The following nucleotide sequence is found in a short stretch of DNA: 5’ – ATGT

Question

The following nucleotide sequence is found in a short stretch of DNA:

5’ – ATGT – 3’

3’ – TACA – 5’

If this piece of DNA is exposed to a chemical that will deaminate just cytosines, let us consider what the effect will be upon this sequence.  

1. What DNA sequences will result if DNA repair machinery does not work?

a. If this stretch of DNA is not methylated?

b. If this stretch of DNA is methylated?

2. What sequences will result if DNA repair machinery does work?  Which DNA repair will be used to fix the deaminated base and how?

a. If this stretch of DNA is not methylated?

b. If this stretch of DNA is methylated?

Explanation / Answer

when cytosine is metylated the deamination will not alter the structure when the cytosince is unmethylated the DNA structure will be altered.

2a cytosine will be replaced by uracel

this is used to study methylation in genes mostly at transcription start sites of promoter regions to check if the gene is on or off state

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