Process of Translation - Practice Questions & MCQ

• Translation refers to the process of polymerization of amino acids to form a polypeptide.
• The key components required for translation are:
  • mRNA 
  • ribosomes 
  • tRNA 
  • aminoacyl-tRNA synthetases. 
• During translation mRNA nucleotide bases are read as three base codons, each of which codes for a particular amino acid.
• Each tRNA molecule possesses an anticodon on the opposite end that is complementary to the mRNA codon. 
• tRNA molecules are therefore responsible for bringing amino acids to the ribosome in the correct order ready for polypeptide assembly.
• Aminoacyl-tRNA synthetases are enzymes that link amino acids to their corresponding tRNA molecules in a process called charging of tRNA or aminoacylation of tRNA.
• The resulting complex is charged and is referred to as an aminoacyl-tRNA.
• Each individual amino acid has an amino group (NH2) and a carboxyl (COOH) group.
• Polypeptides are formed when the amino group of one amino acid forms an amide (i.e., peptide) bond with the carboxyl group of another amino acid.
• This reaction is catalyzed by ribosomes and generates one water molecule.
• In prokaryotes, each mRNA molecule is simultaneously translated by many ribosomes, all synthesizing protein in the same direction: reading the mRNA from 5' to 3' and synthesizing the polypeptide from the N terminus to the C terminus. 
• The complete mRNA/poly-ribosome structure is called a polysome.
• In prokaryotes, three factors are involved in the initiation of translation [IF1, IF2 and IF3], one factor in the elongation of polypeptide chain and three factors in chain termination [RF1, RF2 and RF3].
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• Like transcription, translation has three stages: initiation, elongation and termination. 

Initiation:

• Initiation of translation in prokaryotes involves the assembly of the components of the translation system which are: 
  • the two ribosomal subunits (small and large), 
  • the mRNA to be translated, the first (formyl) aminoacyl tRNA (the tRNA charged with the first amino acid), 
  • GTP (as a source of energy), 
  • three initiation factors (IF 1, IF 2 and IF 3) which help the assembly of the initiation complex.

Elongation:

• The ribosome proceeds to the elongation phase of protein synthesis. 
• During this stage, complexes composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon. 
• The ribosome moves from codon to codon along the mRNA. 
• Amino acids are added one by one, translated into Polypeptide sequences dictated by DNA and represented by mRNA.

Termination:

• Termination of translation occurs when a nonsense codon (UAA, UAG, or UGA) is encountered. 
• At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.