Question

DNA synthesis can NOT be initiated by the _________.

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

Answer 1

DNA synthesis cannot be initiated by a DNA primer at the 5'-OH end because DNA polymerase requires a free 3'-OH group provided by an RNA primer to start the addition of nucleotides in the 5' to 3' direction.

Step-by-step explanation:

DNA synthesis cannot be initiated by the DNA primer at the 5'-OH. During DNA replication, DNA polymerase can only add nucleotides in the 5' to 3' direction, and it also requires a free 3'-OH group to initiate this process.

The primer needed for DNA polymerase to begin synthesis is usually an RNA primer synthesized by primase, which provides this crucial free 3'-OH group on its 3' end. DNA polymerases cannot add nucleotides to a free 5'-OH group because that would be the opposite direction of synthesis (3' to 5'), which they are not capable of doing.

The RNA primer allows the DNA polymerase to add the first DNA nucleotide to the RNA's 3'-OH end, and from there, it continues adding nucleotides to elongate the new DNA strand.