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biology

The Okazaki fragments in DNA chain growth

A

Results in transcription

B

Polymerise in the 3' to 5' direction and forms replication fork

C

Proves semi-conservative nature of DNA replication

D

Polymerise in the 5' to 3' direction and explain 3' to 5' DNA replication

Answer

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.

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toppr

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