PCR verses semi conservative replication

This is for ocr biology spec, but i’m confused on why a primer is needed for PCR but not necessary for semi conservative replication. Is it because the primer will attach to a 5’ end as it attaches to both the strands in PCR but in semi conservative replication it only attaches to the 3’ end. I forget why DNA polymerase can only synthesise from the 3’ end.

Reply 1

Gabi26

I do AQA, but as far as I remember for PCR, primers bind to both strands of the DNA at either end, it signals for DNA polymerase where to bind and begin synthesising a complementary strand, but it also prevents the DNA strand from joining up/sticking to itself.
Though from what I read online it does say that semi-conservative replication does require a primer to be added, I just don't think it's included in the specs (at least not in the AQA one, I'm not really sure for OCR), the process of DNA replication is far more complicated that what A level teaches.
Also DNA is synthesised from the 5' end.

I'm not sure how helpful this can be, but I'm also interested in other people's responses.

This is where I looked online btw: https://www.ncbi.nlm.nih.gov/books/NBK9940/

Reply 2