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05 Mutations and DNA repair mechanism

Mutations due to physical agents in the form of high

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Unformatted text preview: due to PHYSICAL AGENTS in the form of high energy radiation UV light leading to the formation of THYMINE DIMERS (covalent linkage of 2 adjacent thymines on the same strand of DNA) which can block DNA replication or interfere with base pairing. Ionizing radiation such as X-rays leading to single and double-stranded DNA breaks or to the formation of OH-radicals from water B. Mutations due to CHEMICAL / ENVIRONMENTAL SUBSTANCES BASE ANALOGUES - have similar structures to the DNA bases - more prone to tautomeric shifts 5-Bromouracil is a structural analogue of thymine. It undergoes tautomeric shift to base pair with guanine instead of adenine. Example: 5-Bromouracil ALKYLATING AGENTS -adds a methyl or ethyl group to a base -the largest class of “potential” mutagens present in man’s environment example: N-nitrosoamines (found in cigarette smoke) When N-nitrosoamine is in the liver, it is metabolized by liver enzymes to form alkylating agents which can attack Guanine. There are 2 reactive sites in G, the N7 and O6 positions. If...
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