Wisconsin Esthetics State Board Practice Test

How many common amino acids are there?

1. 20

2. 22

3. 24

4. 26

The correct answer is: 22

The correct answer is that there are 20 common amino acids. These 20 amino acids are the building blocks of proteins and make up the genetic code of most living organisms. They play crucial roles in various biological processes, acting as the foundations for protein synthesis. While there are additional amino acids known as "non-standard" amino acids, the common ones primarily refer to those encoded directly by the universal genetic code. The confusion around the number may arise from the fact that there are a few rare amino acids, like selenocysteine and pyrrolysine, which are incorporated into proteins in specific organisms and situations. However, they are considered exceptions and do not change the fundamental count of the 20 standard amino acids that are most widely recognized in biochemistry and molecular biology.