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(a) Describe aminoacylation of tRNA.

(b) Explain the process that takes place in the ribosomes when
mRNA makes its entry into it in a prokaryote.

(c) Due to transcription error, ATG codon of DNA is transcribed into
UAG in mRNA which translates a non-functional polypeptide
chain in the ribosome. Justify the statement.

 

 

 

 
 
 
 
 

Answers (1)

a) In the first phase itself, amino acids are activated in the presence of ATP and linked to their cognate tRNA–a process commonly called as charging of tRNA or aminoacylation of tRNA to be more specific. If two such charged tRNAs are brought close enough, the formation of a peptide bond between them would be favored energetically.

b) 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 a peptide bond.

For initiation, the ribosome binds to the mRNA at the start codon (AUG) that is recognized only by the initiator tRNA. 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. In the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.

c) Due to transcription error, ATG codon of DNA is transcribed into UAG in mRNA which translates a non-functional polypeptide chain in the ribosome. This means that due to transcription error i.e presence of G in place of C there will be a synthesis of incorrect protein. Since the codon, UAG stops codon and it will cause termination of the polypeptide chain synthesis.

Posted by

Priyanka Kumari

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