Consider another cell (top circle below). The cytosine shown in the middle of th
ID: 144061 • Letter: C
Question
Consider another cell (top circle below). The cytosine shown in the middle of the DNA sequence is a 5-methyl cytosine that has been deaminated (indicated by C*).
1. Which DNA damage repair system is designed to fix this type of damage?
i. Proofreading
ii. Base excision Repair
iii. Nucleotide Excision Repair
iv. Mismatch repair.
2. Again, let’s say that this damaged base is NOT fixed. Following two rounds of replication and cell division, four cells are made. Write out the genotypes you would expect within each cell at each cell division. (NOTE: C=cytosine, A=adenine, T=thymine, G=guanine and C*=cytosine that has been deaminated). Keep the top strand (plus strand) on top for each round of replication. Keep the bottom strand (minus strand) on the bottom.
Explanation / Answer
1. The type of DNA damage repair mechanism to fix the deaminated cytosine will be Base Excision Repair system. The repair is done by DNA glycolase and AP endonuclease which is followed by the DNA polymerase and DNA ligase acting on the gapped product.