Question

You are looking at an illustration depicting the process of telomere addition. Which enzyme is most likely to be found on the illustration:

		DNA dependent RNA polymerase
		RNA dependent DNA polymerase
		DNA dependent DNA polymerase
		Reverse transcriptase

Answer 1

RNA dependepent DNA polymerase (or reverse transcriptase)

Telomeres are the tips of chromosomes in linear eukaryotic chromosomes. They contain repeatitive sequences added by enzyme telomerase after the process of DNA replication.

In eukaryotes, having linear chromosomes, after every round of DNA replication, the ends of the chromosomes get shortened. If this continues to occur, then the whole chromosome with the lost from the cell after multiple rounds of replication and the cell would die. It will also result in the deletion of important genes from the chromosomes. So this problem is solved by enzyme telomerase.

Telomerase enzyme provides an RNA template for the addition of repetitive DNA sequences at the tips of the chromosome and these sequences are called as telomeres.

Because the enzyme is using RNA template for the formation of DNA, it is also called as RNA dependent DNA polymerase. Another example of this type of enzyme is reverse transcriptase which is found in retroviruses. This process is called as reverse transcription, the formation of DNA from RNA.

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