Question

The end replication problem arises because:

a) DNA polymerase can only add nucleotides in one direction

b) helicases cannot unwind the end of chromosomes because they are not AT rich sequences but TG rich

c) The replisome holoenzyme isn’t properly recruited to the end of chromosomes

d) Primers are made of RNA

e) DNA polymerase needs a clamp to synthetize DNA until the end of chromosome and without this it falls off the end

Answer 1

Answer a. a) DNA polymerase can only add nucleotides in one direction.

Explanation- DNA polymerase requires RNA primer for intiation of DNA synthesis. DNA polymerase can add nucleotide only in 5' to 3'.

Leading strand is completely synthesised from end to end, however lagging strand requires new RNA primer as the DNA unwinds. At the end of DNA synthesis of lagging strand, DNA cannot be synthesized as RNA primer cannot be attached to DNA for initiation of DNA synthesis.