Question

Dna initiation elongation and termination

Answer 1

Translation is a process by which the genetic code contained within an mRNA molecule is decoded to produce the specific sequence of amino acids in a polypeptide chain. It occurs in the cytoplasm following transcription and, like transcription, has three stages: initiation,elongation and termination.

Answer 2

Initiation

• Initiation of translation occurs at 5’ end of mRNA.

• During initiation mRNA first binds to the small subunit of ribosome in the presence of initiation factor.

• The start codon is AUG it codes for methionine in eukaryotic initiation site and formyl methionine in prokaryotic initiation.

Elongation

• A second tRNA charged with an amino acid enters the A –site, this is with the help of elongation factors.

• It pairs with second codon.

• Then the peptide bond is formed between the first and second amino acid.

• This bond formation is catalysed by the enzyme peptidyl transferase.

• During this linkage between the first amino acid and its t RNA is broken, this tRNA is unloaded from P–site and the second at the A–site is pulled to the P –Site along with mRNA then this process is known as translocation.

Termination

• When the aminoacyl tRNA reaches the termination codon like UAA, UGA and UAG, termination of polypeptide chain of amino acids occurs.

• This leads to the release of the polypeptide chain of amino acids and tRNA from the ribosomes.

• The ribosomes dissociates in to large and small sub unit at the end of protein synthesis.