Which of the following is not correct with reference to DNA replication?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → The DNA polymerases on their own can initiate the process of replication.
DNA replication is carried out mainly by DNA-dependent DNA polymerase, but this enzyme cannot start the process by itself. Replication also does not begin at random: it starts at a definite region called the origin of replication, and it proceeds at a small opening of the helix called the replication fork.
Option (1) The DNA polymerases on their own can initiate the process of replication. — An incorrect statement. The DNA polymerases on their own cannot initiate replication. The word can makes this statement wrong, so it is the answer.
Option (2) There is a definite region in E. coli DNA where the replication originates. — A correct statement. The definite region in E. coli DNA where replication starts is the origin of replication; this is why a vector must provide an origin of replication in recombinant DNA work.
Option (3) In eukaryotes, the replication of DNA takes place at S-phase of the cell-cycle. — A correct statement. In eukaryotes DNA is replicated in the S-phase of the cell cycle, and replication must be coordinated with cell division.
Option (4) The replication occurs within a small opening of the DNA helix, referred to as replication fork. — A correct statement. The two strands cannot be separated along the whole length because of the very high energy needed, so replication takes place within a small opening, the replication fork.
NCERT Extract:
The Machinery and the Enzymes – “… The DNA polymerases on their own cannot initiate the process of replication. Also the replication does not initiate randomly at any place in DNA. There is a definite region in E. coli DNA where the replication originates. Such regions are termed as origin of replication.”
The Machinery and the Enzymes – “… In eukaryotes, the replication of DNA takes place at S-phase of the cell-cycle. The replication of DNA and cell division cycle should be highly coordinated.”