Question

DNA synthesis can NOT be initiated by the _________.

a Terminal protein providing the first dCTP nucleotide
b DNA primer at the 5'-OH
c RNA primer with a 3'-OH
d DNA primer at the 3'-OH

Answer 1

DNA synthesis cannot be initiated by the DNA primer at the 5'-OH. The correct option is b.

Step-by-step explanation:

DNA synthesis cannot begin with a DNA primer at the 5'-OH because DNA polymerases need a free 3'-OH group to initiate nucleotide addition. This is because DNA polymerases require a free 3'-OH group to start the addition of nucleotides. Thus, the correct primer needed for DNA synthesis must have a free 3'-OH end, which is typically provided by an RNA primer synthesized by primase.

This RNA primer allows DNA polymerase to start adding nucleotides, forming a new DNA strand. A DNA primer at the 5'-OH does not provide the necessary free 3'-OH group for DNA polymerase to work. Hence, b is the correct option.