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Sense/antisense - codon/anticodon - DNA/mRNA/tRNA - confused

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Sense/antisense - codon/anticodon - DNA/mRNA/tRNA - confused

Postby Julie5 » Wed Apr 27, 2011 7:11 pm

Hi - I'm seeking clarification on the distinction between sense/anti-sense and codon/anticodon.

A codon is the triplet code, and carries the sense of the gene (ie, it IS the code)(well, one amino acid thereof!)

An anti-codon is the complement to the codon, and carries the anti-sense of the gene.

BUT, I'm getting confused as to how this maps to the two DNA strands (template and coding) and thence to the mRNA and tRNA.

Is the logic: The tRNA carries the amino acid, so its triplet must therefore be the 'sense' one - which would mean the mRNA must have the anti-sense triplet, which means it must copy the sense triplet off the DNA, and so the sense-triplet (ie, codon) is on the coding strand of DNA ???

OR, is the logic: The mRNA carries the sense, so it copies the antisense (template) strand of DNA, while the sense/coding DNA is not copied. The tRNA complementary to the sense mRNA is in fact anti-sense, and the amino acids are therefore carried on anti-sense tRNAs.

I think these are the only two options???

Very many thanks for any clarification

Regards, Julie
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Postby Babybel56 » Wed Apr 27, 2011 7:36 pm

In theory both strands can be sense - it depends on context. For protein synthesis the sense (or positive +) strand is the template from which the protein can be constructed. So in this case it's the mRNA extracted from the nucleus and presented in the ribosomes. The antisense strands are just defined as the opposite complementary set, and so those on the tRNA attached to amino acids.

The sense strand of mRNA is, as you rightly say, copied from genomic DNA, so the strand from which it's derived is therefore an antisense strand, because it cannot be used to generate a protein polymer.

Or I could have saved you some time and just said: number 2!
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Postby JackBean » Wed Apr 27, 2011 7:41 pm

Julie, the second option is correct ;)

Cis or trans? That's what matters.
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Postby Julie5 » Wed Apr 27, 2011 8:34 pm

Thank you both so much! So, if I can just drill 'sense is mRNA' into my skull, I can then work out in either direction (back to transcription or on to translation) what is sense/antisense in DNA and the tRNA.

Now I just have to think up a mnemonic!

Much obliged - regards, Julie
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