Question

Use 3-4 sentences to explain Why you have a leading and lagging strand. (dont explain about replicatoin, I need a reason why we need leading and lagging strand)!

Use you own words!!

Answer 1

When DNA replication happens the continous complimentary strand sythesized from 3^I end of the template strand by enzyme DNA polymerase enzyme is called as leading starnd. DNA polymerase can add nucleotides only in one direction of the replication fork. Whereas to synthesize complimentary strand from opposite direction enzyme primase is responsible .It synthesizes DNA strands from the direction opposite to that of the replication fork. Hence they are synthesized discontinously in smaller bits of fragments which are referred to as lagging strand and are ligated to form a continous strand.

Hence when leading starnd is synthesized continously towards the direction of the moving replication fork due to continous unwinding of the DNA whereas lagging starnd cannot be synthesized continously since the replication happens in the direction opposite to the replication fork. So they are formed in small dicontinous bits as and when a small stretch of double staranded DNA is unwound.

Answer 2

On the leading strand DNA replication proceeds continuously along the DNA molecule as the parent double-stranded DNA is unwound, but on the lagging strand the new DNA is made in installments, which are later joined together by aDNA ligase enzyme. This is because the enzymes that synthesise the new DNA can only work in one direction along the parent DNA molecule. On the leading strand this route is continuous, but on the lagging strand it is discontinuous.