Question

Given below are two statements:
Statement (I): DNA replication proceeds in a bidirectional manner from multiple origins of replication in prokaryotic cells.
Statement (II): Okazaki fragments are short DNA fragments synthesized on the leading strand during DNA replication in both prokaryotic and eukaryotic cells.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

To avoid confusion:
- Prokaryotes: Single origin (oriC), circular DNA.
- Eukaryotes: Multiple origins, linear DNA.
- Leading strand: Continuous synthesis.
- Lagging strand: Discontinuous synthesis via Okazaki fragments.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule.
It follows different spatial and initiation patterns in prokaryotes compared to eukaryotes due to differences in chromosome structure.

Step 2: Detailed Explanation:
Let us analyze the correctness of each statement:
- Statement (I): Prokaryotes typically have a single circular chromosome with a single origin of replication (referred to as oriC in E. coli).
Replication initiates at this single site and proceeds bidirectionally around the circular chromosome until the two replication forks meet at the termination site.
Eukaryotic chromosomes, being much larger and linear, utilize multiple origins of replication to complete replication within a reasonable timeframe.
Therefore, Statement (I) is false because prokaryotes have a single origin, not multiple origins.
- Statement (II): DNA polymerase can only synthesize DNA in the \(5'\) to \(3'\) direction.
Because the two template strands are antiparallel:
1. The leading strand template allows for continuous DNA synthesis in the direction of the replication fork movement.
2. The lagging strand template requires discontinuous DNA synthesis in the direction away from the replication fork.
This results in the synthesis of short, discontinuous segments of DNA called Okazaki fragments, which are eventually joined together by DNA ligase.
Therefore, Okazaki fragments are synthesized on the lagging strand, not the leading strand, making Statement (II) false.
Since both statements are false, Option (B) is correct.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are false.