Question

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

Short answer

Answer: In DNA replication, Okazaki fragments are short sequences of DNA formed on the lagging strand, allowing proper replication of the entire genetic information. DNA ligase joins these fragments together by forming phosphodiester bonds to create a continuous DNA strand. Primer RNA is a short segment that serves as a starting point for DNA synthesis, enabling DNA polymerase to initiate replication and accurately replicate the genetic information within the DNA molecule.

Step-by-step solution

(a) Okazaki Fragments

Okazaki fragments are short sequences of DNA, typically around 100-200 nucleotides long in eukaryotes and 1000-2000 nucleotides long in prokaryotes. They are a result of the lagging strand synthesis during DNA replication. Since DNA replication occurs in the 5' to 3' direction, the lagging strand is synthesized in a discontinuous manner through the formation of these short fragments. Later, these fragments are joined together to form a continuous strand. The significance of Okazaki fragments is that they enable the proper replication of DNA on the lagging strand, ensuring that the entirety of the genetic information is preserved in the newly synthesized DNA molecule.

(b) DNA Ligase

DNA ligase is an essential enzyme in the DNA replication process. Its primary role is to join together the Okazaki fragments that are synthesized on the lagging strand. DNA ligase accomplishes this by forming phosphodiester bonds between the adjacent fragments, thereby creating a continuous DNA strand. This process is crucial for maintaining the integrity and continuity of the genetic information, as it ensures the accurate replication of the entire DNA molecule.

(c) Primer RNA

Primer RNA is a short segment of RNA that serves as a starting point for DNA synthesis during the DNA replication process. DNA polymerase, the enzyme responsible for synthesizing new DNA strands, cannot initiate synthesis on its own; it requires a primer to provide a free 3' hydroxyl group to which it can add new nucleotides. Primer RNA is synthesized by an enzyme called primase, which creates a short RNA sequence complementary to the DNA strand being replicated. Once the primer is in place, DNA polymerase can begin to extend the new DNA strand. The significance of primer RNA during DNA replication is that it provides the necessary starting point for DNA synthesis, allowing for the accurate replication of the genetic information within the DNA molecule.