Question

1. E. Coli have been genetically modified to create tRNAs that recognize stop codons.
   1. Name an example of a tRNA that is normally not encoded into E. Coli. What stop codon does it target, and what modified amino acid does it have on its tRNA?
   2. Why is encoding a mutant amino acid beneficial for studying proteins?
   3. Why would encoding a mutant amino acid also be beneficial to make modified proteins?

Answer 1

a) stop codons and their modified amino acids-

1. UGA- selenocysteine

2. UAG- pyrrolysine

b) Encoding a mutant amino acid is beneficial to study protein functioning and important amino acids involved in it . Protein function is dependent on its structure and a changed or modified amino acid will alter the structure and hence, the function identifying essential amino acids.

c) Mutant amino acids code for different amino acids than normally present in a protein, forming modified amino acid. These proteins can be produced to have higher activity, higher substrate specifity and other functions.