Question

What is the reason for the difference in the synthesis of the leading and lagging strands of DNA molecules? Choose one below

A.) One strand must be completely synthesized before synthesis of the next can begin.

B.) Helicase and SSB proteins work only at the 5' end of the chromosome.

C.) The origins of replication occur only at the 5' end of the chromosome.

D.) DNA polymerase can join new nucleotides only to the 3' end of the growing strand.

E.) DNA ligase only works in the 3' to 5' direction

Answer 1

(D) DNA polymerase can join nucleotides only to the 3' end of growing strand.

Elongation of the growing nucleotide chain occurs by the action of DNA polymerase. α phosphoryl group of incoming nucleoside triphosphatase is attacked by OH group of 3' end which result in release of pyrophosphate (βand γ phosphates of nucleoside) and formation of phosphodiester bond between the nucleotides.

Other options are incorrect because:

Both the leading and lagging strand synthesis occurs simultaneously, leading strand undergoes continuos replication and lagging strand synthesis occurs by okazaki fragments.

Helicase and SSB proteins are required for unwinding of DNA for loading of replication machinery. Helicase unzip DNA in 5'--> 3' direction and SSB's bind to open DNA irrespective of the direction.

Origin Of replication is a DNA sequence at which replication is initiated, there is no specific 5' or 3' location on chromosome at which origin of replication occurs, rather presence of specific sequences make origin of replication unique.

DNA ligase are catalyze the formation of covalent bond between 3'OH and 5' phosphate by using energy from ATP synthesis.