Prokaryotic translation

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Translation is the process in cells by which messenger RNA is read by a ribosome, and by utilising tRNA a protein is built according to the genetic code of the mRNA. This varies between prokaryotic and eukaryotic cells. This is a summary of the prokaryotic process.

Contents

1 Initiation
2 Elongation
3 Termination
4 Recycling
5 See also

Initiation

The process of initiation of translation in prokaryotes.

The ribosome consists of three sites: the A site, the P site, and the E site. The A site in the point of entry for the amino acetyl tRNA. The P site is where the peptidyl tRNA enters the ribosome. And the E site is a site briefly occupied by the growing peptide chain as it exits the ribosome.

Initiation of transcription begins with the 50s and 30s ribosomal subunits dissociated. IF1 (initiation factor 1) blocks the A site, while IF3 blocks the E site and prevents the two subunits from associating. The 16s rRNA of the small subunit recognizes the ribosomal binding site 5-10 base pairs up stream of the start codon AUG. The settles onto the mRNA so that the P site is directly on the AUG start codon. tRNA-meti enters the P site, which at the time is the only site open since IF1 and IF3 are blocking the A and E sites. Note that prokaryotes differentiate between a AUG methionine and an AUG start codon. In the case of a start codon the tRNA-met is formylated and called tRNA-meti.

Elongation

As soon as the tRNA-meti enters the P site, IF1 and IF3 are released due to a confomational change. This conformation change opens the A site allowing the amino acetyl-tRNA to enter the ribosome. Now the P site contains the beginning of the peptide chain of the protein to be encoded and the A site has the next base to be added to the peptide chain. Now a peptide bond is formed between the pepetide chain on the peptidyl tRNA and the amino acetyl tRNA. After the formation of the peptide bond, the mRNA "ratchets" over three bases taking the newly elongated peptide chain. The chain briefly enters the E site then moves out of the ribosome as the ribosome continues to translate the remaining codons on the mRNA until the ribosome reaches a stop codon (UAA, UGA, or UAG).

Termination

As soon as the ribosome hits a stop codon, proteins called Release Factors triggers release of completed protein from the ribosome. The ribosome then dissociates, ready to begin initiation.

Recycling

Once the nascent protein is released in termination, Ribosome Recycling Factor and Elongation Factor G (EF-G) function to release the mRNA from ribosomes. This "recycles" the ribosomes for additional rounds of translation.

Prokaryotic translation

Initiation

Elongation

Termination

Recycling

See also