Question

Okazaki fragments during DNA replication:
A. Polymerise in \[5'\to 3'\] direction and explain \[3'\to 5'\] DNA replication
B. Prove semiconservative DNA replication
C. Polymerise in \[3'\to 5'\] direction and replication fork
D. Cause transcription

Answer 1

Hint: Leading or continuous strands are those strands on which replication is continuous and grows in the direction of the replication fork. The lagging strand is called the discontinuous strand on which replication is in the opposite direction of the replication fork.

Step by step solution:
DNA replication always takes place in the \[5'\to3'\] direction. The strands which are synthesized discontinuously are called Okazaki fragments and always replicate in \[5'\to3'\] direction and explain in \[3'\to5'\] direction. To replicate the lagging strand in the \[5'\to3'\] direction, the template strand must occur in opposite direction. To do so, primers are added after every few hundred bases. These primers run in \[5'to3\] direction and form Okazaki fragments and are later joined together by DNA ligase. So option A is correct.

The semiconservative nature of DNA is shown by both strands. Each of the DNA strands acts as a template for the synthesis of a new strand and forms two DNA molecules. The new DNA molecules contain one parental strand and one newly synthesized strand. So option B is incorrect.

Okazaki fragments replicate in \[5'\to3'\] direction and in the opposite direction of the replication fork. So option C is incorrect.

Transcription is the process by which RNA is formed by DNA using RNA polymerase and for this, any of the DNA strands can be taken as a template strand. So option D is incorrect.

So, option A is correct.

Note: The DNA unwinds with the help of enzyme helicase and forms a replication fork. Primer is used to start the process of replication. As the enzyme can only synthesise the new strand in \[5'\to3'\] direction, the replication of the leading strand is continuous while the replication on the lagging strand primer is added after every few hundred bases and is later joined by DNA ligase.