Which of the following is true regarding Okazaki fragment?
**Core Concept**
Okazaki fragments are short, discontinuous segments of DNA that are synthesized on the lagging strand during DNA replication. They are formed due to the antiparallel nature of DNA, where the leading strand is synthesized continuously, whereas the lagging strand is synthesized in short, discontinuous segments.
**Why the Correct Answer is Right**
Okazaki fragments are indeed necessary for the synthesis of the lagging strand. As the replication fork moves, the lagging strand is synthesized in short, discontinuous segments because the DNA polymerase can only synthesize DNA in one direction. These segments, or Okazaki fragments, are typically 1000-2000 nucleotides long and are joined together by DNA ligase after replication is complete. The sequential synthesis of Okazaki fragments is essential for the accurate replication of the lagging strand.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because Okazaki fragments are segments of DNA attached to an RNA primer, not RNA itself. The RNA primer is later removed by RNase H and replaced with DNA.
**Option B:** Incorrect because Okazaki fragments are related to the lagging strand, not the leading strand. The leading strand is synthesized continuously, whereas the lagging strand is synthesized in short, discontinuous segments.
**Option D:** Incorrect because helicase actually acts on both strands of DNA to unwind the double helix, but it does not specifically target the leading strand. The action of helicase is essential for the unwinding of DNA, allowing the replication machinery to access the template strands.
**Clinical Pearl / High-Yield Fact**
A key aspect of Okazaki fragment synthesis is the role of RNA primers, which are essential for initiating DNA synthesis. The RNA primers are later removed and replaced with DNA, ensuring that the final product is a continuous strand of DNA. This process is critical for accurate DNA replication and repair.
**✓ Correct Answer: C. Several Okazaki fragments must be sequentially synthesized for each replication fork**