Why do Okazaki fragments form? Choose the best answer: a.Because the machinery responsible for replicating the lagging strand only works in small portions at a time so that we observe one long strand of DNA on the leading strand and lots of short fragments on the lagging strand. b.Because replication only proceeds in ohe direction and the lagging strand is only expose a little at a time so that primase binds intermittently and polymerases replicate short pieces of DNA known as fragments. c.Because the tension created by unwinding the DNA causes the polymerases to not bind stably to the lagging strand so they fall off frequently causing the formation of small fragements of replicated DNA. d.Because the ligase prioritizes tying up loose ends on the leading strand so that we observe lots of unligated fragments of DNA on the lagging strand.
The Correct Answer and Explanation is :
The best answer is b. Because replication only proceeds in one direction, and the lagging strand is only exposed a little at a time so that primase binds intermittently and polymerases replicate short pieces of DNA known as fragments.
Explanation
DNA replication is a vital biological process that ensures accurate duplication of genetic material during cell division. This process occurs in the context of the double-stranded DNA helix unwinding, which presents distinct challenges for synthesizing the two strands: the leading strand and the lagging strand.
Replication of DNA occurs in a 5′ to 3′ direction, which means that the machinery that synthesizes DNA can only add nucleotides to the 3′ end of a growing strand. The leading strand can be synthesized continuously as the replication fork opens up, allowing DNA polymerase to work smoothly along it. However, the lagging strand presents a unique problem because it runs in the opposite direction of the replication fork’s movement.
As the replication fork unwinds the DNA, only a short segment of the lagging strand is exposed at any given time. Consequently, the enzyme primase synthesizes short RNA primers at various intervals along the lagging strand to provide a starting point for DNA polymerase. This results in the synthesis of short segments of DNA, known as Okazaki fragments. Each fragment is initiated by a primer, and DNA polymerase extends these fragments until it reaches the next primer.
After the synthesis of these fragments, another enzyme, DNA ligase, joins these segments together to create a continuous strand. Thus, Okazaki fragments are an essential feature of DNA replication on the lagging strand, resulting from the need for intermittent priming and the unidirectional nature of DNA polymerization. This mechanism is crucial for ensuring that the entire DNA molecule is accurately replicated before cell division, maintaining genetic fidelity.