One of the most common spontaneous lesions that occurs in DNA under physiological conditions is the hydrolysis of the amino group of cytosine, converting the cytosine to uracil. What would be the effect on DNA structure of a uracil group replacing cytosine?

A base substitution of G:C to A:T after two rounds of replication

A base substitution of G:C to A:C after two rounds of replication

A base substitution of G:C to U:T after two rounds of replication.

A base substitution of G:C to U:C after two rounds of replication.

The correct answer is "A base substitution of G:C to A:T after two rounds of replication".

Explanation:

Since one of the most common spontaneous mutations of DNA that occured naturally is the conversion of cytosine to uracil, the cells have a specific DNA repair system for the substitution of uracil in DNA. It works by the action of Uracil-DNA glycosylases (UDGs). UDGs in the first round of replication will remove the uracil found in the DNA. By the second round of replication thymine-replacing uracils will be reincorporated during repair synthesis. Due to the original nucleotide was a cytosine and at the end of the repair system is substituted with a thymine, the result is a base substitution of G:C to A:T after two rounds of replication.