Protein synthesis is a process by which cells make protein for themselves. This term could also be used for protein translation only. But more often, it refers to multi-steps for making protein. The main difference between eukaryotic and prokaryotic protein synthesis is, eukaryotic mRNA molecules are monocistronic. Prokaryotic mRNA molecules are polycistronic.
Prokaryotic Protein Synthesis
In prokaryotes, mRNA molecules are polycistronic, that means they contain the coding sequence of many genes. Prokaryotic protein synthesis begins even before transcription of mRNA is finished and thus we call this phenomenon as coupled transcription-translation. mRNA processing in prokaryotes is not required because they do not have introns in them. But archaebacteria does contain intron.
This is the only prokaryote that contains introns. Ribosomes often line up when a strand of RNA is being transcribed. The rapid change from gene to mRNA to protein can only happen in prokaryotes and not in eukaryotes. Prokaryotic ribosomes are only 70S. So mRNA here, can be immediately translated after transcription.
Eukaryotic Protein Synthesis
Eukaryotic DNA has got introns unlike prokaryotic DNA and these introns do not code for anything. They must be first removed from mRNA and then they are transcribed to mRNA. Therefore, translation can occur. This is done by complexes of snRNPs. In eukaryotes, mRNA, therefore, has to undergo certain processing first, before it could be translated. Eukaryotes use ribosomes that are slightly larger and more complex during the process of translation. Eukaryotic ribosomes are 80S and this is their sedimentation number. Here mRNA molecules are monocistronic containing coding sequence just for one polypeptide.
- Prokaryotic protein synthesis uses 70 S ribosomes and eukaryotic protein synthesis uses 80 S ribosomes.
- In eukaryotes, protein synthesis occurs in the cytoplasm.
- In prokaryotes protein synthesis occurs before the transcription of the mRNA molecule is completed.
- In eukaryotes, most of the genes have introns but in prokaryotes, there are no introns.
- In prokaryotes, splicing does not occur but in eukaryotes, splicing occurs.
- Only two initiating factors are involved in prokaryotic protein synthesis but nine initiating factors are involved in prokaryotes.
- No poly-A tail is added to bacterial mRNA in prokaryotes but it is added in eukaryotes.
- No 5’G cap is formed in prokaryotes but it is formed in eukaryotes.