Lecture.20.Fall.2013

Damage the bases these reactive forms of oxygen

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Unformatted text preview: en=most free radicals • Reactive forms of oxygen (free radicals) are produced in the course of normal aerobic metabolism, as well as by radiation, ozone, peroxides, and certain drugs. damage the bases • These reactive forms of oxygen damage DNA and induce mutations by bringing about chemical changes to DNA. Radiation • In 1927, Hermann Muller demonstrated that mutations in fruit flies could be induced by X-rays. • Ionizing radiation, including X-rays, gamma rays, and cosmic rays, can penetrate tissues and damage DNA. • High-energy radiation Radiation • High-energy radiation dislodges electrons from atoms, changing stable molecules into free radicals and reactive ions. • Alters the structures of bases and breaks phosphodiester bonds in DNA. • Also results in double-strand breaks in DNA. • Ultraviolet (UV) light has less energy, but is still mutagenic. ionizing radiation causes translocations/deletions UV light causes pyrimidine dimers, which block replication covalent bonds between adjacent pyrimid this cannot happen, causes a stall and no repair introduces errors and cause mutations • Error-prone repair mechanisms must be used to bypass these blocks (a bit more on this later). • These save the cell from death, but introduce errors in the base sequence. Mutational (Genetic) Analysis • The study of the function of genes through examination of the results of mutation • How do you identify mutants? look at phenotype/identify a phenotype depends on organism Bacteria and Fungi wild type org • Mutagenize prototrophs (can grow on minimal medium) • Screen for strains that can grow on complete, but not minimal, medium Fruit Flies (Drosophila melanogaster) • Visible mutations (developmental) • S...
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This document was uploaded on 02/25/2014.

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