The replication fork consists of four components. Which of the following components is responsible for synthesis of the short RNA molecules essential for DNA replication?
A. HelicaseB. Primase
C. Polymerase
D. SSB
Answer. B. Primase
Primase synthesizes the short RNA molecules
required for initiation of a new DNA strand.
DNA synthesis requires an
RNA primer because polymerase, the major enzyme for DNA replication, can only add bases to an existing strand and
cannot begin a new strand de novo. DNA polymerase moves along
the DNA in
one
direction and synthesizes
both new DNA strands at
once. Since DNA is always synthesized 5' to 3', one of the strands (the leading strand) is synthesized
continuously,
whereas the other (the lagging strand) is synthesized in short stretches called
Okazaki fragments. Helicase is the enzyme responsible for unwinding DNA at the replication fork. SSBs (single-strand
binding proteins) bind to the unwound DNA to prevent pre mature
re-annealing.
