Question

In: Biology

describe the elongation phase of translation.

describe the elongation phase of translation.

Solutions

Expert Solution

Elongation phase of translation in prokaryotes: It includes codon to codon translocation of active ribosomes on mRNA in 5'-3' direction and forms peptide bond between codon specified amino acid. There are three elongation factors namely:

  • EF-Tu: Transport charged tRNA from cytosol to the A site of the ribosome in GTP bound state.
  • EF-Ts: Act as guanine nucleotide exchange factor and regenerates EF-Tu.
  • EF-G: Mediate translocation of active ribosome from one codon to next codon (GTP dependent process).

Elongation includes three sub-steps:

  • Binding of aminoacyl tRNA (charged tRNA) to the A site of ribosomes: Binding of charged tRNA is catalysed by GTP bound EF-Tu. Once tRNA properly binds to the A site, EF-Tu release with GTP hydrolysis and generation of active EF-Tu is catalysed by EF-Ts by replacing GDP from GTP.
  • Peptide bond formation: After the release of EF-Tu amino group of A site amino acid act as nucleophile on carboxylic group of P site amino acid and makes peptide bond. After peptide bond formation P site tRNA becomes uncharged and A site tRNA generates dipeptidyl tRNA.
  • Translocation of ribosomes: After peptide bond formation ribosome translocate to next codon. Translocation shifts dipeptidyl tRNA from A site to P site and uncharged tRNA from P site to E site and A site occupy next codon thus open for incoming amino acyl tRNA (charged tRNA). Translocation reaction catalysed by ribosomes itself (without EF-G) but EF-G maintain translocation efficiency during translation.

Elongation phase of translation in eukaryotes: The mechanism is same as that of prokaryotes described above only the elongation factors changes, there are mainly three elongation factors in eukaryotes:

  • eEF-1 : Transport charged tRNA (aminoacyl tRNA) from cytoplasm to the A site of ribosomes and is a GTP dependent process.
  • eEF-1 : Regenerate eEF-1
  • eEF-2: Translocate ribosome codon to codon (GTP dependent process)

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