Question

1. Translation work is an essential step for protein synthesis. In order for the protein to be synthesized what must be recognized first in translation? How does this important part in translation have an effect on the rest of the reaction? Please provide a valid argument. Be as detailed as possible.

Answer 1

Before the Initiation of Translation, firstly, activation of amino acid and attachment to tRNA occurs. Aminoacyl-tRNA synthetases ( amino acyl tRNA ligase) activate amino acids by covalent linkage to tRNAs. Now this becomes aminoacyl-tRNA. This reaction involves to steps :

Amino acid + ATP ---> aminoacyl-AMP + PPi

Aminoacyl- AMP + tRNA -----> aminoacyl- tRNA + AMP

Now tRNA is called to be as acylated or charged.

Initiation:

Initiation involves binding of small ribosomal subunit to mRNA and then joined by larger sub unit. Then occurs Elongation and Termination.

Initiation requires the participation of several factors called as initiation factors. Eubacteria has three initiation factors : IF-1, IF-2, IF -3.

IF-1 :- Binds over A site of small ribosomal subunit.

IF-2 :- Directs the initiator tRNA to its correct position in the initiation complex. It works in the presence of GTP.

IF-3 :- binds to free 30s subunits and prevents premature reassociation of the large and small subunits of the ribsome. Its second function is to control the ability of 30S subunits to bind to mRNA . It also selects the initiator tRNA.

Initiation factors are basically there to activate or slow down or repress the translation process. These are present in both prokaryotes and eukaryotes.

°° Both subunits of ribosome bind to ribosome binding site, that is a short nucleotide sequence that precedes the coding region, to form complete ribosome. The ribosome binding site includes the upstream Shine- Dalgarno sequence and the initiation codon. Shine- Dalgarno sequence is short sequence 5'- AGGAGGU- 3' is about 10 nucleotides upstream of initiation codon.