Imagine that 1 L of a solution containing each of the 20 naturally occurring amino acids at 50 mM concentration each (total concentration of 1 M) is allowed to polymerize in a perfectly stepwise fashion such that at each step, a random amino acid can be incorporated into a growing polypeptide. The steps are repeated, until eventually the solution is only composed of 40-mers (and virtually all of the monomers have been used). What fraction of all 40-mers can possibly be present in this solution? Round your number to four decimal places. Avogadro's number is 6 × 10²³.

Question

Quizplus · Accepted Answer

The number of possible 40-mers is equal to 20?? or approximately 10?². If every 40-mer in the solution has a unique sequence, there will be 0.025 moles of different 40-mers made in this solution (since the total amount of monomer was 1 mole), which is equivalent to 1.5 × 10²² molecules. Thus, only about one out of every 10³? possible 40-mer peptides has been sampled in this solution. Even the whole universe does not have enough atoms to sample all possible sequences for a protein with 300 amino acid residues in this way.

Imagine That 1 L of a Solution Containing Each of the 20