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Two questions regarding finding the DNA sequence of a amino acid sequence (AA):

1) If you are able to find out the mRNA sequence of an AA, then don't you automatically know the DNA sequence?

2) When determining the mRNA sequence of an AA, how do you account for the various permutations in the genetic code for a given AA. Ex. Leucine is CUU and CUC. Or does it not matter?

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closed as off-topic by MattDMo, AliceD, rg255, Chris Mar 20 '16 at 21:00

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework questions are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy." – MattDMo, AliceD, rg255, Chris
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 1
    $\begingroup$ Homework questions and trivial questions about basic biological concepts are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy. $\endgroup$ – MattDMo Mar 19 '16 at 0:01
  • $\begingroup$ @MattDMo This is not a homework question. I am just curious about the answer based on a lecture I attended and couldn't grasp. Thanks for the help $\endgroup$ – Kevin Fernandes Mar 19 '16 at 13:30
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For 1, that is how retroviruses such as HIV work, and of which scientists have utilised to use in gene therapy. It requires a process called reverse transcription. However, this would only show you the gene the mRNA was from, but no information about its location, or if it is repeated elsewhere.

As for 2, this is to do with the fact that one base cannot code for one amino acid; as there are 20 common amino acids used to make proteins. With 2 bases, you are only getting 16 possible codes from the various base pairs you can create. However, with 3 bases, 64 possible combinations are possible, more than enough to suffice for the 20 needed. This is called the triplet code; and therefore, there are more possible combinations of the base pairs in DNA than there are amino acids to be made from them. The 'left over' combinations can code for the same amino acids as other combinations, making it the code degenerate. Therefore, it doesn't matter, as the combination is always read in 3s (non-overlapping), and if it codes for a particular amino acid, then that amino acid will be produced at the ribosomes when its corresponding code is read.

I hope this increases your understanding of the topic.

http://www.genetherapynet.com/viral-vector/retroviruses.html (Question 1) http://www.chemguide.co.uk/organicprops/aminoacids/dna4.html (Question 2)

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  • $\begingroup$ Excellent! It definitely helps @Butallati For 1, is it every important to know where in the human DNA the gene if you have the mRNA sequence to make synthetic DNA? $\endgroup$ – Kevin Fernandes Mar 19 '16 at 20:28
  • $\begingroup$ Well, if we're talking about 'synthetic DNA', it's gonna be pretty difficult to create millions of pairs - so often scientists only create synthetic DNA in the form of genes, which are more...measurable. By taking the mRNA that you know will be used to produce a particular protein, and using a retrovirus, you will just be inserting that gene back into the DNA (just like how HIV will insert its own gene into your DNA, after all, it too is a retrovirus). Therefore the location of gene on the DNA is not particularly important for that instance. $\endgroup$ – Butallati Mar 19 '16 at 20:39
  • $\begingroup$ If you wish to know more on the uses of retroviruses in gene therapy, feel free to google about "SCID" and gene therapy. There may well be some processes, or maybe just general knowledge of how DNA works, which requires knowing the location of genes on DNA, however I personally don't know any. $\endgroup$ – Butallati Mar 19 '16 at 21:00
  • $\begingroup$ thanks so much for the exciting information! I'm a medical student whose eyes are just opening to the world of therapeutics and biotech start ups. Most of my experience has been in retrospective clinical research but I'll be taking a research year soon to expose myself to clinical trials and basic science work $\endgroup$ – Kevin Fernandes Mar 20 '16 at 14:58
  • $\begingroup$ Awesome, glad I could help. I'm just an A2 student (1 year prior to University), so it's nice to see possible applications of what I've learnt to this website. In addition to what I mentioned earlier, some other interesting things under the topic of DNA technology are the use of gene markers, in vivo gene cloning (using vectors such as retroviruses, as explained above) and in vitro gene cloning (using the polymerase chain recaction). Those should help further your understanding of DNA technology (which is closely related to your question) $\endgroup$ – Butallati Mar 20 '16 at 16:10

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