TRANSLATION

Translation can be defined as transfer of genetic information from mRNA to polypeptide is known as translation .

Translation can also be defined as  synthesis of protein from mRNA .

Translation occurs in cytoplasm along with protein synthesis 

Mechanism

1- Activation Of Amino Acids 

There are 20 types of amino acids present in cytoplasm .These are in inactive form .

They get activated by using ATP in presence of specific activating enzymes called amino acyl synthetase .This results in formation of amino acyl adenylate enzyme complex .

2- Transfer Of Activated Amino Acid To tRNA 

The amino acyl adenylate enzyme complex gets associated  with unpaired CCA  end of specific tRNA molecule .

An ester bond is formed between -COOH group of amino acid and -OH group of tRNA .

It result in formation of amino acyl tRNA complex and AMP is released AA-AMP enzyme + tRNA ...... AA-tRNA + AMP+ENZYME .

These are twenty specific tRNA for 20 specific amino acids.

3- Initiation  Of Polypeptide Chain 

Protein synthesis in initiated by initiation factors .There are three initiation factors in prokaryotes like IF1,IF2 ,IF3  similarly in eukaryotes there are nine initiation factors like  elF1 ,elF2 etc .

Ribosomes are scattered in cytoplasm as separated units .That means both the sub units are detached from each other 

elF2 or elF3 gets attached to the smaller subunits of ribosome . Cap part of mRNA gets attched to the ribosome in presence of GTP .Then bath the subunits are assembled to form 80s ribosome in eukaryotes and 70s ribosome in prokaryotes .

The larger sub-unit of ribosome has 3 rites .

These are p-site -peptide site 

A site - aminoacyl site and E-site-Exit Site 

The first amino acid tRNA complex gets attached to the p site i.e. AUG known as initiation codon 

The first amino acid formed in the process of translation is fermylated methionine incase of prokaryotes where as methionine in eukaryotes .

4- Elongation 

Next amino acyl tRNA complex complex comes to the A site and gets attached to mRNA with help of anticodon . This association requires GTP and two elongation factors EF-TS and EF-Tu 

Peptide bond is formed between the force carboxyl group of the first amino acid and the free amino group of the second amino acid .This reaction is catalysed by an enzyme peptidyl transferase present in larger sub-unit.

The incoming amino acyl tRNA complex moves to exit site from p-site i.e. outside the ribosome .It is released in cytoplasm .

The incoming amino acyl tRNA complex attched to A site known as amino acyl tRNA and the tRNA attched to site are called peptidyl tRNA due to formation of peptide bonds 

Then second amino acyl tRNA complex moves from A site to p site giving away space for next amino acid . This process is known as translacation .Here ribosome moves along mRNA from 5' -3' direction .

The A site is vacated a new codon enters this site and translocation is repeated 

5- Termination

Elongation of  polypeptide stops when moving ribosome come across three terminator codons like UAA ,UGA ,UAG .

In prokaryotes UAA and UAG are recognised by the releasing factor RF1 while RF2 recognised UAA or UGA 

RF terminator codon ribosome complex blacks further chain elongation .Then polypeptide chains reduced into cytoplasm and ribosomes gets dissciated from mRNA .