Question

1.      Describe the details of these two fundamental properties of the activity of DNA polymerase

         a. The direction of synthesis of the chain growth of the new strand

            

         

            b.  What is required for DNA polymerase to add additional nucleotides?

Answer 1

A. DNA polymerase is responsible for the polymerization of daughter DNA molecules during the process of DNA replication. It uses parental DNA strand as DNA template. The parental DNA strand and the daughter DNA molecule are complementary to each other. The direction of polymerization of DNA by DNA polymerase is 5' to 3', that is, the daughter DNA is synthesized in this direction.

This enzyme moves continuously in this direction on the leading strand. Only one long molecule of daughter DNA is synthesized on this strand. But the direction on the opposite parental strand is not 5' to 3'. It has to move in 3' to 5' direction. Therefore to solve this problem, this enzyme synthesizes DNA discontinuously on this strand. This strand is said to be the lagging strand. Many small fragments of DNA are synthesized using lagging strand as a template. This fragments are called as okazaki fragments. When the process of DNA replication is completed, all the okazaki fragments are joined together by DNA ligase enzyme.

B. DNA polymerase alone cannot initiate the process of DNA polymerization. It is because it cannot add deoxyribonucleotides directly. It required a free hydroxyl group to which it can add dNTPs. This free hydroxyl group is provided by RNA primer which is synthesized by enzyme called as primase. Once primer is synthesized, DNA polymerase start its activity of adding deoxyribonucleotides. When the process of replication is completed, primers are removed by DNA polymerase 1 enzyme.

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