Translation in eukaryotes

Translation in eukaryotes

Translation process in eukaryotes also includes 3 steps which is almost similar to prokaryotic translation. The steps are: Initiation, Elongation and termination. The major difference in eukaryotic translation  are

1.      The initiator methionine is unmodified although a special initiator tRNA brings it to the ribosome.

2.      Shine Dalgarno sequences are not found in eukaryotic mRNA .In eukaryotes, AUG is embedded in Kozak sequence.

Inorder to bind AUG initiation codon,

1. Eukaryotic initiator factor eIF-4F-(a multimer of eIF-4E,Cap binding protein(CBP))binds to 5’ end of mRNA.

2. Scanning process of  initiator AUG codon, by a complex of 40S ribosomal subunit with initiator Met-tRNA and several proteins along with GTP and other  eIF along the mRNA. This process is called the scanning model for initiation.

3.Once,40S subunit binds to AUG ,60S subunit binds to it and releases all other  eIF except, eIF-4F  producing 80S initiation complex with Met-tRNA bound to mRNA in the P site of the ribosome.

4. poly(A) tail binding protein {PABP}bound to the poly(A) tail also bind to eIF-4G,one of the protein of eIF -4F at the cap and forms looping the 3’end of the mRNA.

In eukaryotes, the elongation step is almost similar that in prokaryotes. The main difference in number and properties of elongation factors  and in exact sequence of events.

1.      In eukaryotes, a single release factor (eukaryotic release factor one ) eRF1 recognizes all the three stop codons. eRF3 stimulates the termination events.

2.      Termination events are as follows:

3.     Release of polypeptide from tRNA in the P site of the ribosome by peptidyl transferase.
Release of tRNA from ribosome
Dissociation of two ribosomal subunits and release  RF from the mRNA
 Initiating amino acid Met is cleaved from the complete polypeptide
 

 

 


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