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Prokaryotic Translation - The pathway of protein synthesis is called translation because the language of the nucleotide sequence on the mRNA is translated into the language of an amino acid sequence

The mRNA is translated from the 5 end to its 3 end producing a protein.

Prokaryotic mRNAs often have several coding regions, that is, they are polycistronic.

Each coding region has its own initiation codon and produces a separate species of polypeptide. Prokaryotic translation resembles that of eukaryotic translation in most of the detail except with minor changes.

Initiation:In prokaryotes, the ribosome 70S instead of 80S is used in translation machinery. In prokaryotes, the first amino acid, the one that initiates protein synthesis, is always the same. N-formyl methionine (Met). N-formyl methionyl-tRNA forms in two steps. First, ordinary methionine binds to a special tRNA, then the methionine on the tRNA receives the formyl group.

This unique amino acid participates only in initiation. It never goes into the interior of a polypeptide. In E. coli, a sequence of nucleotide bases (5' -UAGGAGG -3 ') known as the Shine Dalgarno sequence is located 6 to 10 bases upstream of the AUG codon on the mRNA molecule, that is, near its 5' -end.

The 16S ribosomal RNA component of the 30S ribosomal subunit has a nucleotide sequence near its 3 -end that is complementary to all pan of the Shine Dalgarno sequence.

Therefore, the mRNA 5 -end and the 3 -end of the 16S ribosomal RNA can form complementary base pairs, thus facilitating the binding and positioning of the mRNA on the 30S ribosomal subunit.

Elongation: During elongation, prokaryotes use EF-TU instead of eEF-la for catalysis, whereas for translocation they use EF -G instead of eEF-2.

Interestingly, many ribosomes can translate the same mRNA molecule simultaneously. Because of their relatively large size, the ribosome particles cannot attach to an mRNA any closer than 80 nucleotides apart. Multiple ribosomes on the same mRNA molecule form a polyribosome or polysome.
 

 
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