Answer:
3816543
Step-by-step explanation:
20^15 or 3.28. 10^19
That is roughly equivalent to 4.3 billion times the world population today (in just 20 amino acids). The beauty of proteins is their complexity and seemingly infinite possible permutations. Moreover, a single polypeptide chain can have many different tertiary structures. Polypeptide chains can then join together to form quaternary structures. Among these proteins can be an antibody for ovarian cancer, an antimalaria haemoglobin or a antitoxin for heavy metals. There are just so many proteins we do not know yet.