The Synthesis of polypeptide chain - Translation

 

With the reference of central dogma,  When DNA is transcribed into a messenger RNA  during  transcription, the mRNA is  translated into a polypeptide chain or  protein by the process of  translation .

In translation, mRNA along with  tRNA and ribosomes work together to produce proteins. This is called Protein synthesis and takes place in cytoplasm. 

During transcription after the splicing, messenger RNA has been modified  from hnRNA and involved in  translation. It binds to a small subunit of the ribosome..

Ribosomes  have two subunits,  a large subunit and a small subunit. Both subunits are united with each other by the Magnesium ions.  They contain a binding site for mRNA  at a smaller subunit and two binding sites for tRNA located in the large ribosomal subunit. The process of protein synthesis includes three major steps Initiation, Elongation and termination.

The first step of protein synthesis is charging of tRNA molecules. This step  is catalysed by an enzyme called aminoacyl synthetase and ATP. This step is also known as aminoacylation of tRNA.

As mRNA molecules are encountered with a smaller subunit  of the ribosomes than a tRNA  molecule is also attached with the larger Subunit of ribosomes. tRNA molecules make interaction with the mRNA molecule according to the base pair or genetic code  present on mRNA.

As tRNA molecules make interaction with the  initiation Codon or  AUG  then  the process of translation begins. This step is called initiation.

As as the charged tRNA molecule pick up amino acid by  its amino acid acceptor end than renders the amino acids   according to base pairs  present on  mRNA. Amino acids are enter through the A Site and exited from P Site. After the initiation as first amino acid is rendered  by tRNA at a large subunit of the ribosomes. The smallest unit of the ribosomes flanks with the mRNA molecule  and  next tRNA molecule picks up next amino acid and also left it  at larger Subunit of ribosomes.

Amino acids are  joined at the larger subunit of ribosome by the peptide bond. The  formation of peptide  bond  is catalysed by the enzyme peptidyl transferase which is also present at the largest subunit of the ribosomes.The process of joining of amino acid is catalysed by peptidyl transferase enzyme and synthesis of polypeptide chain  takes place. This step is called elongation.

tRNA molecules join amino acids in a continuous manner  according to the codon  present on mRNA. As  the termination codon UAA or UAG or UGA is approached then the process of protein synthesis is terminated. And a newly synthesised protein chain is released from cytoplasm. 

There are so many genetic codes that are not translated during the protein synthesis. These are known as untranslated regions or UTR. This untranslated region is present on both 3 Prime and 5 prime ends.