Question

Cells that use the amino acids selenocysteine and pyrrolysine have

A) two more codons compared to other cells.
B) two more tRNAs compared to other cells.
C) two more aminoacyl-tRNA synthetases compared to other cells.
D) two more tRNAs and aminoacyl-tRNA syntheses compared to other cells.
E) inosine at the third position of their tRNA anticodons to accommodate these amino acids.

Answer 1

Cells that use the amino acids selenocysteine and pyrrolysine have two more tRNAs and aminoacyl-tRNA synthetases compared to other cells, as these amino acids require unique mechanisms for their incorporation into proteins.The correct option is D.

Step-by-step explanation:

Cells that use the amino acids selenocysteine and pyrrolysine have D) two more tRNAs and aminoacyl-tRNA syntheses compared to other cells. These unusual amino acids are incorporated into proteins via unique mechanisms.

Selenocysteine, which is encoded by the UGA codon (typically a stop codon), requires a specific stem-loop structure called the SECIS element for its insertion into proteins.

Similarly, pyrrolysine uses the UAG codon (another stop codon) and requires its gene, pyls, and a unique tRNA with a CUA anticodon.

Each of these amino acids requires its own transfer RNA (tRNA) with a unique anticodon (UCA for selenocysteine and CUA for pyrrolysine) and an associated aminoacyl-tRNA synthetase enzyme to attach the amino acid to its respective tRNA.

These unique mechanisms ensure these amino acids are properly recognized and incorporated during protein synthesis in organisms that use them.The correct option is D.