Lect 24 - ©2003 C. Brachmann 1 DNA Repair and Cancer...

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Unformatted text preview: ©2003 C. Brachmann 1 DNA Repair and Cancer Genetics Bio Sci 97 Lecture 24 Dr. Carrie Brachmann Department of Developmental and Cell Biology [email protected] ©2003 C. Brachmann 2 Outline • The Genetic Code • Mutations • Types of mutations • Types of mutagens • DNA repair ©2003 C. Brachmann 3 Mutations • Fine-scale mutations can be due to: – Base substitutions, deletions, insertions, duplications • Effect of mutation on gene function: – Loss of function, hypomorph, hypermorph, gain of function – Mutation doesn’t have to be in protein-coding region to affect gene function • When mutation in protein-coding region: – Silent (substitutions), nonsense (substitutions), missense (substitutions), frameshift (duplications/deletions) ©2003 C. Brachmann 4 Mutagens • Cause DNA damage – Intrinsic mutagens-spontaneous – Extrinsic mutagens-increases the chances of mutation. Any kind of mutation that can be induced by an extrinsic mutagen can also occur spontaneously • DNA damage can generally be repaired – Repaired perfectly--no mutation – “Fixed”, repaired, but not to the original state, results in a mutation ©2003 C. Brachmann 5 DNA damage: damage from within (intrinsic) • Replication errors (i.e. genetic instability) • Recombination errors • Transposable Elements-moving or not • Water “a mammalian cell loses 10,000 purines from its DNA in 20 hours” • Respiration leads to oxidative damage ©2003 C. Brachmann 6 DNA damage: damage from outside (extrinsic) In general, DNA damage from extrinsic sources is stereotypical. One sort of mutagen causes a certain type of DNA damage • UV irradiation from sun – DNA absorbs energy, results in covalently joined thymine dimers. This distorts the helix, blocks replication and transcription. •Ozone (O 3 ) blocks UV • UV exposure inc’s risk of skin cancer by inc’g mut’n rate • Xeroderma pigmentosum ©2003 C. Brachmann 7 DNA damage: damage from outside (extrinsic) • Ionizing radiation (X and gamma rays, beta and alpha particles) – React with water or living tissue to form highly reactive ions called free radicals. These cause DNA strand breaks ==>inversions, deletions, translocations... • X rays—diagnostic, from TV… • Radon gas—from ground • Cosmic rays—more when you fly • nuclear tests—small % H&J Table 7.5 ©2003 C. Brachmann 8 DNA damage: damage from outside (extrinsic) • Chemical mutagens – any kind of mutation that can be induced by a mutagen can also occur spontaneously – geneticists use mutagens to increase the number of mutants for study – “many environmental contaminants are mutagenic, as are numerous chemicals found in tobacco products.” ©2003 C. Brachmann©2003 C....
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This note was uploaded on 04/15/2008 for the course BIO SCI 98 taught by Professor Goulding during the Spring '08 term at UC Irvine.

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Lect 24 - ©2003 C. Brachmann 1 DNA Repair and Cancer...

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