Describe the process of translation.
 

Translation refers to the process of polymerisation of amino acids to form a polypeptide.

The order and sequence of amino acids are defined by the sequence of bases in the $mRNA.$

The amino acids are joined by a bond which is known as a peptide bond.

Formation of a peptide bond requires energy.

Therefore, in the first phase itself amino acids are activated in the presence of $ATP$ and linked to their cognate $tRNA$ - a process commonly called as charging of $tRNA$ or amino- acylation of $tRNA$ to be more specific.

If two such charged $tRNAs$ are brought close enough the formation of peptide bond between them would be favoured energetically.

The presence of a catalyst would enhance the rate of peptide bond formtion.

The cellular factory responsible for synthesising proteins is the ribosome.

The ribosome consists of structural $RNAs$ and about $80$ different proteins.

In its inactive state, it exists as two subunits, a large subunit and a small subunit.

When the small subunit encounters an $mRNA$; the process of translation of the $mRNA$ to protein begins.

There are two sites in the large subunit, for subsequent amino acids to bind to and thus be close enough to each other for the formation of a peptide bond.

The ribosome also acts as a catalyst ( $23 S$ $rRNA$ in bacteria is the enzyme ribozyme) for the formation of peptide bond.

A translational unit in mRNA is the sequence of $RNA$ that is flanked by the start codon ($AUG$) and the stop codon and codes for a polypeptide.

An $mRNA$ also has some additional sequences that are not translated and are referred as untranslated regions. ($UTR$).

The $UTRs$ are present at both $5^{\prime}$-end (before start codon) and at $3^{\prime}$-end (after stop codon).

They are required for efficient translation process.

For initiation, the ribosome binds to the $mRNA$ at the start codon ($AUG$) that is recognised only by the initiator $tRNA$.

The ribosome proceeds to the elongation phase of protein synthesis.

During this stage, complexes composed of an amino acids linked to $tRNA$, sequentially bind to the appropriate codon in $mRNA$ by forming complementary base pairs with the $tRNA$ anticodon.