Question

The Okazaki fragments in DNA chain growth

• A. Polymerise in the 3' to 5' direction and forms replication fork
• B. Results in transcription
• C. Proves semi-conservative nature of DNA replication
• D. Polymerise in the 5' to 3' direction and explain 3' to 5' DNA replication

Answer 1

Answer: (D)

As we know that the two strands of the parental DNA duplex are antiparallel, and DNA synthesis always occurs in the 5'-->3' direction, not in 3’--> 5’ direction, because chain growth results from formation of a phosphodiester bond between the 3' oxygen of a growing strand and alpha phosphate of a dNTP. This makes option B incorrect.

To facilitate the growth of the lagging strand in the 5'-->3' direction, copying of its template strand must somehow occur in the opposite direction from the movement of the replication fork (3' -->5’). This is done by synthesizing a new primer every few hundred bases on the second parental strand. Each of these primers is elongated in the 5'-->3' direction and form discontinuous segments called Okazaki fragments which are later joined together by DNA ligase. This makes option D correct.