Question

RNA primers in Okazaki fragments are usually very short, less than 10 nucleotides and sometimes as short at 2 nucleotides in length. What does this fact tell you about theprocessivityof the primase enzyme—that is, the relative ability of the enzyme to continue polymerization as opposed to dissociating from the template and from the molecule being synthesized? Which enzyme is likely to have a greater processivity, primase or DNA polymerase III?

Answer 1

Answer:

During DNA replication each parental DNA strand serves as a template to a new complementary strand. DNA polymerase is the main enzyme responsible for this process, it catalyzes the addition of nucleotides to form the new DNA chain.  

The complementary nature of the DNA strands, presents a difficulty for DNA replication: DNA polymerase catalyzes the polymerization of DNA only in the 5’ to3’ -in the leading DNA strand. Thus, the opposite DNA strand, the lagging strand, faced an obstacle that is solved by the Okazaki small fragments. The primase enzyme synthesizes small RNA fragments complementary to the lagging DNA strand. These RNA fragments serve as primers for the DNA polymerase. To remove this RNA primers and form a continuous complementary lagging strand, RNase H and DNAse ligase will further cut and join the DNA again.  

DNA polymerase has a higher processivity than primase, if processivity is the average number of nucleotides that it is capable to continuously add to the template strand. Primase dissociates from the template often during DNA replication as it has to constantly add new RNA primers to the strand.