Question

During DNA replication, the addition of nucleotides on the lagging strand occurs
(a) Towards the replication fork
(b) At a faster rate than the leading strand
(c) Continuously
(d) Discontinuously

Answer 1

In the duplex DNA molecule, both the strands are arranged antiparallel to one another. The enzyme catalyzing the reaction of DNA synthesis can add nucleotides in only one direction. This results in the creation of two types of strands.

Complete answer:
DNA replication is the first step of reproduction where new DNA strands are produced to transfer the information or characters from parents to offspring. In DNA replication, polymerization reaction occurs in the 5’ to 3’ direction wherein, new nucleotides are added at the 3’-OH end of a growing polynucleotide chain. DNA polymerase can catalyze polymerization in 5’ to 3’ direction and hence continuous polymerization occurs on 3’ to 5’ strand i.e. it is the leading strand while the replication of 5’ to 3’ strand of the DNA molecule is discontinuous and is known as lagging strand. Short segments of DNA are synthesized called Okazaki fragments which are joined later with the help of DNA ligases.

Additional Information: -The specific regions in the genome of an organism where replication begins are called ‘origin’. The process involves the action of many different enzymes the first of which is helicase. It helps in the unwinding of the double-stranded DNA molecule.
-There exist certain proteins called Single-strand binding proteins (SSB) that stabilize the unwound DNA strands. Another enzyme named as Topoisomerase helps in reducing the stress that occurs in the molecule as a result of unwinding. This entire assembly, with unwound DNA that looks like an inverted Y shape, is called the Replication fork.
-Primase synthesizes a short stretch of RNA primer on the DNA template. It provides a free 3’-OH for the DNA polymerase to initiate the DNA replication.
-DNA replication follows a semi-conservative and semi-discontinuous approach that occurs always in the 5'-3’ direction.
So, the correct answer is ‘Discontinuously.’

Note: -In semi-conservative DNA replication, each of the separated strands is used as a template to synthesize a new daughter DNA strand. Thus, a new daughter DNA molecule contains both the parent strand and a newly synthesized DNA strand. It was suggested by Meselson and Stahl.
-DNA replication takes place during the S-phase of interphase in the cell cycle.