Tuesday, September 18, 2012

  

1) Comparison between prokaryotic mRNA (polycistronic) and eukaryotic mRNA (monocistronic) 


- note that 5' UTR and 3' UTR is present in both prokaryotes and eukaryotes. The 5' UTR in prokaryote is important as it contains the Shine-Dalgarno sequence, while the 5' UTR in eukaryotes is important as it can regulate translation as regulatory proteins can bind to it and prevent binding of ribosomes so as to carry out translation.

 

- note that unlike the prokaryotes, there is RNA processing in eukaryotes. Hence eukaryotic mRNA contain the 5' GTP cap (important for recognition/binding by eukaryotic ribosome and prevent mRNA degradation) and the 3' poly A tail (facilitate export of mRNA from nucleus and prevent mRNA degradation)  








2) Another picture showing that the prokaryotic mRNA is polycistronic.

- The Shine-Dalgarno sequences (impt for recognition and binding of prokaryotic ribosomes) are in between the multiple start and stop codons on the prokaryotic mRNA.










 3) Another diagram that shows the Shine-Dalgarno sequences on prokaryotic mRNA more clealy.


- Since the prokaryotic mRNA has multiple ribosome binding sites called Shine Dalgarno sequences, thus can lead to the synthesis of several different polypeptides. This is unlike the eukaryotic mRNA with only one ribosome binding site/ start site, so it can only lead to the synthesis of one polypeptide.