Which way is DNA read?
First, DNA polymerase builds a new strand of DNA in the 5′ to 3′ direction. Always. The new strand is built 5′ –> 3′.
Second, when people look at DNA sequences, the convention is to read it in 5″ –> 3′
With that in mind…
DNA polymerase = only synthesizes DNA in the 5′ to 3′ direction.
Because DNA polymerase goes in the 5′ –> 3′, it has to start on the 3′ end of the old strand.
Here’s a recap of the steps…
- — When DNA is replicated, the two complementary strands part. One strand runs 5′ –> 3′. One strand runs 3′ –> 5′
- — DNA polymerase comes in to replicate the new strands. It does this by complementary base pairing which each of the two strands
- — DNA polymerase can only synthesize in the 5′ –> 3′ direction. That’s the new strand. It will start at the 3′ end of the original template strand.
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