Forum Senior
Joined: 21 Mar 2008
Posts: 376
Location: Montreal
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| thyristor wrote: |
| How come each aminoacid has several codes and how is it possible for a code like AAAA to appear in DNA? This allows amoinoacids to be placed wrong in the ribosomes. |
Codons are read in triplets to start with, and AAA codes for Lysine. Moreover, there is a ton of regulatory regions in DNA that control which regions are transcribed, then in eukaryotes you have processing of the mRNA ahead of time. Most of the genome consist of structural domains and repeated sequences that don't make proteins.
Now, there are 4 bases that commonly exist in DNA, a codon consist of 3 bases so that means there are 4^3, 64, possible codons. There are 20 common amino acids plus start codons and stop codons, that means that there is a surplus of possible codons. Two codons can code for the same amino acid, but they may interact with a different tRNA, thus you can have two different tRNA that carry the same amino acid but recognize different codons. Then there is the process of "wobble base pairing" where if a tRNA has a I base in the anticodon it can bind more than one type of base, this is what occurs with glycine where the codons GGU, GGC, GGA and GGG can all bind the tRNA with the anticodon ICC. |
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