ScienceWeek BULLETIN August 18, 1999

Larry Klaes (
Thu, 19 Aug 1999 13:21:15 -0400

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>Date: Wed, 18 Aug 1999 08:59:25 -0600
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>SW BULLETIN - August 18, 1999
>Today's News in the Sciences:

>Planetary Science/Chemistry
>Evolutionary Biology
>Molecular Biology
>Medical Biology/Epidemiology
>ASTROCHEMISTRY: One of the great puzzles of biology is the
>homochirality of most amino acids and sugars present in
>biological systems. In general, chirality is a property of
>certain asymmetric objects such that the object and its mirror
>image cannot be superimposed one on the other while both objects
>are restricted to the same plane (e.g., a left- and right-handed
>glove). Stuart Clark (UK) presents a review of recent
>astronomical observations that suggest a solution to the puzzle.
>The idea is that planets forming around stars in regions bathed
>in ultraviolet light with high circular polarization will
>naturally incorporate amino acids with enantiomeric excesses of
>one sort or the other, and that the same probably held true for
>Earth approximately 5 billion years ago. The author suggests that
>one consequence of this hypothesis is that if carbon-based life
>exists on extrasolar planets, a biochemistry based on D- amino
>acids could well be the rule.
>Since the reports in recent years that the Martian meteorite
>ALH84001 contained possible evidence for life on Mars,
>essentially all of the ensuing controversy has focused on Martian
>meteorites collected in Antarctica, and little attention has been
>directed to other classes of meteorites, many of which did not
>fall in Antarctica. Now D.P. Glavin et al (US) report they have
>detected, with high-performance liquid chromatography, a suite of
>protein and nonprotein amino acids in the water- and acid-soluble
>components of an interior fragment of the Martian meteorite
>Nakhla, which fell in Egypt in 1911. Aspartic and glutamic acids,
>glycine, alanine, beta-alanine, gamma-amino-butyric acid were the
>most abundant amino acids detected. The authors report that the
>amino acid distribution in the Nakhla meteorite, including the
>D/L ratios, is similar to what is found in bacterially degraded
>organic matter. The authors suggest the amino acids in the Nakhla
>meteorite appear to be derived from terrestrial organic matter
>that infiltrated the meteorite soon after its fall to Earth,
>although it is possible that some of the amino acids are
>endogenous to the meteorite. The authors suggest that rapid amino
>acid contamination of Martian meteorites after direct exposure to
>the terrestrial environment has important implications for Mars
>sample-return missions and the curation of the samples from the
>time of their delivery to Earth. (PNAS-2)
>PHYSICS: In the physics of superconductors, "Cooper pairs" are
>pairs of bound electrons, the pairs occurring in a
>superconducting medium according to the Bardeen-Cooper-Schrieffer
>theory of superconductivity. A variety of materials exhibit
>superconductivity, and the mechanisms underlying the phenomenon
>are less clear in some cases than in others. Despite 12 years of
>intensive experimental and theoretical research on high-
>temperature cuprate superconductors, the question of the
>mechanism of superconductivity in these materials still lacks an
>answer that commands even majority, let alone universal, support.
>Now. A.J. Leggett (US) suggests that the mechanism of
>superconductivity in the cuprates is a saving, due to the
>improved screening resulting from Cooper pair formation, of the
>part of the Coulomb energy associated with long wavelengths and
>mid-infrared frequencies. The author suggests this scenario
>(called MIR, for "mid-infrared") provides a plausible explanation
>of the trend of transition temperature with layering in the Ca-
>spaced cuprates, and that existing experimental results appear to
>be consistent with this scenario. (PNAS)
>ECOLOGY/OCEANOGRAPHY: In ecology and oceanography, the term
>"primary production" refers to the creation of organic matter
>(biomass) through photosynthesis or chemosynthesis. There are two
>views of how primary production in most of the world's oceans is
>controlled: the "geochemists' view" (phosphorus regulation) and
>the "biologists' view" (nitrogen regulation). Toby Tyrrell (UK)
>presents a model that the author suggests has the potential to
>resolve the long-running debate among oceanographers over whether
>nitrogen or phosphorus exerts overall control on oceanic primary
>production. In the work of the author, a representation of the
>competition between nitrogen-fixing and other phytoplankton is
>inserted into a two-box global model of the oceanic nitrogen and
>phosphorus cycles. Homeostatic regulation of both nitrate and
>phosphate concentrations results, with surface waters more
>deficient in nitrate than phosphate in steady state, but with
>external phosphate inputs controlling longer-term primary
>production in the global ocean. (NAT)
>EVOLUTIONARY BIOLOGY: Microfossils, stromatolites, and
>sedimentary carbon isotope ratios all indicate that microbial
>organisms inhabited the oceans in Archean times (i.e., more than
>2.5 million years ago). But these lines of evidence are not very
>informative about what these microbes were or how they lived.
>J.J. Brocks et al (AU) now report molecular fossils in late
>Archean shales (2.7 million years old) in Australia that have
>suffered only minimal metamorphism. These molecular fossils
>reveal that the Archean biota was considerably more complex than
>currently recognized, and that the domains Eucarya and Bacteria
>were already extant. The authors suggest that the presence of
>steranes, particularly cholestane and its 28- to 30-carbon
>analogs, provides persuasive evidence for the existence of
>eukaryotes 500 million years to 1 billion years before the
>extant fossil record indicates that the lineage arose. (SCI)
>MOLECULAR BIOLOGY: Biological cells in tissues reside in a
>protein network, the extracellular matrix, which the cells
>secrete and mold into the intercellular space, and the
>extracellular matrix in turn exerts profound control over cells.
>F.G. Giancotti and E. Ruoslahti (US) present a review of the
>interaction. The effects of the matrix are primarily mediated by
>integrins, a family of cell surface receptors that attach cells
>to the matrix and mediate mechanical and chemical signals from
>it. These signals regulate the activities of cytoplasmic kinases,
>growth factor receptors, and ion channels, and control the
>organization of the intracellular actin cytoskeleton. Many
>integrin signals converge on cell regulation, directing the cells
>to live or die, to proliferate, or to exit the cell cycle and
>differentiate. (SCI)
>MEDICAL BIOLOGY/EPIDEMIOLOGY: Hepatitis C virus (HCV) infection
>is a leading cause of chronic liver disease in the US, but the
>true prevalence of HCV infection in the US is uncertain. Now M.J.
>Alter et al (US) report a study testing serum samples from 21,241
>persons 6 years or older, and determination of the prevalence of
>HCV RNA by means of nucleic acid amplification, and determination
>of genotype by means of sequencing. The authors report the
>results indicate an estimated 3.9 million persons nationwide with
>HCV, and 2.7 million persons chronically infected with the virus.
>The authors suggest that people who use illegal drugs or engage
>in high-risk sexual behavior account for most of the persons with
>HCV infection. Most HCV infected persons are younger than 50
>years of age, so that the burden of disease associated with HCV
>is likely to increase during the next 10 to 20 years as this
>cohort reaches the age at which complications of chronic liver
>disease typically occur. The authors suggest that the frequency
>of such complications might be reduced if infected persons were
>identified and provided with counseling and appropriate medical
>care. (NEJM)
>AS: Amer. Scientist Jul/Aug 99
>NAT: Nature 5 Aug 99
>NEJM: New England J. Med. 19 Aug 99
>PNAS: Proc. Natl. Acad. Sci. US 20 Jul 99
>PNAS-2: Proc. Natl. Acad. Sci. US 3 Aug 99
>SCI: Science 13 Aug 99
>SW: ScienceWeek 20 Aug 99
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