RNA Translation and Protein Synthesis
Translation refers to the process through which messenger RNA is translated into protein(Nair 2004). This does take place through the following steps; Initiation, Elongation and termination. This paper will discuss the process of elongation of poly peptides.Elongation of polypeptidesIt is important to highlight the process of initiation in order to make a clear and smooth transition to the elongation process. The initiation step involves the collection and assembly of the necessary components for the translation process (Nair 2004). These are; the initiation factors (IF1, IF2 &IF3), aminoacyl tRNA, GTP and messenger RNA. The ribosome has three regions i.e. the A, P and E site. These have different purposes (Meisenberg& Simmons, 2006). The A site acts as the site for the entry of the aminoacyl tRNA (Nair 2004). Formation of the peptidyl tRNA occurs at the P site of the ribosome. The E site acts as the site of exit of for the tRNA which has already given amino acid to the growing polypeptide chain(Meisenberg& Simmons, 2006).The process of elongation requires specific non-ribosomal proteins eg in E-coli these are EFs. This step begins with the binding of the appropriate aminoacyl-tRNA to the condon to the Ribosomes A site. The Aminoacyl-tRNA is a tRNA with the capacity to bind to an amino acid. This Aminoacyl-tRNA is able to base pair with the condon on the mRNA (Nair 2004). This requires the use of an elongation factor and a source of energy which in this case is GTP. The elongation factor-Tu (EF-Tu) and GTPase are necessary for this process to occur (Meisenberg& Simmons, 2006). Elongation starts after the arrival of the initiator tRNA at the P site resulting to opening of the A -site through a conformational change (Nair 2004). A new aminoacyl-tRNA is able to bind at the opened A site..The incoming amino-acyl is brought to the A site by an eEF-1a-GTP complex which is hydrolyzed to GDP soon after the t RNA is deposited (Meisenberg& Simmons, 2006). EF-tu and the bound GDP vacate the ribosome this is the proof reading mechanism that discourage misincorporation of near -cognate aa-tRNA (Meisenberg& Simmons, 2006). Now the Aminoacyl tRNA remains at the A site for peptide bond formation (Nair 2004). The peptide attached to the tRNA at the P site is then transferred to the amino group at the aminoacyl tRNA at the A site. This reaction is referred to as transpeptidation and is catalysed by Peptidyltranferase(Nair 2004). The A site now contains peptidyl-tRNA while the P site has a free tRNA (Meisenberg& Simmons, 2006). The free tRNA vacates the P site and the peptydyl-tRNA moves from the A site to the P site.
Translocation is the final elongation stage and is catalyzed by the GTP binding EF-G. Three nucleotides are moved by the ribosome towards the 3 end of the messenger RNA.. The ribosome then continues to translate the remaining condons on the mRNA as more aminoacyl-tRNA bind to the A site until the ribosome reaches a stop condon on mRNA.the ribosome is moved along the mRNA such that the next condon of the mRNA resides under the A site. The e EF-tu is released from the ribosome. The rate of ribosomal protein synthesis is about 20 amino acids per second and the error rate is about 1 for every 10000 amino acids. This process is then followed by termination where the synthesized protein is released from the ribosome.
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