Each of the following DNA fragments has exactly one thing wrong with it. Indicat

Question

Each of the following DNA fragments has exactly one thing wrong with it. Indicate a) what is wrong with the fragment, b) a possible source of the problem, c) which DNA repair mechanism(s) are necessary to completely repair the problem, and d) what the correct DNA sequence should be. For all examples, assume the top strand to be the template strand. In the last example, assume T=T is a thymine dimer, and A-A is a normal continuation of the DNA sequence.

5’-ACGTCGATACTGCGATCTGACGTACTGACGACTG-3’

3’-TGCAGCTATGACGCTA ACTGCATGACTGCTGAC-5’

Explanation / Answer

Given strand is the double stranded DNA whose strands are complementary to each other. By comparing both the strands we can easily answer all the questions.

A- in the bottom one nucleotide is missing which is Guanine.

B- Guanine from the bottom strand is missing due to the spontaneous hydrolytic cleavage of the Guanine from the strand. Cleavage creates the Apurinic site or Baseless site.

C- base excision repair mechanism will repair the apurinic site which is created due to hydrolytic cleavage. DNA polymerase and DNA ligase enzyme help in this process.

D- Missing Guanine has been bold and underlined

TGCAGCTATGACGCTA G ACTGCATGACTGCTGAC-

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