Simply put - How does Amino acid activation work?

Different Amino Acids attach themselves to the corresponding molecules of tRNA, but they all have the same binding sites!!!

I don't believe there is a simple answer to this- so if you believe there is the question has most probably been misconstrued.

Please let me know what you think & I'd be happy to expand on the specifics of the question.

That's a good observation. I'll do my best to provide an answer. Here goes:

Although amino acids all bind to the tRNA via the carboxyl group (COOH) which is exactly the same in all amino acids, the activation process is done by an enzyme called the aminoacyl-tRNA synthetase. These enzymes are specific to each amino acid - so in most cells, there are 20 synthetases just as there are 20 amino acids.

To ensure accuracy in linking the correct amino acid with the correct tRNA, an aminoacyl-tRNA synthetase has two steps of discrimination. First, the correct amino acid will have the highest affinity to the active-site pocket than any of the other 19 amino acids. However, some amino acids will be too similar to be distinguished this way, so the enzyme has another step of discrimination. This second step involves an editing pocket where an incorrect but similar amino acid will be removed from the enzyme. The correct amino acid will be rejected from this editing pocket. This two-step mechanism allows for an accuracy of only one mistake in 40000 couplings.

On the other hand the aminoacyl-tRNA synthetase must also recognise the correct tRNA. Most synthetases will do this by recognising the anti-codon but some will do so by recognising nucleotide sequences of the acceptor stem. In other words, most synthetases will read several different positions of the tRNA.

I  hope this helps. But please DO ask more if this wasn't what you had in mind;)

Last edited by Manabu Sakamoto (13th Mar 2007 11:35:00)