There are 20 Different Amino Acids

Question

There are 20 different amino acids. What makes one amino acid different from another?
A) different side chains (R groups) attached to a carboxyl carbon
B) different side chains (R groups) attached to the amino groups
C) different side chains (R groups) attached to an α carbon
D) different structural and optical isomers
E) different asymmetric carbons

Accepted Answer

The side chains (R groups) are different and attached to an α carbon, which is what makes one amino acid different from another. The carboxyl carbon and amino groups are the same in all amino acids.

Answer: D
 Some amino acids can exist as different structural or optical isomers. Structural isomers have the same chemical formula but different structures, while optical isomers have the same chemical formula and structure but are mirror images of each other. This also contributes to the differences between amino acids.