Question

Define and indicate the significance of (a) Okazaki fragments, (b) DNA ligase, and (c) primer RNA during DNA replication.

Short answer

Question: Explain the role and significance of Okazaki fragments, DNA ligase, and primer RNA during DNA replication. Answer: Okazaki fragments are short sequences of DNA nucleotides formed on the lagging strand during DNA replication, allowing replication to proceed in the opposite direction of the DNA replication fork. DNA ligase is an enzyme that joins the Okazaki fragments together, ensuring the fidelity of the replication process. Primer RNA are short RNA molecules that serve as starting points for DNA synthesis as DNA polymerase requires a free 3' hydroxyl group to begin. These components are essential in maintaining an accurate and complete replication process.

Step-by-step solution

(a) Okazaki Fragments)

Okazaki fragments are short sequences of DNA nucleotides, approximately 100-200 base pairs long in eukaryotic cells and about 1000-2000 base pairs in prokaryotic cells. They are formed on the lagging strand during DNA replication. The significance of Okazaki fragments is that their formation allows replication to proceed in the opposite direction of the DNA replication fork, as DNA polymerase can only synthesize new DNA in the 5' to 3' direction. Okazaki fragments are subsequently joined together by DNA ligase to form a continuous lagging strand.

(b) DNA Ligase)

DNA ligase is an enzyme that has a crucial role in the process of DNA replication. It catalyzes the formation of phosphodiester bonds between the Okazaki fragments on the lagging strand. This forms a continuous DNA strand, ensuring that the newly synthesized DNA strand is complete and accurate. The significance of DNA ligase is that it ensures the fidelity of the replication process, preventing errors that could potentially harm the organism or cause genetic mutations.

(c) Primer RNA)

Primer RNA, or RNA primers, are short, single-stranded RNA molecules that are complementary to the DNA template strand. They serve as starting points for DNA synthesis during replication. The primer is synthesized by an enzyme called primase, which forms short RNA sequences complementary to the DNA strand. DNA polymerase III can then attach nucleotides to the 3’ end of the RNA primer, extending the newly synthesized DNA strand. The significance of primer RNA is that DNA polymerase requires a free 3' hydroxyl group to begin DNA synthesis and cannot initiate synthesis directly without it. The RNA primer provides this necessary starting point, allowing DNA replication to proceed.