Question

(a) Write the specific features of the genetic code AUG.
(b) Genetic codes can be universal and degenerative. Write about them, giving one example of each.
(c) Explain aminoacylation of tRNA.

Answer 1

(a) AUG codes for methionine and is the initiator codon.

(b) Some amino acids are coded by more than one codon and hence the code is degenerate. For example, phenylalanine or Phe is coded by UUU as well as by UUC.

The code in nearly universal, meaning, from micro-organism to human beings, the codon would code for the same amino acid. For example, UUU would code for Phe from bacteria to human (though some exceptions are found in mitochondrial codons and in some protozoans).

(c) Aminoacylation of tRNA is the first phase of translation where amino acids are activated in the presence of ATP and linked to their cognate tRNA. An aminoacyl tRNA synthetase is an enzyme that attaches the appropriate amino acid onto its tRNA. Enzyme and AMP are released. tRNA complexed with an amino acid is sometimes called charged tRNA. The amino acid is linked to 3'-OH end of tRNA through its -COOH group.

AA-AMP + t + tRNA --> AA-tRNA + AMP + Enzyme