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    3' A T A G T A C C G C A T G T A C G G G C G A G A C A T T C G A G C A T T C A T 5'

This a Template DNA.

How to find the number of amino acids amino acids in the protein encoded by the above gene?

The answer is $7$.

My Try:

First I converted the above DNA to RNA and got

   5' U A U C A U G G C G U A C A U G C C C G C U C U G U A A G C U C G U A A G U A 3'

Then I found the start codon which is A U G

5' U A U C |A U G| G C G U A C A U G C C C G C U C U G U A A G C U C G U A A G U A 3'

From here I am not understanding how to proceed.

Can anyone please explain how to solve this?

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  • $\begingroup$ Short question: How does RNA translate into protein? $\endgroup$ – Chris Aug 5 '18 at 19:34
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Then you just have to read the codon until you reach a stop codon. There are three stop codon UAA, UGA and UAG. So, in your example..

             Start                                                   Stop
5' U A U C | A U G | G C G | U A C | A U G | C C C | G C U | C U G | U A A | G C U C G U A A G U A 3'

Your protein is therefore 7 amino acids long (incuding the starting methionine). The genetic code is enter image description here

Therefore the 7 amino acids are

Met Ala Tyr Met Pro Ala Leu

In case you are confused about having an AUG codon in the middle of an open reading frame, then you should have a look at the post Effect of a doubling of the start codon in a gene.

Of course, I assumed that the region is indeed transcribed and that the first AUG is indeed the start codon and not just a methionine in the middle of an open reading frame.

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  • 1
    $\begingroup$ Good answer, though perhaps you should include the first methionine as the N-terminus since it is not always cleaved and the answer given in the OP is 7. $\endgroup$ – canadianer Aug 6 '18 at 0:01
  • $\begingroup$ @canadianer Thank you! Edited. I did not know the methionine of the start codon was sometimes (often, usually?!) kept. $\endgroup$ – Remi.b Aug 6 '18 at 0:29
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Each protein-coding gene consists of coding and non-coding regions. Coding region, a.k.a CDS (see: Coding region and Open Reading Frame), is spanned between translation initiation site (TIS), and one of stop codons. Non-coding regions include introns and non translated regions (5'UTR or 3'UTR) in the exons.

You need to know first, if (and where) your DNA template contains the information about amino acids sequence. Does your DNA template is the protein-coding region only or do you have some non-coding parts (eg. introns).

(Short remark: Methionine can be also found within the amino acids chain, not only at TIS = not every methionine is a TIS)

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