited to construct theories of
utterance generation."
-----------
Willem J.M. Levelt: "Spoken Word Production: A Theory of Lexical
Access."
Proc. Nat. Acad. Sci. 2001 98:13464
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
26. FROM THE SW ARCHIVE:
SCIENCE IN THE NEXT 50 YEARS: WHICH QUESTIONS? WHAT ANSWERS?
At this moment of calendar turning, there is an urge to look
forward and envision the future. In science, however, looking
forward often means peering into a fog and making guesses about
shapes and wisps and paths that suddenly change. Directions in
research are dependent on questions, and new and important
questions often require the new perspectives of a new generation.
But something seems afoot: there is a growing feeling in the
scientific community that we are proceeding at high speed into
three momentous scientific revolutions -- one in fundamental
physics, one in molecular genetics, and one in the biology of
cognition. There is a story (which may be false) that 100 years
ago a number of prominent researchers felt a contentment that the
outlines of the major sciences were already completely drawn.
Now, at the start of this new century and new millennium, few if
any people believe that about current science, and in general
there is the view that we are really only at the beginning of
things. John Maddox, a one-time theoretical physicist who spent a
total of 22 years as editor-in-chief of the journal _Nature_
(succeeded by Philip Campbell in 1995), presents an essay on the
near future of science -- the next 50 years, and he takes note of
the deeper understanding of fundamental physics, molecular
genetics, and the biology of cognition that will likely occur
during this coming century. The author makes the following
points:
1) Concerning fundamental physics: The central problem in
fundamental physics derives from the fact that quantum mechanics
and Einstein's theory of gravitation (the General Theory of
Relativity) are incompatible with each other. Without a bridge of
some kind between these two theories, it will not be possible to
describe in detail the *Big Bang origin of the Universe. Doubt
has also invaded particle physics, where for many years
researchers have shared the goal that all *4 forces of nature
should eventually be unified. Researchers in *string theory
believe their work provides an acceptable bridge, "but others
point to the waxing and waning of enthusiasm in the past 20 years
and are less sanguine. At least the next 50 years should show
which camp is correct."
2) Concerning molecular genetics: The author suggests the 50
years ahead will see an intensification of current efforts to
identify the genetic correlates of evolution. Comparison of the
amino acid sequences of similar proteins from related species, or
of the sequences of nucleotides in related nucleic acids, is in
principle a means of determining the age of the common ancestor
of the two species -- provided the rate at which mutations
naturally occur in these molecules is known. That is not a simple
issue, but it is a goal for the near future. With luck, the same
effort will also reveal the role of virus-like agents in the
early evolution of life. The human genome, for example, is
crammed with DNA sequences that appear to be nucleic acid fossils
of a time when genetic information was readily transferred
between different species. The author suggests "we shall not know
our true place in nature until we understand how the apparently
useless DNA in the human genome (which Crick was the first to
call 'junk') contributed to our evolution." The author also
suggests that in the context of molecular genetics, "one prize
now almost ready for the taking is the reconstruction of the
genetic history of the human race, Homo sapiens." It is only a
matter of time before the genes involved in the successive stages
of human individual development are listed in the order in which
they come into play. "Then it will be possible to tell from a
comparison between human and, say, chimpanzee genes when and in
what manner the crucial differences between humans and the great
apes came into being."
3) Concerning the biology of cognition: Our understanding of
the human brain is incomplete in one conspicuous way: nobody
understands how decisions are made or how imagination is set
free. What consciousness consists of (or how it should be
defined) is equally a puzzle. The essence of the difficulty is to
identify what patterns of neuron activity in the head signal
making a decision or signal other cognitive activity. Decision-
making may have several neural correlates, which will complicate
the search, but "there is no reason to believe the problem is
intractable."
4) The author concludes: "And we shall be surprised. The
discovery of living things of some kind elsewhere in the Galaxy
would radically change the general opinion of our place in
nature, but there will be more subtle surprises, which, of
necessity, cannot be anticipated. They are the means by which the
record of the past 500 years of science has been repeatedly
enlivened. They are also the means by which the half-century
ahead will enthrall the practitioners and change the lives of the
rest of us."
-----------
Scientific American 1999 December
-----------
Text Notes:
... ... *Big Bang origin of the Universe: The Big Bang theory is
the general cosmological model that proposes that all matter and
radiation in the universe originated in an explosion at a finite
time in the past.
... ... *4 forces of nature: The 4 fundamental forces comprise
the gravitational force, the electromagnetic force, the nuclear
strong force, and the nuclear weak force.
... ... *string theory: In particle physics, string theory is a
theory of elementary particles based on the idea that the
fundamental entities are not point-like particles but finite
lines (strings), or closed loops formed by strings, the strings
one-dimensional curves with zero thickness and lengths (or loop
diameters) of the order of the Planck length of 10^(-35) meters.
-----------
ScienceWeek 5 Apr 2002 www.scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
In the text, the affiliation following the names of authors in
sources with more than one author is the affiliation of the lead
author.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
NOTICES
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
CHANGE OF EMAIL ADDRESS:
If at any time you need to change the Email address at which you
receive SW, please send the information to:
request@scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
SCIENCE-WEEK SUBSCRIPTIONS:
Professional Personal Subscriptions: 1 year $50, 2 years $80
Student Subscriptions: 1 year $25
Institutional Subscriptions: 1 year $200, 2 years $350
Further information concerning subscriptions is available at:
http://www.scienceweek.com/subinfo.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
We welcome comments, suggestions, and criticisms from our
subscribers. Public letters relevant to any report are also
welcome. Editorial contact: editors@scienceweek.com
Editor/Publisher: Dan Agin
Managing Editor: Claire Haller
Associate Editor: Joan Oliner
Copyright (c) 1997-2002 SCIENCE-WEEK
All Rights Reserved
US Library of Congress ISSN 1529-1472
---------------------------------------------
ScienceWeek/Spectrum Press Inc.
3023 N. Clark Street #109
Chicago, 60657-5205 IL, USA.
---------------------------------------------
-----end file
|