`star` Charging of tRNA
`star` Ribosomes
`star` Translation Unit
`star` 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 aminoacylation 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 formation.


● The `color{Violet}"cellular factory"` responsible for synthesising proteins is the `color{Violet}"ribosome"`.

● The ribosome consists of `color{Violet}"structural RNAs"` and about 80 `color{Violet}"different proteins"`.

● In its `color{Violet}"inactive state"`, it exists as two subunits; a `color{Violet}"large subunit"` and a `color{Violet}"small subunit"`.

● When the small subunit encounters an mRNA, the process of `color{Violet}"translation"` of the `color{Violet}"mRNA to protein"` begins.

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

● The ribosome also acts as a `color{Violet}"catalyst"` (`color{Violet}"23S rRNA"` in bacteria is the enzyme- `color{Violet}"ribozyme"`) for the formation of `color{Violet}"peptide bond"`.


● A `color{Violet}"translational unit"` in mRNA is the sequence of RNA that is flanked by the `color{Violet}"start codon (AUG)"` and the `color{Violet}"stop codon"` and codes for a `color{Violet}"polypeptide"`.

● An mRNA also has some `color{Violet}"additional sequences"` that are not translated and are referred as `color{Violet}"untranslated regions (UTR)"`.

● The UTRs are present at both `color{Violet}"5' -end"` (`color{Violet}"before start codon"`) and at `color{Violet}"3' -end"` (`color{Violet}"after stop codon"`).

● They are required for `color{Violet}"efficient translation"` process.


● For `color{Violet}"initiation"`, the ribosome `color{Violet}"binds"` to the mRNA at the `color{Violet}"start codon"` (AUG) that is recognised only by the `color{Violet}"initiator tRNA"`.

● The ribosome proceeds to the `color{Violet}"elongation phase"` of protein synthesis.

● During this stage, complexes composed of an `color{Violet}"amino acid linked to tRNA"`, sequentially bind to the `color{Violet}"appropriate codon"` in mRNA by forming `color{Violet}"complementary base pairs"` with the tRNA anticodon.

● The ribosome moves from `color{Violet}"codon to codon"` along the mRNA.

● Amino acids are added one by one, translated into `color{Violet}"Polypeptide sequences"` dictated by DNA and represented by mRNA.

● At the end, a `color{Violet}"release factor"` binds to the `color{Violet}"stop codon"`, terminating translation and releasing the `color{Violet}"complete polypeptide"` from the ribosome.