biochemistry: Protein Synthesis
posted by mae .
1. Assume that a particular microorganism has 50 distinct trna molecules, and that it has 100 copies of each type of trna. Further assume that average number of nucleotides in each trna is 80. What is the energy cost, expressed as number of phosphoric anhydride bonds destroyed during the synthesis, to synthesize these 100 copies of these 50 different trna molecules?
This is what I did, I'm not sure it's right: ATP's, 2 per amino acid in the polypeptide (100); GTP's, 1 per initiation event (1) and 3 per subsequent amino acid (150) =251 all together, I think. Do I have to convert it to kcal/mol?

Well, heres what I would do. If 2 ATP's per amino acid, then we need to determine how many amino acids there are total. If there are 50 distinct tRNA molecules, and 100 copies of each, then there are a total of 50 x 100 = 50,000 tRNA molecules. Now if the average tRNA molecule has 80 nucleotides, then the total number of nucleotides is 50,000 x 80 = 4,000,000 amino acids. Now you can multiply this number by 2, which would give 8,000,000 phosphoric anhydride bonds is the energy cost, you do not need to convert to anything since the question does not ask of you to.