1
$\begingroup$

Does the sense strand or antisense strand of DNA code for the polypeptide product? I'm confused because I know the antisense strand is the template for mRNA but it has anti codons so I do not know how this would be the coding strand. Ok so what I was confused about is when you are getting the code for the amino acid you can look at the mRNA strand which is the same as the sense strand except uracil replaces thymine, this is why I thought the sense strand could have coded for the amio acid instead of the anti sense strand.(the question I was looking asked if its the antisense or sense strand)

$\endgroup$
  • $\begingroup$ I've tried to clean up your question and its title but, as you say, you are confused, and so is your question. I'll try to answer it. $\endgroup$ – David Jun 14 '16 at 21:24
  • $\begingroup$ Antisense/non-coding DNA strand as a template for RNA polymerase => mRNA (being identical to the sense/coding DNA except for T -> U). If the sense/coding DNA strand were the template for RNA polymerase you would get mRNA that is identical to the antisense/non-coding DNA (again, except for T -> U). You would not want that ... $\endgroup$ – AlexDeLarge Jun 15 '16 at 10:01
3
$\begingroup$

I would add this as a comment to your question but do not have enough reputation. A simple look at Wikipedia (which is a very good source for general questions like these) would have provided you with an answer. I just did this to see how long it would take if I did not know the answer. It was about 20-30 seconds.

Protein synthesis: Transcription

In transcription an mRNA chain is generated, with one strand of the DNA double helix in the genome as a template. This strand is called the template strand.

Template strand

Only one of the two DNA strands serve as a template for transcription. The antisense strand of DNA is read by RNA polymerase from the 3' end to the 5' end during transcription (3' → 5').

If I understand your confusion correctly, you also do not understand how the seemingly "non-coding" strand can be the "coding" one which seems to be a paradox. If this describes your confusion adequately you have to think of the semi-conservative replication of DNA. The "non-coding"/antisense strand is transcribed by the RNA polymerase into its complementary RNA sequence. As this sequence is complementary to the "non-coding" DNA strand, the mRNA sequence is identical (with U replacing T) to the "coding"/sense DNA strand.

$\endgroup$
  • $\begingroup$ I don't think your Wiikipedia links are the most useful ones for two reasons. First, the questioner asks about the terms 'sense' and 'antisense', for which there is a specific Wiikipedia page, whereas the ones you reference refer to something called the 'template' strand, which is not the term in the question. Second the diagram of transcription on those pages is quite dreadful: over-complicated with unnecessary and confusing three-dimensionality (which of course bears no relation to reality). Simple diagrams are both more honest and intelligible. $\endgroup$ – David Jun 14 '16 at 21:55
  • 1
    $\begingroup$ I do not agree. @Maria already said that in her (and that is also the way I see it) view antisense and template are corresponding. I am not a big fan of the sense vs. antisense DNA strand concept and find coding vs. non-coding way more intuitive (good that you mentioned that, though). However, she uses the term 'template' in the question, so I find it more natural to use that term to help her with her confusion (the way I understood it). To your second point: I think she grasped the process of transcription - therefore I did not really care for the diagrams. Point taken, though. $\endgroup$ – AlexDeLarge Jun 14 '16 at 22:50
  • $\begingroup$ — The poster has modified her question now and I have modified my answer. However I would say that I think ‘template’ is a particularly dangerous term to use in this context. In brief this is because 1. the fact that linguistically templates produce a copy, whereas at best one is producing a reverse complement; 2. DNA strands are actually templates for their complementary strands, rather than mRNA or protein. I will add a longer argument about this to my answer when I have a little time. $\endgroup$ – David Jun 15 '16 at 9:36
  • $\begingroup$ Referring to your argument of the bacterial genome I would say that template is the best term to use as both sense/antisense and coding/non-roding, as you say in your answer, are relative terms. The template can be both of those strands depending on the gene. You are right, however, that one needs to make clear that the copy is a reverse complement and not identical. To your second point: I would say that DNA strands are templates for both DNA and RNA. Looking forward to your argument. $\endgroup$ – AlexDeLarge Jun 15 '16 at 9:59
1
$\begingroup$

You ask initially about the “sense” and “antisense” strands of DNA. These terms are explained in the Wikipedia reference entitled ‘Sense strand’. This states what you appear to be already aware of, that:

“The sense strand is the strand of DNA that has the same sequence as the mRNA, which takes the antisense strand as its template during transcription…”

Transcription produces a reverse complement of the DNA strand transcribed, just as the antisense strand of DNA is a reverse complement of the sense strand of the DNA. Thus:

5' ...ATGTTT...TAA... 3' : DNA sense strand

3' ...TACAAA...ATT... 5' : DNA anti-sense strand (template for transcription)

5' ...AUGUUU...UAA... 3' : mRNA (translated)

N     MetPhe...End    C : Protein

Qualifying the use of ‘Sense strand’

There is a danger in using ‘sense strand’ of thinking or implying that it refers to the whole of the DNA — after all, the description of a circular bacterial DNA is that it has two strands. However the genes in a bacterial DNA do not have the same directionality, so one can (and should) only talk about the sense strand of the DNA specifying a particular gene.

Disfavoured alternatives to ‘Sense strand’ 1: Coding strand

In your original question you switched from talking about the sense and antisense strands to talking about coding and non-coding DNA strands, although you later removed this. I would argue against this usage. It is the mRNA that does the coding and is actually translated into protein. The DNA can only be regarded as sense or not in terms of conceptual translation. In practice it either serves as the template for transcription or its complement does. There is also the problem that if you call the opposite strand ‘non-coding’, there is a possible confusion with the use of that term for the untranslated regions of the (coding) mRNA.

Disfavoured alternatives to ‘Sense strand’ 2: Template strand

I dislike the use of ‘Template strand’ because the original and primary use of ‘template’ in relation to DNA is replication (not information content). Further, when used in relation to protein-codoning potential it is not immediately apparent to me (and, I would argue to anyone approaching the topic for the first time) which strand of DNA would be regarded as ‘template’.

In English the term template generally means a pattern, mould or former used as a guide to create objects of a similar shape. Its adoption to the molecular biology of nucleic acids involved a subtle change of meaning, as the article produced from the DNA template (the product strand — DNA initially) was not the same shape as the mould, but a complement to it. However, the complementarity rules of the bases meant that the information in the original was preserved (in a manner somewhat analagous to that of a printing plate), and the metaphor caught on as it conveyed a clear meaning. It should be emphasized that this meaning was in relation to DNA replication and transcription. Thus, generations of biochemistry students read in texts like Berg et al. that:

DNA Polymerases Require a Template and a Primer

(whereas RNA polymerase only required a template). Furthermore they could read (e.g. in Wikipedia) that:

DNA is made up of a double helix of two strands, and each strand of the original DNA molecule serves as a template for the production of the complementary strand…

So if you start talking about the template strand of DNA you are in trouble already.

But what would that mean in relation to transcription of mRNA? Here it is the anti-sense strand of the DNA specifying the gene that is physically serving as template for the mRNA. However to many it would seem counter-intuitive to call this the template strand, so that those who use the term cannot in fact agree how to do so. To quote S. Malloy:

“…one school argues that the strand copied into mRNA should be considered the template strand, but the other school argues that the opposite strand which reflects the sequence in the mRNA should be considered the template because the corresponding codons are copied into protein.”

It clearly makes more sense to use ‘sense’ and ‘anti-sense’.

$\endgroup$
  • $\begingroup$ I've updated my answer in the light of the updated question. $\endgroup$ – David Jun 15 '16 at 9:37
  • $\begingroup$ I've now completed my arguments on terminology. A bit OTT, but you don't have to read them to read my answer. $\endgroup$ – David Jun 15 '16 at 15:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.