Year 12s: what will be the first way you research your future options? >>

Transcription/Translation Question

Hey guys, so we have been doing protein synthesis in A2 Biology and I have a question.

So obviously mRNA is made using a copy of -one- strand (the antisense strand) of DNA. This then codes for a specific protein to be made in translation.

My question is, how does the RNA Polymerase know which strand of the gene/DNA to use as the template? Surely it will create a different strand of mRNA - and therefore a different protein - if it uses the other strand?

Is it possibly because only the one strand of the DNA will have the "Start" codon?

Thanks in advance for any replies.

Posted from TSR Mobile

(edited 10 years ago)

Reply 1

Rob da Mop

Almost. The start codon tells the ribosome where to start translating, not the RNA polymerase to start transcribing.

The RNA polymerase machinery needs to bind to certain motifs upstream of the section to be transcribed which determines which strand is used and where transcription starts. It's similar in concept to the start codon but also ties in with a lot of the complicated controls on which genes are transcribed when, in which cells etc. which makes it a lot more complicated.

Reply 2

Ashnard

In addition to what Rob da Mop said, remember that the RNA polymerase can only synthesise RNA in one direction (5' -> 3'). So once the RNA polymerase binds to the upstream promoter and melts the DNA, it can only possibly synthesise RNA from one of the strands, but not the other anti-parallel strand.