BCH4024 - McKenna Lecture 56

BCH4024 - McKenna Lecture 56 - 1 Information Restructuring...

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Unformatted text preview: 1 Information Restructuring Last 2 Lectures L-50 DNA Damage and Repair < Responses to DNA damage Restriction & Modification > protection in prokaryotes > Reagents for Mol. Biol. Categories of DNA Repair L-51 Recombination - Redistribution of genome Homologous recombination Gene re-arrangements- transposition of DNA genome segments from distant region DNA AS A SUBSTRATE NOT A TEMPLATE DNA Damage and Repair- For RNA, protein & membrane phospholipids errors in synthesis or due to environmental factors can be minimized by turnover or replacement .-For DNA , information must be transmitted intact to daughter cells However Accuracy is maintained by: 1- High fidelity in replication- 3- exonuclease activity of DNA pol 1- Uracil-DNA N-glycosylase pathway (corrects mutations from deamination of cytosine - see later ) 2-Mechanisms for correcting genetic info. in damaged DNA , e.g due to chemical mod or photochemical changes (high energy radiation) 2 Mis-incorporation of bases (spontaneous) Cancer Deamination cytosine to Uracil Depurination (hydrolysis of glycosidic bond) UV light radiation damage pyrimidine dimers Oxidation by hydroxyl radicals Single and double strand breaks Alkylation Methylation is also an important biological process Examples of DNA DAMAGE DNA METHYLATION-Methylation underlies several important biological processes: 1. Restriction and modification- Prokaryotes 2. Mismatch error correction ( a DNA repair process )- Prokaryotes 3. The control of eukaryotic gene expression in Eukaryotes-S-Adenosylmethionine (AdoMet) is the substrate for methylation of both RNA and DNA. A methyl group is transferred to a nucleotide. Unstable sulfonium ion Parental strands are tagged (Activated Met donates CH 3 ) 3 DNA METHYLATION- occurs at the polynucleotide level- S-adenosylmethionine is methyl donor (activated derivative of methionine) -Reaction is a transmethylation- RNA or DNA 5-Methyl cytosine sole methylated base in eukaryotes (+ Thymine )- occurs at CpG sequences- animals N 6- methyladenine & CpN pCp in plants-found in prokaryotic DNA The methylation pattern of DNA is maintained when DNA is replicated! Adenine CH 3 S ribose CH 2 CH 2 HC NH 3 COO- + + S-adenosyl- homocysteine CH 3 CH 3 CH 3 In prokaryotes N 4- methyl cytosine 5-GATC-3 Structure of DNA-Methylase ( Hha ) Complex (1994) X-ray Enzyme -Loops containing catalytic site in white - rest in orange...
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This note was uploaded on 03/15/2010 for the course BCH 4024 taught by Professor Allison during the Spring '08 term at University of Florida.

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BCH4024 - McKenna Lecture 56 - 1 Information Restructuring...

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