Question

explain process of translation

Answer 1

Answer:

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Explanation:

In short, translation is the synthesis of proteins by ribosomes in the cell. It follows after the process of transcription in which a molecule of mRNA is copied from DNA to produce a specific base sequence. ... This process is repeated until a stop codon on the mRNA is reached and the completed polypeptide is released.

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Answer 2

Answer:

Translation

It is the mechanism by which the triplet base sequences of mRNA molecules are converted into a specific sequence of amino acids in a polypeptide chain. It occurs on ribosomes.

The major steps are :

(a) Activation of amino acids : In the presence of enzyme aminoacyl - tRNA synthetase (E), specific amino acids (AA) bind with ATP.

$\sf AA_1 + ATP \xrightarrow{E_1,Mg^{2+}} AA_1 - AMP -E_1 \ complex + PP_i$

(b) Charging of tRNA : The $AA_{1} -AMP-E_{1}$ complex formed in first step reacts with a specific tRNA. Thus, amino acid is transferred to tRNA. As a result, the enzyme and AMP are liberated. It is also called as aminoacylation of tRNA.

$\sf AA_{1} - AMP - E_{1} \: complex + tRNA_{1} \longrightarrow AA_{1} -\underbrace{tRNA_{1}}_{Charged \:tRNA} + AMP + E_{1}$

(c) Formation of polypeptide chain : It is completed in three steps :

(i) Chain Initiation : It requires three initiation factors in prokaryotes.  Nine intiation factors are required in eukaryotes. The cellular factory responsible for synthesising  proteins is the ribosome. The ribosome consists of structural RNA and about 80 different proteins. In its  inactive state, it exists as two subunits, a large subunit and a small subunit.

(a) Binding of mRNA with smaller subunit of ribosomes (30S/40S).

(b) Binding of 30S/40S-mRNA complex with tRNA. Non-formylated methionine is attached with tRNA in eukaryotes and formylated methionine in prokaryotes.

$\sf 40S/30S -mRNA \ complex + tRNA_{met} \xrightarrow{GTP} 40S/30S-mRNA-tRNA_{met} \ complex$

(c) Attachment of larger subunit of ribosomes.

(ii) Chain elongation : Ribosomes have two sites for binding amino acyl tRNA (i) Amino acyl or A site  (acceptor site) (ii) Peptidyl site or P site (donor site). A second charged tRNA molecule along with its  appropriate amino acid approaches the ribosome at A site close to the P site. Its anticodon binds to  complementary codon of mRNA chain. A peptide bond is formed between COOH group of first amino acid  (methionine) and $NH_{2}$ group of second amino acid. The formation of peptide bond requires energy and is  catalysed by enzyme peptidyl transferase (23S rRNA in bacteria and 28S rRNA in eukaryotes). The initiating formyl methionine or methionine tRNA can bind only with P site. All other newly  coming aminoacyl tRNA bind to A site.Translocation is movement of ribosome on mRNA.

(iii) Chain termination : The termination of polypeptide is signalled by one of the three terminal codons in  the mRNA. The three terminal codons are UAG, UAA and UGA. A GTP-dependent factor known as  release factor is associated with termination codon. It is $eRF_{1}$ in eukaryotes and $RF_{1}$ and $RF_{2}$ in  prokaryotes.

At the time of termination, the terminal codon immediately follows the last amino acid codon. After this the polypeptide chain, tRNA, mRNA are released and the subunits of ribosomes get dissociated.