• Question from:hunor

Hi there,

In most illustration I've seen, these tRNAs  are just swirling randomly around ribosomes and then they just happen to enter a ribosome in the right order.   It can't be that way, I guess ribosomes somehow sort these and let in only the one it actually needs in a given moment, or is there a buffer for tRNAs inside ribosomes? Could you enlighten me please:)

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  • Barts and the London, London
  • Posts: 268

tRNAs are present in the cytoplasm and do randomly encounter ribosomes synthesising proteins. They form fleeting bonds with the codons on the mRNA which do not last unless the tRNA is carrying the complementary anti-codon.

  • University of Waikato, Hamilton, New Zealand
  • Posts: 307

Hi hunor,

You have touched on one of the enduring problems with cellular biology; while we know about the process for docking of tRNAs during protein synthesis, the exact dynamics of delivery of amino-acylated (that means with an amino acid attached) tRNAs are still pretty much a mystery. This is because the machinery that surrounds ribosomes is not nearly as well studied as the ribosome itself.

Our best guess is what ReetikaSuri has already mentioned, random collisions; sometimes called "stochasticity", which basically means there is a certain probability for a given tRNA molecule to be found in the active site of the ribosome over a given timeframe. If the tRNA anticodon matches the mRNA codon being presented, the probability of that tRNA remaining in the active site for longer is increased. As the ribosome moves along the mRNA, the probability shifts to favour the various tRNA anticodons required until all of the mRNA codons have been read and the protein is finished.