A protease recognizes and cleaves a hexapeptide that contain

A protease recognizes and cleaves a hexapeptide that contains a positively charged side chain at the S1 site and an aromatic side chain at the S1\' site and histidine cannot be at either position. How specific is the protease? That is, it cleaves:

A) one out of possible 48,960,000 peptides

B) one out of possible 960,000 peptides

C) one out of possible 15,552 peptides

D) one out of possible 7,776 peptides

E) 1.5% of all possible hexapeptides

Solution

To Solve this problem we have should some basic knowledge of Probability

In question its mentioned that at S1 position there should be positively charged amino acid and at S1’ position there should be an aromatic side chain residue.

There are three positively charge amino acid i.e. Histidine, Lysine and Arginine and three aromatic side chain amino acid i.e. Phenylalanine, tryptophan and tyrosine.

Also, it\'s mentioned in the question that histidine should not be present in above-mentioned position. So the probability of amino acid at S1 position will be 2 and probability of aromatic amino acid at S1\' position will be 3. At the other four place, we can have any combination of amino acids from the pool of 20 amino acids. So probability will

2*3*20*20*20*20 out of one

one out of possible 960,000 peptides

So the answer will be B