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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance4 Marks
Question
Describe the process of translation during protein synthesis
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Answer

→ Prokaryotic Translation involves following step.
(i) Activation of amino acid
(ii) Formation of polypeptide chain
→ Activation of amino acid
→ In the presence of aminoacyl tRNA Synthatare (Enzyme), a specific amino acid reacts with ATP
→ Amino acid + ATP + Enzyme $\xrightarrow{ Mg ^{2+}}$ Amino acid amp Enzyme (complex) + PPi
→ In aminoacylation of tRNA, the a.acid AMP - E (complex) reacts with uncharged t-RNA.
→ Amino acid - AMP (complex) - Enzyme + t-RNA → Amino acid (Charged) - t-RNA + Enzyme + PPi
→ Formation of Polypeptide chain
→ The cellular factory responsible for synthesising proteins is the ribosome.
→ The ribosome consists of structural RNAs and about 80 different proteins.
→ In its inactive state, it exists as two subunits; a large subunit and a small subunit.
→ When the small subunit encounters an mRNA, the process of translation of the mRNA to protein begins.
→ There are two sites in the large subunit, for subsequent amino acids to bind to and thus, be close enough to each other for the formation of a peptide bond.
→ The ribosome also acts as a catalyst (23S rRNA in bacteria is the enzyme - ribozyme) for the formation of peptide bond.
→ 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 traslated and the referred as untranslated regions (UTR). The UTRs are present at both 5'-end (before start codon) and at 3'- end (after stop codon). They arerequired for efficient translation process
→ Translation has 3 steps
• Initiation
→ For initiation, the ribosome binds to the mRNA at the start codon (AUG) that is recognised only by the initiator tRNA.
• 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
→ At the end, a release factor binds to the stop codon, termination translation and releasing the complete polypeptide from the ribosome.
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