Question

The Okazaki fragments in DNA chain growth
A. Result in transcription.
B. Polymerize in the \[3' \to 5'\] direction and form a replication fork.
C. Prove semi-conservative nature of DNA replication.
D. Polymerize in the \[5' \to 3'\] direction and explain \[3' \to 5'\] DNA replication.

Answer 1

Hint: In DNA replication, the problem arises as the DNA strands run antiparallel to each other and DNA polymerase acts only in one direction. So this problem is solved by \[150\] to \[200\] base pairs of long DNA fragments that are synthesized discontinuously and afterwards linked together by the enzyme DNA ligase called as Okazaki Fragments.

Complete answer: In the process of DNA synthesis, there are two strands in the replication fork. One of the strands runs \[5' \to 3'\] orientation moving towards the fork. This strand is called a lagging strand and it undergoes discontinuous DNA synthesis. The strand which supports the continuous DNA synthesis is called a leading strand.
 -DNA polymerase moves always from the replication fork on this lagging strand while on this leading strand DNA polymerase moves towards the replication fork.
-DNA polymerase always adds base nucleotides to the \[3'\] end of a primer. DNA replication is continuous on the leading strand and discontinuous on the lagging strand. DNA polymerase cannot initiate replication; it can only add new nucleotides to an existing strand. For DNA replication to occur, an RNA primer must first be synthesised to provide an attachment point for DNA polymerase.
-In replication, DNA polymerase always attaches new nucleotides to the 3’ end of a primer, extending the new chain in a \[5' \to 3'\] direction.
-Okazaki fragments in DNA are sealed by the enzyme DNA ligase. Replication of DNA strand always occurs in 5′ – 3′ direction. Okazaki fragments synthesised on \[3' \to 5'\] DNA template, attach to form lagging strands which grow in \[3' \to 5'\] direction.
Hence, the correct option is (D) Polymerize in the \[5' \to 3'\] direction and explains \[3' \to 5'\] DNA replication.

Note: The Okazaki fragments are necessary for DNA synthesis because there is no \[3' \to 5'\] strand of DNA for the DNA polymerase to use it as a continuous template.
Therefore, the Okazaki fragments allows for discontinuous DNA synthesis by allowing the DNA polymerase to work backwards, moving away from the replication fork, but then jumping back to the next RNA primer to start a new Okazaki fragment.