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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
• 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
• Screen for strains that can
grow on complete, but not
minimal, medium Fruit Flies (Drosophila melanogaster) • Visible mutations
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