Question

Which of the following statements in NOT true about DNA replication? DNA replication involves synthesis of multiple RNA primers DNA ligase is needed for successful DNA replication DNA replication requires deoxyribonucleotide triphosphates High fidelity of DNA replication is ensured by 5-3' exonuclease activity of DNA polymerase High fidelity of DNA replication is ensured by 3-5' exonuclease activity of DNA polymerases Next

Answer 1

A) RNA primers are used by living organisms in the initiation of synthesizing a strand of DNA. Unlike in the leading strand, this method results in the repeated starting and stopping of DNA synthesis, requiring multiple RNA primers.

B) DNA ligase is an enzyme that repairs irregularities or breaks in the backbone of double-stranded DNA molecules. It has important role in the process of DNA replication and DNA repair. DNA ligase functions by forming a bond between the end of a “donor” nucleotide and the end of an “acceptor” nucleotide.

C) In prokaryotes, DNA polymerase I synthesizes the Okazaki fragment until it reaches the previous RNA primer. Then the enzyme simultaneously acts as a 5′→3′ exonuclease, removing primer ribonucleotides in front and adding deoxyribonucleotides behind until the region has been replaced by DNA, leaving a small gap in the DNA backbone between Okazaki fragments which is sealed by DNA ligase.

D) DNA runs in the 5′→3′ direction. Since DNA polymerase cannot add bases in the 3′→5′ direction complementary to the template strand, DNA is synthesized ‘backward’ in short fragments moving away from the replication fork, known as Okazaki fragments.

Therefore, last option is NOT true.