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Biotech / Medical : Sugen (SUGN) -- Ignore unavailable to you. Want to Upgrade?

To: gao seng who wrote (519)	7/20/1999 12:01:00 PM
From: gao seng	Read Replies (1) \| Respond to of 550

What are the types of radiation? X rays, of course. Are they different that UV radiation? Are electromagnetic fields considered radiation? Which type of radiation is used to treat cancer? Anyway, an interesting article on the genesis of [skin] cancer: UV Rays Change DNA To Lead To Skin Cancer Researchers at Georgia Tech have developed a model system that mimics how solar ultraviolet (UV) light damages cellular DNA. The model helps explain, in molecular detail, one of the biochemical changes that lead to skin cancer. In the laboratory, exposing a specially-modified DNA fragment to UV radiation generates a positively-charged ion that disrupts the DNA's structure, according to the authors of the article in today's Proceedings of the National Academy of Sciences. The ion's microelectric charge travels along the chains of bases that comprise DNA -- adenine, cytosine, guanine and thymine. Initially, the ion causes DNA base pairs to compress, moving close enough together to become electrically conductive. Then the DNA bases act as a wire and relay the charge down the line, temporarily holding the charge before passing it onto neighboring bases. In the PNAS article, the authors identify this mechanism as "phonon-assisted polaron-like hopping." The idea that DNA can facilitate a charge relay has been contemplated for more than 35 years, but only recently has it been documented that the relay stops when the charge reaches a spot where two guanine (G) bases are located side by side. Damage is more likely to occur if the ion is introduced into the DNA at a location that is very close to the G-G bases, the authors report. Instead of passing the charge along, the two guanine bases trap the ion and incorporate it into their structure. The ion then causes the DNA to become chemically unstable, and the DNA chain breaks. A break in what is otherwise a continuous molecule can have enormous biological ramifications, such as inducing mutations that lead to cancerous cell growth. (Similar breaks also can be induced by chemically-produced ions, and may be the mode of action for some chemical carcinogens, the authors note.) The authors add that an appealing aspect of their model is that "it can be generalized to reconcile experimental and theoretical findings that previously seemed contradictory." Co-authors, all from the School of Chemistry and Biochemistry of the Georgia Institute of Technology, include Paul T. Henderson, Denise Jones, Gregory Hampikian, Yongzhi Kan and Gary B. Schuster. The research was supported by grants from the National Institutes of Health (NIH) and the National Science Foundation (NSF). [Contact: Gary B. Schuster] 20-Jul-1999 Main Entry: X ray Pronunciation: 'eks-"rA Function: noun Date: 1896 1 : any of the electromagnetic radiations of the same nature as visible radiation but having an extremely short wavelength of less than 100 angstroms that is produced by bombarding a metallic target with fast electrons in vacuum or by transition of atoms to lower energy states and that has the properties of ionizing a gas upon passage through it, of penetrating various thicknesses of all solids, of producing secondary radiations by impinging on material bodies, of acting on photographic films and plates as light does, and of causing fluorescent screens to emit light 2 : a photograph obtained by use of X rays Main Entry: ultraviolet Function: adjective Date: 1840 1 : situated beyond the visible spectrum at its violet end -- used of radiation having a wavelength shorter than wavelengths of visible light and longer than those of X rays 2 : relating to, producing, or employing ultraviolet radiation - ultraviolet noun Main Entry: far ultraviolet Function: adjective Date: 1947 : of, relating to, or being the shortest wavelengths of radiation in the ultraviolet spectrum and especially those between 100 and 300 nanometers