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’-GCATGACTGACTGCGCTGAGTCATGACGTCAGTC-3’

3’-CGTACTGACTGACGCGACTCAGTAUTGCAGTCAG-5’

Explanation / Answer

Answer:

a) what is wrong with the fragment:

In the given DNA fragment, there is a uracil nucleobase in the 3'-5' sequence:

5’-GCATGACTGACTGCGCTGAGTCATGACGTCAGTC-3’

3’-CGTACTGACTGACGCGACTCAGTAUTGCAGTCAG-5’

b) a possible source of the problem:

DNA may contain a Uracil as a result of deamination of cytosine. Deamination of cytosine causes mutation from C to U (Uracil). This leads to a mutagenic U : G mispairs.

c) which DNA repair mechanism(s) are necessary to completely repair the problem

Repair mechanism: Base excision repair process.

d) what the correct DNA sequence should be

In the correct sequence, Cytosine should pair with Guanine in DNA instead of Uracil

5’-GCATGACTGACTGCGCTGAGTCATGACGTCAGTC-3’

3’-CGTACTGACTGACGCGACTCAGTACTGCAGTCAG-5’

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