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’-ATCATACTGCATGCAT=TACTGACGAGTCATCTAC-3’

3’-TAGTATGACGTACGTA-ATGACTGCTCAGTAGATG-5’

Explanation / Answer

Problem is of thymine dimer.

T=T dimers may be repaired by two mechanisms. (a) In photoreactivation repair, the PRE enzyme activated by blue light breaks the dimer, restoring the normal base pairing. Note that blue light can affect DNA because it is at the same end of the spectrum as UV radiation. (b) In excision repair, the uvr system excises the dimer, and the gap is filled in by the proof-reading activity of DNAPol I.

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