Approximately how many different amino acids are used in the synthesis of body proteins in humans?

• A. 22
• B. 12
• C. 20
• D. 9

Answer: (C)

Verified step by step guidance

1. Understand the context: Proteins are synthesized in the human body using amino acids, which are organic molecules that serve as the building blocks of proteins. The question asks about the number of amino acids involved in this process.
2. Recall the key concept: In humans, there are 20 standard amino acids that are directly encoded by the genetic code and used in protein synthesis. These are often referred to as the 'canonical' amino acids.
3. Clarify the distinction: While there are 20 standard amino acids, additional amino acids like selenocysteine and pyrrolysine (making a total of 22) are used in specific proteins but are not universally involved in protein synthesis. This is why the correct answer focuses on the 20 standard amino acids.
4. Eliminate incorrect options: The options '12' and '9' are incorrect because they do not represent the number of amino acids used in protein synthesis. Humans require 20 amino acids for this process.
5. Conclude the reasoning: The correct answer is 20 because these are the amino acids universally used in the synthesis of body proteins in humans, as encoded by the genetic code.