Question

One of the DNA parental strands is 5’ ACCTCATCG 3’. The Boldface C was deaminated(and the mutation was not repaired). This strand does not get transcribed, the other one does.

a) Predict the double stranded sequence of both dsDNA molecules made after one round of replication. Label the parental vs daughter strands in each ds molecule

b) For each dsDNA mol (in part a) predict the RNA sequence if transcription occurred.

Answer 1

The given parental strand is 5’ ACCTCATCG 3’ where C was deaminated and not repaired.

As we know that deamination of cytosine (C) forms uracil (U) and uracil forms double bond with adenine (A) and the effect of the mutation will be seen in the next round of replication but not in the parental strand.

a) So the dsDNA molecule is as follows.

Parental strand 1: 5’ ACCTCATCG 3’

Parental strand 2: 3' TGGAGTAGC 5'

After one round of replication the result would be like the following ude to the incorporation of U in C position.

Parental strand 1: 5’ ACCTUATCG 3’

Daughter strand 1: 3' TGGAATAGC 5'

Parental strand 2: 3' TGGAGTAGC 5'

Daughter strand 2: 5' ACCTCATCG 3'

b) The RNA sequence produced are as follows.

From, parental strand 1 and daughter strand 1 is 5' ACCUUAUCG 3' (mutated RNA transcript).

From, parental strand 2 and daughter strand 2 is 5' ACCUCAUCG 3' (Normal RNA transcript).