Question

A deamination occurs on the cytosine residue in the following DNA sequence. This cytosine residue happens to be methylated on the 5-position of the aromatic ring.
5'-GAATCG-3'
(Note: the top strand is shown; this is the strand where the deamination occurs.) If the mutation is not repaired, and a round of DNA replication occurs, then the sequence of the newly-replicated complementary strand (i.e., the bottom strand) will be:
A. 5-CAATTC-3'
B. 5'-CGATTC-3
C. 5'-GAATCG-3
D. 5'-GAATTC-3
E. None of the above

Answer 1

Answer:

A. 5-CAATTC-3'

Explanation:

Due to the spontaneous mutation of the cytosine, becoming uracil, the change in the new complementary strand would occur as follows:

5'-GAATCG-3 '-> Cytosine deamination = 5'-GAATUG-3' -> the new replicated complement is = 5-CAATTC-3 '

Remembering that Uracil equals a thymine in DNA, for that reason the mutated uracil base becomes Adenine when its synthesized in the new strand