How Many Different Kinds of Amino Acids are Known

Question

How many different kinds of amino acids are known?
A) Less than 5
B) More than 5 but not more than 8
C) More than 8 but not more than 15
D) More than 70
E) More than 20

Accepted Answer

There are 20 standard amino acids that are used by cells to synthesize proteins, indicating that the correct answer is "More than 20."