What is translation? Why is it important (in terms of this Anthropology class)? [translation/protein synthesis]

Expert Solution

Translation

It refers to the polymerisation of amino acids to form a polypeptide. The order and sequence of amin acids are defined by the sequence of bases in the mRNA.

The cellular factory responsible for synthesising protens is the ribosome. The ribosome consits of structurall RNAs and atbout 80 different proteins. In its inactive state,. it exists as two sub units, a large subunit and a small sub unit. Ribosomes have two sites for binding amino acyl tRNA, P-site (peptidyl site) and A-site (aminoacy). When the small subunit encounters an mRNA, the process of translation of the mRNA to protien begins.

The steps of transiation mechanism are:

(a) Activation of amino acids:

In the presence of enzyme aminoacyl - tRNA synthetase(E), specifc amino acid (AA) bind with ATP.
AA1 + ATP -----> AA1-AMP-E1 complex + PPi

(b) Charging of tRNA :

The AA1, AMP-E1, complex reacts with specifc 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
AA, +AMP-E, complex+ tRNA一一>AA1 -tRNA, +AMP+E1

(c) Formation of polypeptide chain : It completes in three steps :
(1) Chain intiation: It requires 3 intiation factors in prokaryotes and 9 initiation factors in eukaryotes.
*Binding of mRNA with smaller subunit of ribosomes (30S/40S)
30S +mRNA-30S-mRNA complex
In eukaryotes, there is formation of 40S-mRNA complex.
*Binding of 30S-mRNA with tRNA non-formylated methionine is attached with tRNA in eukaryotes and formylated in prokaryotes.
30S-mRNA + tRNA---30S-mRNA-tRNA,
* Attachment of larger subunit of ribosome. It is 50S in prokaryotes & 60S in eukaryotes.

2)Chain elongation :

After the formation of complete ribosome -mRNA-tRNA complex, an aminoacyl acceptor site (A-site) is established next to the P-site. It exposes mRNA codon next to the intiation codon. A new aminoacyl tRNA complex reaches the A-site and forms codon - anticodon bonding. This requires elongaton factor and energy ie., GTP. A peptide bond is formed between COOH group of frst amino acid (methionine) and NH2 group of second amino acid. If two charged tRNAs are 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. It is catalysed by enzymei peptidy transferase (a type of ribozyme -catalytic RNA i.e., 23S rRNA in bacteria and 28 SrRNA in eukaryotes). The elongation factors are required in this process. Translocation is movement of ribosome on mRNA. The ribosome move from codon to codon along the mRNA. Amino acids are added one by one, translated into polypeptide sequences dictated by DNA and represented I by mRNA.

A translational unit in mRNA is the sequence of RNA that is flanked by the start codon (AUG) and the stop codon and codes for a polypeptide. An mRNA also has some additional sequences that are not translated and are referred as untranslated regions (UTRs). The UIRs are present at both 5'-end before start codon and 3'end after stop codon. They are required for efficient translation
process.

(3) Chain termination: the termination of polypeptide is signalled by one of the three termination codon (UAA, UAG, UGA). A GTP - dependent factor known as release factor is associated with termination codon.

gladiator answered 5 months ago

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