Chemical Education Today
Reports from Other Journals
Nature: What Matters in Nature—DNA, Light-Driven Ion Pumps, and Antimatter by Sabine Heinhorst and Gordon Cannon
DNA at 50 Fifty years ago (April 25, 1953), James Watson and Francis Crick announced the elucidation of the structure of DNA in an article in Nature that is barely more than a page long, cites a total of six references, and features as its only figure an outline of the DNA double helix drawn by Crick’s wife, Odile. The article begins with the sentences “We wish to suggest a structure for the salt of deoxyribonucleic acid (D.N.A.). This structure has novel features which are of considerable biological interest.” and ends with the now famous “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”
graphic: Devens Gust Figure 1. The photoinduced pumping of calcium ions across a lipid bilayer. Absorption of light by the porphyrin (green oval) leads to charge separation that yields a negatively charged naphthoquinone portion (blue hexagon) and a positively charged carotenoid moiety (orange ellipse) of the artificial reaction center. As a consequence, the quinone calcium carrier is reduced at the exterior surface and chelates Ca2+. Then the chelate diffuses across the bilayer. When it reaches the interior surface, the chelating ligand is re-oxidized and releases the Ca2+. As a result, Ca2+ ions are transported across the membrane through a light-driven process.
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This seminal scientific contribution correctly predicted the connection between structure and function of DNA and thereby heralded the advent of the molecular biology revolution. Watson and Crick’s discovery is appropriately commemorated on Nature’s Web site through a special link at http://www.nature.com/nature/dna50/ that provides free access to reprints of this and other related 1953 articles, such as those reporting the results of Maurice Wilkins’s and Rosalind Franklin’s X-ray diffraction studies establishing the helical nature of DNA’s secondary structure. Commentaries, personal accounts, and reviews by prominent researchers whose work throughout the years has helped to shape our current picture of our genetic material guide the viewer through the path DNA research has taken from its beginnings in the first half of the 20th century to the present genomics era. This Web feature is a boon not only for science history buffs but also will be appreciated by students and teachers alike. A Photon-Powered Calcium Pump Borrowing from known biological light-driven membrane transport systems, collaborators from Arizona State University and from Universidad National de Rio Cuarto, Argentina developed a nanoscale device that can perform photoinduced calcium transport across a lipid bilayer (2002, 420, November 28, 398–401). The liposomes prepared by the researchers feature a membrane-soluble quinone that chelates Ca2+ in its reduced (hydroquinone) form and releases the bound ion when oxidized. In addition, a synthetic light receptor asymmetrically inserted into the membrane absorbs visible light through its central porphyrin moiety. This leads to electron transfer and charge separation, thereby creating a negatively charged naphthoquinone radical anion end of the molecule near the external surface of the liposome and a carotenoid radical cation on the other end pointing towards the liposome’s interior. The naphthoquinone reduces calcium shuttle molecules near the exterior side of the bilayer, which results in Ca2+ uptake from the aqueous surroundings and release into the liposome interior as the shuttle molecule is being oxidized by the carotenoid radical cation moiety of the artificial reaction center. The authors show that the transport is specific for calcium ions, requires light, and proceeds against a concentration gradient. Despite its very low quantum yield (1%), this artificial transmembrane pump is able to generate a considerable membrane potential. Cold Anti-hydrogen The announcement that the ATHENA team at the European Center for Nuclear Research (CERN) in Geneva, Switzerland had generated cold anti-hydrogen atoms made a
Journal of Chemical Education • Vol. 80 No. 5 May 2003 • JChemEd.chem.wisc.edu
big splash in the scientific community (2002, 419, October 30, 456–459; see also the News and Views article on pp 439– 440). Although anti-particles have been around for a while, the ATHENA group has found a way of extending the lifetime of the anti-matter that should make an analysis of its properties possible in the future and thereby prove—or disprove—CPT invariance, the central theorem of quantum mechanics. The anti-hydrogen atoms were formed by mixing anti-protons and positrons after slowing the particles’ movement by electric fields and by exposure to near absolute zero temperatures (15 K). Since anti-matter and matter annihilate into a burst of energy upon encountering each other, contact of the charged anti-particles with the walls of the chamber had to be prevented by controlling their paths with magnetic fields in a device called a Penning Trap. When an anti-proton and a positron collide, an anti-hydrogen atom forms that is comprised of a negatively charged nucleus (anti-
proton) and a positively charged anti-electron (positron). Since their lack of charge prevents regulation of their movement by magnetic fields, the anti-hydrogen atoms quickly collide with the walls of the chamber. The ensuing mass annihilation provides the proof for the existence of an anti-hydrogen atom through detection of its characteristic pion and gamma ray products and retracing of their paths to a coincident origin. We would like to mention the excellent Web sites of CERN (http://public.web.cern.ch/public/) and the ATHENA project (http://athena.web.cern.ch/athena) that provide valuable information about anti-matter (for example, see FAQs) and particle generators and decelerators at CERN. Sabine Heinhorst and Gordon Cannon are in the Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 39406-5043; email:
[email protected] and
[email protected].
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