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Triplet code - Simple question

So this is a simple couple questions, here they are:
. How is DNA read off? Is it split into it's constituent strands by DNA helicase and then read by polymerase?
.But how does the triplet code work? Does it read 1 base from the left strand, 1 from the right, 1 from the left (alternate), or does it read three off from, say, the right one.
But if that were the case, wouldn't it mean the left strand could "get in the way", like surely the polymerase could read that by mistake and produce the wrong amino acids and proteins?
Anyone understand where I'm coming from?
Original post by Danny.L
So this is a simple couple questions, here they are:
. How is DNA read off? Is it split into it's constituent strands by DNA helicase and then read by polymerase?
.But how does the triplet code work? Does it read 1 base from the left strand, 1 from the right, 1 from the left (alternate), or does it read three off from, say, the right one.
But if that were the case, wouldn't it mean the left strand could "get in the way", like surely the polymerase could read that by mistake and produce the wrong amino acids and proteins?
Anyone understand where I'm coming from?


I'm not entirely sure what you're getting at here but I'll try and answer.

By DNA "read off" do you mean transcription? If that is the case it unzips using DNA helicase and then the template strand is used to create a strand of mRNA using RNA polymerase.

For transcription the triplet code is essentially irrelevant. All that matters is the promoter and terminator region. RNA polymerase recognises the promoter, binds and then transcribes all the DNA between and then stops at the terminator sequence.

In terms of "reading" only one strand is used and the other strand can't just get in the way because RNA polymerase must be bound to it which it isn't.

If you're asking about DNA replication my answer is pretty much the same except replace RNA polymerase with DNA polymerase, initiator with origin and the fact that both strands are used as a template but both have their own separate DNA polymerases acting on them.

I hope that is what you were asking...if not please feel free to ask again.
Original post by Danny.L
So this is a simple couple questions, here they are:
. How is DNA read off? Is it split into it's constituent strands by DNA helicase and then read by polymerase?
.But how does the triplet code work? Does it read 1 base from the left strand, 1 from the right, 1 from the left (alternate), or does it read three off from, say, the right one.
But if that were the case, wouldn't it mean the left strand could "get in the way", like surely the polymerase could read that by mistake and produce the wrong amino acids and proteins?
Anyone understand where I'm coming from?

In answer to your second, the first codon to be read always codes for methionine. This makes it less likely for a gene to be read back to front. There may also be other mechanisms to prevent backwards reading that I don't know about.
Original post by morgan8002
In answer to your second, the first codon to be read always codes for methionine. This makes it less likely for a gene to be read back to front. There may also be other mechanisms to prevent backwards reading that I don't know about.


Actually a very important thing is to make sure translation occurs at the correct methionine codon. Methionine isn't only used as a start codon but as a normal amino acid as well so there are methods in place to make sure the correct AUG sequence is recognised (in eukaryotes it's the first AUG after a cap on the mRNA which is the start...in prokaryotes it's a sequence of bases that the ribosome recognises followed by an AUG which is the start).

Generally there is no problem with backward coding as there will be a very different structure at both ends. In eukaryotes you have the cap (an upside guanine) at the start end and at the other end a tail of about 200 adenines (which act like a fuse on a bomb, telling the cell how long the mRNA should survive within the cell)/
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Thanks guys (and girls), helped a lot :smile:

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