080818.PMCB.lecture.2.DNArepair

080818.PMCB.lecture.2.DNArepair - 1 lant Molecular and...

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Unformatted text preview: 8/20/2008 1 lant Molecular and Cellular Biology Lecture 2: Mechanisms of DNA Repair Gary Peter 8/20/2008 PMCB Lecture 4: G. Peter 2 Learning Objectives 1. Explain the role for DNA repair in high- fidelity DNA replication 2. Describe the structures and functions of enzymes responsible for DNA repair 3. Explain their roles in DNA repair 4. Explain the in vitro applications of DNA repair enzymes for recombinant DNA methods 8/20/2008 PMCB Lecture 4: G. Peter 3 Mutations and DNA Repair z Mutations occur if the DNA is not repaired z The damage that occurs is usually to one-two bases on one strand, thus the opposite strand provides the template for insertion of the correct base 8/20/2008 PMCB Lecture 4: G. Peter 4 Overview of DNA Repair z DNA repair is essential for survival z 5,000 purine bases are lost per cell per day from thermal fluctuations z Increases fidelity of DNA replication by ~100 fold over DNA polymerases 8/20/2008 PMCB Lecture 4: G. Peter 5 Common Steps in Repair Pathways z Recognition of the altered base z Facilitated by structure of double helix z Removal of alteration z Synthesis of correct nucleotide z Facilitated by the structure of double helix & sister chromatids z Some exceptions occur here: direct reversal, nonhomologous end joining, error prone DNA repair 8/20/2008 PMCB Lecture 4: G. Peter 6 ommon Forms of amage to Bases in DNA z The glycosidic bond of nucleotides is prone to acid-catalyzed hydrolysis to form abasic sites z ~10,000 abasic sites per human cell per day (10,000/3x10 9 = 1 in 3 x 10 5 bases) z Detection and repair of damaged bases is facilitated by the structure of DNA 8/20/2008 PMCB Lecture 4: G. Peter 7 Direct Reversal z Two types of altered bases can be directly reversed z O6-alkylguanine adducts are directly removed by O6-alkylguanine transferases z Pyrimidine dimers induced by UV light are directly reversed by photolyases 8/20/2008 PMCB Lecture 4: G. Peter 8 irect Reversal of Damaged Bases: 6-alkylguanine Transferase z In most organisms, O6- alkylguanine adducts can be repaired by alkylguanine transferases (AGT) z AGTs transfer the alkyl group from the altered guanine base in the dsDNA to a reactive cysteine group in an irreversible reaction Angew. Chem. Int. Ed. 2003, 42, 2946 – 2974 The EMBO Journal Vol. 19, pp. 1719-1730, 2000 8/20/2008 PMCB Lecture 4: G. Peter 9 Direct Reversal of Damaged Bases: Photolyases z UV-induced pyrimidine dimers (cyclobutane pyrimidine dimers) can be repaired by nucleotide excision (mammals) or by direct reversal of the damage by photolyases in plants, lower eukaryotes, and bacteria z Photolyases contain a chromophore which absorbs light and transfer of the excitation energy to the FAD cofator for electron transfer to the pyrimidine dimer to initiate the reversion Current Opinion in Chemical Biology 2001, 5 :491–498 8/20/2008 PMCB Lecture 4: G. Peter 10 Base Excision Repair: DNA Glycosylases z Damage to DNA bases from deamination, oxidation, demethylation and alkylation is mainly repaired...
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This note was uploaded on 05/31/2011 for the course PCB 5530 taught by Professor Peter,g during the Spring '08 term at University of Florida.

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080818.PMCB.lecture.2.DNArepair - 1 lant Molecular and...

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