DNA polymerase DNA ligase

What's the difference?

In semi conservative replication - what does DNA polymerase do? As nucleotides join up to their complementary bases naturally due to attractions, why does DNA polymerase need to be there?

I'm so confused because in Polyermase Chain Reaction, DNA polymerase is used to join together nucleotides and form a sugar phosphate backbone. But I thought DNA ligase does that?!

No chance you're doing Higher Biology is there? Just wondering
But I'm pretty sure DNA polymerase unwinds the DNA double helix and adds on nucleotides to the primer(s) on the leading and lagging strands while forming the sugar-phosphate backbone. Oh, and it is taq DNA polymerase that does it in PCR because it has to be heat tolerant
But your DNA ligase description was only the tiniest bit off. DNA ligase joins together the fragments of DNA on the lagging strand and, if it is relevant to you, it also joins together the complementary sticks ends of the DNA transferred into the plasmid in recombinant DNA technology. Hope that helps!


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DNA polymerase doesn't unwind, helicase does, but other than that, yes.

OP, to answer the question of why DNA polymerase needs to be there, I would guess that seeing as it is an enzyme, although the process may happen naturally the enzyme likely catalyses it? DNA polymerase is needed therefore to efficiently bind the free
nucleotides and initiate replication.


Also, I think you may be confusing the sugar phosphate backbone with a sugar-phosphate bond (phosphodiester). The sugar-phosphate bond forms the structure of DNA strands and it is contains sugar-phosphate bonds which join the nucleotides. DNA ligase forms sugar-phosphate bonds between the fragments of DNA on the lagging strand (i.e. sealing the "nicks" or gaps).
DNA polymerase does indeed form a sugar phosphate backbone by joining nucleotides.

Hope that helps

But to form the sugar phosphate backbone in the first place you need to form phosphodiester bonds? Yes When I said that DNA polymerase forms a sugar phosphate backbone, doesn't that basically mean it joins together phosphates and pentose sugars on nucleotides? Yes

My question is, why isn't DNA ligase present in PCR, when DNA ligase joins the backbone together in the new DNA strand. Only between nicks.
How does it do it without it?

Replication on the lagging strand is discontinuous as DNA polymerase initiates replication at many different points along the lagging strand, provided that there is a primer present. This results in many short fragments.

Once the primer is removed, it is replaced with DNA. This still leaves a gap between the fragments. The role of DNA ligase is only to seal these gaps with a sugar-phosphate bond so the strand becomes a continuous one.

The sugar-phosphate bonds of the fragments themselves are still made by DNA polymerase adding free nucleotides.

Here's an answer to why DNA ligase is not needed (googled, as I did not know this myself):
"PCR is only used on short DNA sequences, and it's done in a controlled environment (a test tube), so it only requires the bare minimum to work. Ligase isn't needed because there should never be any nicks that need to be sealed or cut ends that need to be bound."

I hope this is now clearer