Question

a. Tetracycline is a common medication used to treat bacterial infections. It prevents the aminoacyl-tRNA from binding to the ribosomal subunit. Describe the effect on the cell.

b. The wobble hypothesis predicts that fewer than 61 tRNA molecules are required to read the 61 sense codons. State the minimum number required. Explain.

Answer 1

a) Tetracycline block the binding of the aminoacyl-tRNA, to the A site of the ribosome and instead, tetracycline bind to the A site as it mimic the structure of aminoacyl-tRNA. But, the tetracycline after binding to the ribosome, only acquire the place in the large subunit of the ribosome, instead of bothe larger and smaller subunit making bit loosely bound to the ribosome. So, when the nascent peptide is shifted over the tetracycline, the complex gets detached from the ribosome, resulting truncated copy of the proteins. As the proportion of truncated protein/ full length protein increases, it will be very difficult for the cells to perform basic metabolic activities and their life become compromised.

B) The codon is consist of 3 bases and there are total 4 types of bases present in our body. So, total of (4*4*4) = 64 different codons are possible and to recognize each of these codons, a total of 64 tRNA molecules are required. But, the Wobble hypothesis says that the actual number of tRNA present is lesser than 64. It is possible because, the third base of the codon doesn't take part for specifying the incorporation of the amino acids, it will only depends on first two bases. So, in principle, minimum tRNA molecules required = (4*4) = 16.