Friday, March 23, 2007

Coping with Deamination

Deamination involves the removal of an amine group from a molecule. Maintaining the integrity of DNA can involve subtle strategies. When cytosine is deaminated uracil is the end result. Uracil is found in RNA but its DNA counterpart is thymine. The effect of this is to facilitate mismatch repair.

Before a repair mechanism is set in motion there must be a means of recognizing a mistake. That is much easier to do when the presence of uracil itself is an indicator. Uracil cannot be an indicator in RNA because it is a base unit needed to store and transmit genetic information i.e. it has a legitimate function that would be eliminated along with any uracil resulting from deamination.

An effect of deamination is to disrupt normal base pairing. Since cytosine is paired with guanine a change of cytosine to uracil would also involve a change in base pairing; uracil and thymine being paired with adenine. A change in templates can cause changes in the amino acid content of proteins. The simple substitution of thymine for uracil eliminates many problems.

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