topic 7 f 14.5 klug 14.1-14.4, 14.6-14.7, 16.2

topic 7 f 14.5 klug 14.1-14.4, 14.6-14.7, 16.2 - Emily Lin...

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Emily Lin 3/16/11 Topic 7 F 14.5; and Klug 14.1-14.4; 14.6-14.7; 16.2 14.5 discusses proofreading and also repairing mistakes and damage during and after synthesis is complete by enzymes. DNA polymerase is selective due to base pairing of nitrogenous bases and only inserts an incorrect deoxyribonucleotides once every 100,000 bases. From mutant E. coli with mutation localized to a particular portion of the ends of DNA strand polymerase III enzyme which acts as an exonuclease, which removes DNTs from ends of DNA in the 3’ to 5’ direction, only if they’re not H-bonded to a base on the complementary strand. Thus, if a wrong base is added during DNA synthesis, the DNA polymerase III pauses, removes the mismatched base and proceeds with synthesis. If DNA polymerase leaves a mismatched pair behind in the DNA sequence by mistake, a battery of enzymes spring up to correct the problem. Proteins responsible for mismatch pair repair after DNA synthesis is complete were also discovered through E. coli mutants. Genes are under assault of chemicals like hydroxyl, aflatoxin B1, radiation and UV rays after synthesis. Thymine dimers are an example, and create kinks in secondary structure of DNA, which stall movement of the replication fork. If damage isn’t repaired, cells may die. Thus, they have nucleotide excision repair, which has repair proteins recognize damaged bases and enzymes remove single stranded DNA around the damaged site
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This note was uploaded on 03/04/2012 for the course BIO 142 taught by Professor Escabar during the Spring '08 term at Emory.

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topic 7 f 14.5 klug 14.1-14.4, 14.6-14.7, 16.2 - Emily Lin...

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