Prokaryote and Eukaryote Protein Synthesis

There are several points of difference between eukaryote and prokaryote protein synthesis, although the basic process is the same in both.

(1) In Prokaryotes protein synthesis is carried out by 70S ribosomes with 30S and 50S subunits, while in eukaryotes the ribosome is 80S with 40S and 60S subunits.



(2) In most bacterial mRNAs translation begins while mRNA is being transcribed on DNA. Degradation of the 5’ end of mRNA can being even before the mRNA has been completely transcribed. In eukaryotes, after transcription, the mRNA goes out through the pores in the nuclear envelope to the cytoplasm where translation takes place on the ribosomes. Thus mRNA is not translated in association with DNA.

(3) Eukaryote mRNAs are largely monocistromic and have only a single functional site for the initiation of protein synthesis. Many bacterial mRNAs on the other hand are polycistronic and contain several initiation and termination sites.

(4) In eukaryotes the starting amino acid is methionine while in prokaryotes it is N-formylmethionine.

(5) In prokaryotes three initiation factors, IF-1, IF-2 and IF-3 are required for polypeptide chain initiation. In eukaryotes there is no equivalent of IF-1 and there are many more factors involved.



(6) In prokaryotes the elongation factors are EF-Tu, EF-Ts and and EF-G. In eukaryotes the factors are EF-1 and EF-2, of which EF-1 corresponds to EF-Tu + EF-Ts.

(7) In prokaryotes the release factors are RF-1 (for termination codons UAA and UAG), RF-2 (for UAA and UAG) and RF-3 with stimulatory activity. In eukaryotes a single release factor RF recognized the three termination codons.