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What are the fundamental reasons why DNA replication on the lagging strand cannot be polymerized in 3' to 5' direction?
Question Date: 2021-09-22
Answer 1:

I'm not a geneticist, but I suspect that it's a combination of the molecular shape of the DNA bases and the binding site shape of the enzymes responsible for replication.

As you know, the 5' and 3' ends are not the same shape.

When bases are oriented the "wrong" way, it may not bind to the DNA polymerase.

Answer 2:

The DNA polymerases don't move in that direction. It's vaguely analogous to you having to do half your walking backwards - it wouldn't work well. Lots of things only move in 1 direction - water flows downhill. Escalators move in only 1 direction. Hot air rises.

Here's a link:
DNA polymerase adds nucleotides to the deoxyribose (3') ended strand in a 5' to 3' direction. Nucleotides cannot be added to the phosphate (5') end because DNA polymerase can only add DNA nucleotides in a 5' to 3' direction. The lagging strand is therefore synthesized in fragments.


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