GeneticsHWchapter16B - Questions for Chapter 16B Material...

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Questions for Chapter 16B Material C32. During methyl-directed mismatch repair, why is it necessary to distinguish between the template strand and the newly made daughter strand? How is this accomplished? It is necessary to distinguish between the template strand and the newly made daughter strand so you can find the strand with the mismatched base. The template strand is methylated because that’s how normal DNA is, and since it can’t be copied during replication the new strand is not methylated for a short while after replication. MutS recognizes the mismatch, and mutH endonuclease recognizes the unmethylated strand, nicks it at the methyl site, and an exonuclease removes mismatched nucleotides. DNAP111 and ligase also play their normal roles in ths process. C38. What is the underlying genetic defect that causes xeroderma pigmentosum? How can the symptoms of this disease be explained by the genetic defect? There is no underlying genetic effect that causes XP because the UvrABC endonuclease is made up of three different subunits produced by 3 different genes and requires a special helicase to remove the nicked fragment. So theres a chance the mutation causing XP is in any one of those 4 genes. Since they cant fix dimmers produced by UV radiation from the sun, people with XP are much more likely to get skin cancer than those who don’t have it. A1. Differentiate between a DNA lesion and a mutation.
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GeneticsHWchapter16B - Questions for Chapter 16B Material...

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