How does DNA error takes place?

Asked by vidyatmika | 3rd Feb, 2010, 11:23: AM

Expert Answer:

While most DNA replicates with fairly high fidelity, mistakes do happen, with polymerase enzymes sometimes inserting the wrong nucleotide or too many or too few nucleotides into a sequence. Fortunately, most of these mistakes are fixed through various DNA repair processes. But some replication errors make it past these mechanisms, thus becoming permanent mutations. These altered nucleotide sequences can then be passed down from one cellular generation to the next, and if they occur in cells that give rise to gametes, they can even be transmitted to subsequent organismal generations. Moreover, when the genes for the DNA repair enzymes themselves become mutated, mistakes begin accumulating at a much higher rate.

It is suspected that most DNA replication errors are caused by mispairings: either between different but nontautomeric chemical forms of bases or between "normal" bases that nonetheless bond inappropriately because of a slight shift in position of the nucleotides in space. This type of mispairing is known as wobble. It occurs because the DNA double helix is flexible and able to accommodate slightly misshaped pairings.

 

Replication errors can also involve insertions or deletions of nucleotide bases that occur during a process called strand slippage. Sometimes, a newly synthesized strand loops out a bit, resulting in the addition of an extra nucleotide base. Other times, the template strand loops out a bit, resulting in the omission, or deletion, of a nucleotide base in the newly synthesized, or primer, strand. Regions of DNA containing many copies of small repeated sequences are particularly prone to this type of error. Also a mutation could occur that produces repeats of some of the bases.

Answered by  | 9th Feb, 2010, 08:36: AM

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