Question

Why is an RNA primer considered essential for DNA synthesis by DNA polymerase III?

a. there is no particular reason; that is simply what has been observed
b. the enzyme requires a free 3'-OH group
c. the enzyme requires a free 3'-PO4 group
d. the enzyme requires a free 5'-PO4 group

Answer 1

An RNA primer is essential for DNA synthesis by DNA polymerase III because it provides the necessary free 3'-OH group that the enzyme requires to start DNA synthesis.

Step-by-step explanation:

An RNA primer is considered essential for DNA synthesis by DNA polymerase III because the enzyme requires a free 3'-OH group to initiate synthesis. DNA polymerase III cannot start DNA synthesis from scratch and needs to add new nucleotides to the free 3' hydroxyl group of a pre-existing strand. The RNA primer is a short complementary sequence of five to 10 RNA nucleotides synthesized by the enzyme primase, which is part of a primosome complex and provides the necessary free 3'-OH group to which DNA polymerase can add DNA nucleotides.