Question

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to ____________. If the adenosine in the sequence TCAT is depurinated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication?

1) TCGT
2) TAT
3) TCT
4) TGTT

Answer 1

Unrepaired depurination before DNA replication can lead to a point mutation in the daughter DNA strands, leading to the sequence TAT after two rounds of replication if an adenine base in sequence TCAT is lost.

Step-by-step explanation:

When DNA damage such as depurination occurs before DNA replication and is not repaired, it can result in mutations after DNA replication. If the adenosine (A) within the sequence TCAT is depurinated and not repaired, there would be a missing base in that position. After two rounds of replication, the expected result would be option 2) TAT, since no new base would be added opposite the site where the adenine was lost in the first replication, and the same would happen in the second round of replication.

Depurination is specifically the loss of a purine base such as adenine or guanine from DNA. DNA replication without repair can incorporate mistaken bases, which daughter cells will inherit, making these mutations permanent unless a rare back mutation occurs. Thus, depurinated adenosine that is not repaired before replication can lead to a point mutation in the daughter DNA strands. These unintended changes to DNA caused by factors like radiation, chemicals, or spontaneous reactions can lead to various types of mutations, such as base insertions or deletions.