# DNA code and codon

I work as a highschool teacher and I believe that in most highschool textbooks in my country there is a lost-in-translation problem involving some molecular biology basics. It has spread to the point one starts to doubt his basic knowledge, so here it goes:

For example, let's say that a triplet in mRNA is: 5' AUG 3'

That triplet is named CODON. (no problem there)

The DNA that corresponds to it has two strand. One is coding or sense strand and contains the corresponding triplet 5' ATG 3' The other is non-coding or antisense strand and contains the triplet 3' TAC 5'

Highschool textbooks in my country say that the triplet 3' TAC 5' , therefore the non-coding strand, is the CODE. It makes no sense to me whatsoever, but I'd like to check it out since in English literature the term code is rarely used anyway and genetic code is usually presented as codons. Sometimes, when the list of DNA triplets is given (and it's always in 5'->3' direction since the information is read that way) it says "DNA codons". So, to sum it up - is the DNA CODE equal to triplets in the coding or the non-coding strand?

• I wonder why you put in parenthesis: "(and it's always in 5'->3' direction since the information is read that way)". Do you mean: even if might as well be the other direction that wouldn't answer the question? Apr 1, 2022 at 13:39

The non-coding strand is indeed not the coding strand as the name suggests. It is the template strand. The template strand serves as the strand from where the mRNA is constructed upon. The mRNA contains the complement of the template strand, and is ,in fact, the actual codon. This is also the reason why the other strand is called the coding strand, it's the complement of the template strand, which makes it essentially the same as the mRNA, except uracil is replaced by thymine.

DNA Strand section:

5'---A-T-G---3' => coding strand
: : :
3'---T-A-C---5' => template strand


mRNA formation:

5'---A-U-G---3' => mRNA strand
: : :
3'---T-A-C---5' => template strand

• are the coding strand and template strand synonyms? Apr 19, 2018 at 20:48
• @BenHughes Nope, but they are complementary to each other. It's both of those strands that make up DNA. During transcription, the two strands split and the mRNA strand forms taking one of them as a template (hence it's name template strand). The other one doesn't do anything, but has the same base pairs (T replacing U) as the mRNA, hence called the coding strand. Apr 24, 2018 at 9:22

In the English literature, a sequence like your 3' TAC 5' (when considered as the complement to a 5' ATG 3' or 5' AUG 3' codon) is typically called an anticodon. Most often this is in the context of a tRNA having an anticodon to a codon on an mRNA. See, for example, this page from Molecular Biology of the Cell or, similarly, this page from Berg's Biochemistry

Generally, code is used in molecular biology to refer to the conceptual mapping from a codon sequence to an amino acid (or meta function like STOP), or collectively to the whole set of such mappings. The latter kind of reference is more likely to use the longer name the genetic code.

• Very helpful you "bring up" anticodon. Are you sure that this term is not exclusively used in mentioned context of transfer-(t)-RNA? The question seems to be on coding/negative "strand" relating/corresponding to "template"/transcribing(cp. related answer by David) "strand". In that sense, the anti-codon of a t-RNA doesn't appear to be a "strand". Apr 1, 2022 at 13:34
• @PeterBernhard, I disagree with you about what the question is asking, which is exactly why I added my answer after Twisted Genes' answer, which does a fine job of explaining strands. The OP mentions strands only as a point of reference for the actual question, which occurs in the last large paragraph. I believe he is asking about the names for triplets, and in English they are 'codon' and 'anticodon', and not about strands. (I also discuss the usage of 'code' which is another aspect of the question.) 'Anticodon' is not used much, and probably does appear primarily in the context of tRNA. Apr 1, 2022 at 18:41
• Maybe "Anti-" ought to be (trying some irony) opposed to the wording of the question "...the non-coding strand, is the CODE. " As I found with David quoted above, it's very well a matter of linguistics, too. As you say in your second part of your answer, "Crick's CODE" refers to that eminent fact that the proteins of life are made from amino acids which there is THE code for, hence - to my mind - "coding" for what IS the code, and not for that template fabricating. Your second part is the answer, question not on difference codon/anticodon (you made me emphasize). Will read all your reference. Apr 2, 2022 at 10:53
• Would you agree with "anticodon" in a wider sense being in use for any sequence that complements what has been defined as codon? - One more example I suggest is "interfering" RNA that matches m-RNA which may be named "non-coding anti-codon"? - Is non-coding, i.e. are anti-codons always read from `3 to '5, even when, as genes, are found on the 5' to 3' -codon strand? Thank you. Apr 2, 2022 at 11:11
• Albert, The cell you quote, says, defining: "anticodon - Sequence of three nucleotides in a transfer RNA molecule that is complementary to a three-nucleotide codon in a messenger RNA molecule". In fact, the term seems to be restricted to the context of tRNA. Apr 2, 2022 at 11:17