Question

Which of the following is explained by the Reiji Okazaki experimentation?

• A. Continuous synthesis of DNA.
• B. Semiconservative mode of replication.
• C. Dispersive mode of replication.
• D. Semidiscontinuous synthesis of DNA.

Hint:

Summary of DNA replication models:
- Meselson-Stahl experiment proved Semiconservative replication.
- Okazaki experiments proved Semidiscontinuous replication (Leading/Lagging strands).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
DNA replication is highly coordinated, but the antiparallel nature of the DNA double helix presents a major challenge:
DNA polymerases can only synthesize DNA in the 5' to 3' direction.
Because the replication fork moves in one direction, only one template strand can be copied continuously.

Step 2: Detailed Explanation:
In 1968, Reiji Okazaki and his colleagues performed pulse-labeling experiments using radioactive thymidine in replicating E. coli cells.
They discovered that a significant portion of the newly synthesized DNA existed as short fragments (approximately \(1000-2000\) nucleotides long), which they called Okazaki fragments.
Over time, these short fragments were joined together by DNA ligase to form a long, continuous DNA strand.
This experiment proved that DNA replication is semidiscontinuous:
- The leading strand is synthesized continuously in the 5' to 3' direction, moving toward the replication fork.
- The lagging strand is synthesized discontinuously as short Okazaki fragments in the 5' to 3' direction, moving away from the replication fork.
This model resolved the paradox of how antiparallel DNA is replicated simultaneously by 5'-to-3' polymerases.

Step 3: Final Answer:
Reiji Okazaki's experimentation explained the semidiscontinuous synthesis of DNA.