ID #1823

Why proofreading occurs in 3'-5' direction?

In proofreading, DNA Pol I reads from the 3'-5' direction so that if it finds a base that is not "correct", it can pluck it out and replace the base in the 5'-3' direction, seeing that synthesis only occurs in the 5'-3' direction.
One has to remove from the 3' end, because that's the base you just added. And you have to be doing synthesis in the 5'-3' direction. It makes sense to you because it's the only way it can work!

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