[escepticos] Science-Week Oct 24, 1997 -LEEDLO-

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>SCIENCE-WEEK
>
>A Free Weekly Digest of the News of Science
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>October 24, 1997
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>---------------------------------------------
>
>Reported in This Issue
>
>1. Irish Activist Group Sabotages Genetically Engineered Crop
>2. National Cancer Institute Releases Nuclear Fallout Report
>3. A Workshop on Chondrite Meteorites
>4. Fractional Electrons in Condensed Matter Physics
>5. Long Range Order in Stacks of Fluid Monolayers
>6. A New Approach to the De Novo Design of Proteins
>7. Specification of Cell Affinities by an Intercellular Signal
>8. New Data Against Important Telomerase Role in Cancer
>9. Role of Kainate Receptors in Synaptic Transmission
>10. Increasing U.S. Prevalence of Herpes Simplex Viral Disease
>
>
>This week's SCIENCE-REPORT contains the following reports
>in addition to those listed above (see Notices Section):
>
>Cassini Mission to Saturn Imminent Despite Risk Concerns
>An Historic Meeting Devoted to Gamma Ray Bursts
>A Review of the History of the Electron
>A Review of the History of Leptons
>Origin of Rubber-Like Behavior of Certain Metal Alloys
>Structural Adaptations of Cell Molecular Motors
>Relationship Between Outward K+ Current and Neuron Apoptosis
>Molecular and Cellular Basis of Drug Addiction
>Toxic Liver Effects of Excessive Tylenol (Acetaminophen) Use
>Attenuated AIDS Vaccine May Be Too Dangerous for Use
>
>---------------------------------------------
>
>1. IRISH ACTIVIST GROUP SABOTAGES GENETICALLY ENGINEERED CROP
>In Ireland, an environmental activist group called the Gaelic
>Earth Liberation Front has destroyed a one-acre research crop of
>genetically engineered sugar beet. Under the auspices of the
>Irish Government, the crop was grown by the US chemical company
>Monsanto to develop a sugar beet variety resistant to a widely
>used herbicide. The Gaelic Earth Liberation Front said in a
>statement: "This was Ireland's first genetically engineered crop
>and we hope it will be the last." But of course it will not be
>the last, and one wonders if this is activism for the sake of
>activism by people who known little about the environment and
>even less about biology. Patricia McKenna, a politician who
>represents Dublin in the European Parliament, praised the
>destruction of the sugar beet crop, accusing Monsanto and the
>Irish government of "playing games with the Irish environment".
>And that underscores the non-triviality of these events. The neo-
>Luddite rumblings that are becoming common these days are useful
>to some people with political power, which means both the source
>of the rumblings and the politicians who use the rumblings need
>to be confronted by the scientific community. Ultimately it is
>the larger community which must be persuaded one way or the
>other; it is the attitude of the larger community that will
>determine the fate of the neo-Luddite groups and the politicians
>who use them. Concerning the science involved, what is obvious to
>the scientific community is not always obvious to the community
>at large, and one can only hope the scientific community will see
>its responsibility to make its case to the larger community by
>forceful and articulate dissemination of information. There is no
>other apparent reasonable road. (Nature 9 Oct 1997)
>
>2. NATIONAL CANCER INSTITUTE RELEASES NUCLEAR FALLOUT REPORT
>After 15 years, we finally have (October 1st) the full report of
>the U.S. National Cancer Institute (NCI) on the exposure of
>Americans to radioactive iodine [I(131)] from above-ground
>nuclear tests in the 1950s. In 1982, Congress ordered the NCI to
>investigate the population exposure following 90 nuclear tests at
>the Nevada test site 65 miles northwest of Las Vegas, and it was
>only this past August that a summary of results was finally
>released. These nuclear tests apparently already or will in the
>future cause as many as 75,000 additional thyroid cancers in the
>American population, primarily in those who were young children
>at the time. It is estimated that 70% of these cancers have yet
>to be diagnosed. The full report, evidently more than 100,000
>pages, has been made available on the Internet. Richard Klausner,
>director of the NCI, was sharply criticized last week by a U.S.
>Senate subcommittee for the delay in releasing the report. Ruth
>Faden, director of the Johns Hopkins Bioethics Institute, who
>chaired the President's Advisory Committee on Human Radiation
>Experiments, said, "The ground that's lost when, fairly or
>unfairly, a federal agency is perceived to be withholding
>information can be devastating." The average dose to Americans
>from all 90 tests was apparently 2 rads, with the high end dose
>of the order of 16 rads. QY: NCI Report: http://www.nci.nih.gov
>(Nature 9 Oct 1997)
>
>3. A WORKSHOP ON CHONDRITE METEORITES
>Chondrite meteorites are characterized by the presence of chondr-
>ules, small spherical inclusions of glassy rock that can be seen
>easily with the naked eye if the meteorite is cut and one of the
>cut faces polished. Carbonaceous chondrites contain both chondr-
>ules and volatiles, and since the presence of the volatiles is
>believed to indicate an origin which did not involve heat, the
>carbonaceous chondrites are considered the least altered remains
>of the solar nebula from which the planets are believed to have
>formed. In general, the study of chondrites is one of the
>important keys to the history of our solar system. One of the
>more interesting carbonaceous chondrites is the meteorite called
>Allende, which fell on 8 February 1969 at Pueblito de Allende in
>norther Mexico, and which scattered 5 metric tons of material
>over an area 48 kilometers long by 7 kilometers wide. Some 100
>meteorite specialists met recently at a workshop in Hawaii (the
>Workshop of the Nebular and Parent Body Alteration of Chondritic
>Materials, 17-19 July, Maui, HI US), with a major discussion of
>the present divergent views concerning the origin and formation
>of chondrites and how these views are related to current models
>of the early history of the solar system. The challenge for these
>meteorite specialists is to attempt to understand the complex
>record produced 4.56 billion years ago (a consensus date derived
>from isotope data), as evidenced in the microstructure of chondr-
>ites, when the meteorite formation events have no apparent
>terrestrial analog. The Allende meteorite was an important focus
>at this meeting, a meteorite that has "already stimulated and
>intrigued many planetary scientists for the last 25 years".
>QY: Adrian Brearley <brearley en unm.edu> (Science 3 Oct 1997)
>
>4. FRACTIONAL ELECTRONS IN CONDENSED MATTER PHYSICS
>Solid state physics, both experimental and theoretical, has been
>undergoing a transformation during the past decade, and if one
>must characterize the transformation it can perhaps be accomp-
>lished by saying there is now an entire domain of experimental
>observations in the condensed state that are best described by a
>new set of rules that for the time being are producing as many
>problems as solutions. What is involved is the so-called "fract-
>ionalization" of the electron, with the quantum theory of solids
>now possessing a considerable variety of fractionated electron
>entities: composite fermions, composite bosons, spinons, holons,
>heavy electrons, small polarons, and entities called "quasi-
>particles". Since all of these entities, including the fract-
>ional-charge electron, arise as theoretical explanations for
>experimental observations, one could make an argument that these
>entities are in effect virtual particles produced by special
>constraints on condensed systems, but evidently not all physic-
>ists would agree with the use of the term "virtual", and in fact
>the differences may be one of semantics, as was the early debate
>about the particle nature of semiconductor holes. What is
>important is that the physics of the condensed state is appar-
>ently in a fermentation stage, and we can expect that out of this
>fermentation will come a new physics with enormous practical
>applications. Philip W. Anderson (Princeton University, US), in a
>review of the history of the physics of the electron in condensed
>matter, emphasizes that study of electron fragility in the
>quantum Hall regime has been one of the great successes of the
>last decade, but the apparently simpler problem of the motion of
>spin-charge separated electrons in one- and two-dimensional
>systems is only beginning to yield to understanding. Anderson
>predicts the motion problem will be a solid problem for the next
>few decades. QY: P.W. Anderson, Princeton Univ., Physics (609)
>258-4400 (Physics Today October 1997)
>
>5. LONG RANGE ORDER IN STACKS OF FLUID MONOLAYERS
>In chemistry, elastomers are rubber-like substances, particularly
>polymers that show that behavior. A smectic elastomer is one that
>also show the behavior of a liquid crystal, a system in which the
>molecules are arranged in a series of layers, with the molecules
>in each layer being either ordered or randomly distributed. The
>term "liquid crystal" is applied because these systems can often
>be considered as crystals with liquid properties or as liquids
>with crystalline properties. A common example of a liquid crystal
>is the wall of a soap bubble. Another common example is the
>plasma membrane that surrounds biological cells. Concerning
>smectic elastomers that are polymers, one might expect that the
>liquid crystal behavior of such systems would be affected by the
>existence and degree of cross-linking between polymer chains, and
>in fact polymer chemists have demonstrated this, and the physical
>chemistry of cross-linked polymers in layers is an active field.
>Gerald C. L. Wong et al (5 authors, 3 installations in NL, US,
>DE) report a high-resolution x-ray diffraction study of a smectic
>elastomer (a polyacrylate species) that reveals the effects of
>weak cross-linking on long-range ordering of two-dimensional
>systems. They find the introduction of a random network of cross-
>links enhances the stability of the layered structure against
>thermal fluctuations, and induces one-dimensional long-range
>ordering at lengths up to several microns. What is interesting
>here is that the introduction of random cross-linking, which
>itself is disorder, has the counterintuitive result of promoting
>long range order of a smectic system. QY: Wim H. de Jeu
><dejeu en emolf.nl> (Nature 9 Oct 1997)
>
>6. A NEW APPROACH TO THE DE NOVO DESIGN OF PROTEINS
>An argument can be made that the unraveling of the mysteries of
>enzymes and other proteins will depend on the possibility of
>tinkering systematically with structure. Certainly that has been
>the thrust of much research aimed at relating structure to
>function. Until now, the primary method of tinkering has been
>genetic alteration, changing the gene that codes for a specific
>protein, hopefully in a manner such that the specific change in
>the protein is known, and then examining the effect of the change
>in protein structure on protein function. This is good tinkering,
>but not the best sort of tinkering. Ideally, one would want to be
>able to design and synthesize proteins, and then systematically
>examine the functions of various structural designs. Twenty years
>ago, that was a dream. These days, the dreams of molecular
>biologists are turning into reality at a breathtaking pace.
>Bassil I. Dahiyat and Stephen L. Mayo (California Institute of
>Technology, US) report the first fully automated folding design
>and experimental validation of a novel sequence for an entire
>protein. They used a computational design algorithm based on
>physico-chemical potential functions and stereochemical
>constraints to screen a combinatorial library of (1.9)10exp(27)
>possible amino acid sequences for compatibility with a particular
>folding design target. The authors suggest this result demonstr-
>ates that unbiased computational methods can successfully be used
>for protein design. QY: S. Mayo <steve en mayo.caltech.edu>
>(Science 3 Oct 1997)
>
>7. SPECIFICATION OF CELL AFFINITIES BY AN INTERCELLULAR SIGNAL
>Two of the major tasks of research in molecular embryology are
>1) to unravel the mechanisms that are responsible for the
>differentiation of cells into distinct cell types; and, 2) to
>explain how populations of distinct cell types conjoin to form
>specific tissues and organs. During the embryonic process, there
>are essentially two mechanisms possible for the conjoining of
>specific cell types into differentiated tissues: 1) intrinsic
>gene-based surface affinities between cells of each specific
>type, so that cells of each type will aggregate together and
>remain distinct from cells of another type; and, 2) external
>chemical signaling that produces chemical gradients that in turn
>produce different aggregations of different cell types. Isabel
>Rodriguez and Conrad Basler (University of Zurich, CH) report
>that the boundary that segregates Drosophila segmental primordium
>anterior and posterior compartment cells into adjacent but
>immiscible cell populations is mainly a consequence of local
>protein signalling (the so-called "hedgehog" protein) rather than
>due to an intrinsic affinity difference (mediated by the
><engrail> gene) between the anterior and posterior cells.
>QY: C. Basler <basler en zool.unizh.ch> (Nature 9 Oct 1997)
>
>8. NEW DATA AGAINST IMPORTANT TELOMERASE ROLE IN CANCER
>Telomeres are defined ends of chromosomes that contain specific
>repeated DNA sequences. They are essential for normal chromosome
>replication, and since their length shortens a bit with each
>replication, they are believed to be involved in the aging of the
>cell. Telomerase is an enzyme that repairs damage to telomeres,
>and it is thought by some that cancerous cells may have mutant
>telomerase, the mutant enzyme conferring immortality on the
>cancer cell. Now M. A. Blasco et al (Cell 91:25 1997) have
>genetically engineered telomerase-deficient mice and have shown
>that after 6 generations these mice are both viable and fertile.
>Commenting on this research, David Wynford-Thomas and David
>Kipling (University of Wales College of Medicine, Cardiff UK)
>suggest that telomerase inhibitors that have been envisaged for
>cancer therapy will therefore not have any acute toxicity against
>cancer cells or other cells. Blasco et al have suggested that
>current dogma that telomerase facilitates tumor growth may be
>wrong, with telomerase nothing more than a "passive bystander" in
>oncogenesis. (Nature 9 Oct 1997)
>
>9. ROLE OF KAINATE RECEPTORS IN SYNAPTIC TRANSMISSION
>L-glutamate (derived from the amino acid, glutamic acid) is
>considered the principal excitatory neurotransmitter in the
>vertebrate central nervous system, and is one of the neuro-
>transmitter substances that interact with ligand-gated ion
>channels. Kainic acid, an algal neurotoxin, is a structural
>analogue of glutamate, and it has been extensively used in
>research, since at high concentrations it selectively destroys
>glutamate receptor neurons (glutaminergic neurons). Glutamate is
>known to act on 3 classes of receptors, one of them called the
>kainate receptor because at low concentrations of kainic acid the
>action of glutamate on this receptor is enhanced. The chemistry
>of this kainate receptor is not yet well-characterized, mainly
>because selective ligands for it are not known. Now Vernon R. J.
>Clarke et al (15 authors at 5 installations in UK, CA, US),
>investigating the actions of a selective agonist (ATPA) and a
>selective antagonist (LY294486) of kainate receptor in the part
>of the brain called the hippocampus, report that those kainate
>receptors comprised of or containing glutamate-R-5 receptor
>(GluR5) subunits regulate synaptic transmission in the hippo-
>campus, with receptor activation depressing synaptic inhibition.
>The authors suggest this action by kainate receptors is consist-
>ent with the known epileptogenic effects of kainate.
>QY: V. Clarke, University of Bristol, Anatomy, UK.
>(Nature 9 Oct 1997)
>
>10. INCREASING U.S. PREVALENCE OF HERPES SIMPLEX VIRAL DISEASE
>Genital herpes (also called HSV-2) is a predominantly sexually-
>transmitted viral disease caused by the herpes simplex virus. The
>disease produces recurrent and often painful skin and internal
>lesions, and at the present time there is no cure and only limit-
>ed treatment with drugs (e.g., acyclovir). Douglas T. Fleming et
>al (7 authors at U.S. Centers for Disease Control and Emory
>University, US), examining serological studies of 1976 to 1980,
>and new serological studies of 1988 to 1994, report that the
>prevalence of HSV-2 infection in the U.S. has increased by 30%
>since the late 1970s, and HSV-2 antibody is now detectable in
>about 20% of the population over 12 years of age. The authors
>suggest that improvements in the prevention of HSV-2 infection
>are needed, particularly since such infections, via the genital
>ulcers produced, facilitate the transmission of the human immuno-
>deficiency virus (HIV), the pathogen in AIDS. QY: Michael E. St.
>Louis, CDCP, Mailstop E-02, 1600 Clifton Rd., Atlanta, GA 30333
>US (New England J. Med. 16 Oct 1997)
>
>---------------------------------------------
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---
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(No te rías, que te veo)
909-549-752

Las personas reales están repletas de seres imaginarios.