Compare and contrast to process of translation of mRNA into a protein on a

ribosome between prokariots and eukariots. Focus on the phases of initiation,

elongation, and termination, and the different factors that were involved in each of these

steps.

There are important differences in the process of mRNA translation between prokaryotes and Eukaryotes.

Explanation:

Initiation:

Prokaryotes:

The 30S subunit of the ribosome binds initiation factors 1 and 3 (IF1 and IF3) The shine dalgarno site (where binding of the ribosome occurs) at 5' end of the mRNA, is upstream of the start codon AUG, that leads into the open reading frame Initiation occurs at AUG, sometimes GUG but rarely at UUG Initiation tRNA carries a N-formyl-methionyl group 50S subunit binds, GTP is hydrolyzed to form GDP and the initiation factors are released

Eukaryotes:

There are 12 initiation factors Elongation factors 1A and 3 (ELF-1A and ELF-3) act in a similar manner to IF-1 and IF-3 There is no shine dalgarno site, instead the ribosome binds to the 5' end of the mRNA and glides down it to the first start codon (AUG); here initiation occurs Initiation only occurs at AUG The initiation tRNA is the normal methionine tRNA

Elongation:

Prokaryotes:

Charged tRNA binds to the EF-Tu and the tRNA-EF-Tu complex then binds to the A site on the ribosome GTP is hydrolyzed to form GPD and EF-Tu is released A peptide bond is created using peptidyl transferase activity in the 23S subunit of rRNA EF-G-GTP complex binds to the tRNA-peptide complex found at the A site GTP is hydrolyzed and the tRNA peptide moves from the A-site to the P-site

Eukaryotes:

The elongation factors are different to those found in prokaryotic tranlsation, however the process is the same

Termination:

Prokaryotes:

Slow process comparable to elongation and begins as soon as the open reading frame is reached, indicated by stop codons UAA, UAG or UGA Requires release factors (RFs) which are proteins, not tRNAs RF1-3 initiates termination RF1 recognizes stop codons UAA/UAG RF2 recognizes stop codon UGA RF3 is a GTPase, which aids in the removal of RF1 and RF2 post-termination

Eukaryotes:

Utilize eRF instead of RF1, RF2 and EF2-GTP instead of EF-G