Question

Answer all the list questions below. Provide reasoning for the identified correct answer. Also, provide reasoning for the invalid answers.

I will thumb you down if you do not follow the above instructions completely

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25) Which of the following is false regarding mis-match repair?

a) It is initiated by specific proteins that function in sequential steps, not as a singular large complex

b) It is the same mechanism as recombination repair

c) It involves DNA ligase

d) It involves DNA polymerase 5’ to 3’ activity

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32) A relatively small circular DNA molecule that encodes oncogenes and is present in many types of cancer is called a _____.

a) double second

b) double minute

c) mitochondrial DNA

d) pseudogene

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34) Which of the following is true regarding p53 accumulation in cells?

a) p53 exists in greater levels and is more active in unstressed cells as compared to stress/damages cells.

b) Phosphorylation and acetylation are involved in allowing p53 to act as a transcription factor

c) Ubiquitination is involved in allowing p53 to act as transcription factor

d) MDM2 binds the C terminal end of p53 protein

Answer 1

25. Answer b) It is the same mechanism as recombination repair.

In recombination repair, impaired nucleotide sequences are exchanged between two similar or identical molecules of DNA whereas mismatch repair is involved in repairing erroneous insertion, deletion, and mis-incorporation of bases.

Mismatch repair is initiated by specific proteins like MutS, MutL and MutH that function in sequential steps. Mismatch repair involves 5' to 3' polymerase activity of DNA pol III to repair the gap which uses the other strand as a template, and finally sealed by DNA ligase.

32. answer d) psuedogenes.

They are segments of DNA related to real genes and have lost some functionality when compared to real genes.They result from multiple mutations in genes whose product is not required for the survival of the organism. Pseudogenes are involved in cancers. For example a pseudogene BRAF is a protooncogene and is present in many cancers in mutated condition.

34) Answer b) Phosphorylation and acetylation are involved in allowing p53 to act as a transcription factor

Under stress/ damaged conditions of cells, p53 is  activated to prohibit the replication of cells containing damaged DNA. When MDM2 binds to p53, its results in ubiquitination of p53 in the cytoplasm. But when the cell is under stress, p53 is phosphorylated and acetylated. This prevents MDM2 mediated degradation of p53 and p53 acuumulates in the nucleas where it acts as a transcriptional activator.