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    Wuddup.

    A question in the AQA AS Biology textbook asks:

    'Lysozyme is an enzyme consisting of a single polypeptide chain of 129 amino acids. What is the minimum number of nucleotide bases needed to code for this enzyme?'

    Answer is 129 x 3 = 387. That's what it says in the answers.

    This is, I put 390, which is an extra 3 bases. I thought that at the end of every sequence there has to be a stop codon right? Is that, or is that not a amino acid? Or are they just assuming that we don't need to know that.
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    I may be wrong, but I think stop codon is included in this 129 mentioned. And if non, shouldn't the start codon be counted separately too? ;d
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    (Original post by maereth)
    I may be wrong, but I think stop codon is included in this 129 mentioned. And if non, shouldn't the start codon be counted separately too? ;d
    Well isn't the start one always methionine, which is an amino acid so that counts, but the stop code isn't an amino acid is it? So that wouldn't be included... or...?
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    Hmm, that's a difficult question then.. I think I learned about this and I would say it's 387, not even thinking that stop codon isn't an amino acid.. But I can't find any reliable sources now so can't help I'm afraid...
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    A stop codon encodes for no amino acid. That is the basis of chain length elimination in translation

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    that's what I thought, but you just have to forget about the start and stop code in the sequence, i think of it as all included when you times by 3. its always either times or divide by three in the questions
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    They give you 3 options, this would be either:

    387, 390, 393

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    I think the question is malformed, because you DO need the start and stop codons for the translation. That's an extra 6 bases right there: note how it says "minimum" number of nucleotide bases.

    A gene consists of two types of DNA regions: exons and introns. Exons are the bit of the code that stays on the mRNA when it goes for translation - the bit that codes for the amino acids, introns are the bits in between exons and are coded into the original RNA transcript but are 'chopped out'. You need the introns for coding, too, and they aren't translated into amino acids - hence why the questions asking for "minimum number": if you can ignore introns; you can certainly ignore start and stop codons. :yes:

    I think the above goes a bit beyond A level knowledge, and I've tried to keep it basic.

    I'd like to point out that the methionine coded for by the start codon is removed from proteins post-translation; it's only needed to start off the sequence, nothing more, so the first methionine is not one of those 129 amino acids. :no:
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    (Original post by Hype en Ecosse)
    I think the question is malformed, because you DO need the start and stop codons for the translation. That's an extra 6 amino acids right there: note how it says "minimum" number of nucleotide bases.

    A gene consists of two types of DNA regions: exons and introns. Exons are the bit of the code that stays on the mRNA when it goes for translation - the bit that codes for the amino acids, introns are the bits in between exons and are coded into the original RNA transcript but are 'chopped out'. You need the introns for coding, too, and they aren't translated into amino acids - hence why the questions asking for "minimum number": if you can ignore introns; you can certainly ignore start and stop codons. :yes:

    I think the above goes a bit beyond A level knowledge, and I've tried to keep it basic.

    I'd like to point out that the methionine coded for by the start codon is removed from proteins post-translation; it's only needed to start off the sequence, nothing more, so the first methionine is not one of those 129 amino acids. :no:
    I guess we were dealing while ignoring introns



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