Multiple Choice
Which of the following functional groups is found in all standard amino acids?
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3. Amino Acids
Amino Acid Groups
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How many standard amino acids are commonly found in proteins?
A
18
B
22
C
16
D
20
Verified step by step guidance1
Step 1: Understand the context of the question. Proteins are composed of amino acids, which are organic molecules that serve as the building blocks of proteins. The question asks about the number of standard amino acids commonly found in proteins.
Step 2: Recall the definition of standard amino acids. These are the amino acids encoded directly by the genetic code and incorporated into proteins during translation. They are universally recognized in biochemistry.
Step 3: Note that there are 20 standard amino acids. These include examples like glycine, alanine, valine, and lysine, among others. These amino acids are encoded by codons in the mRNA sequence.
Step 4: Understand why the other options (18, 22, and 16) are incorrect. While there are rare amino acids like selenocysteine and pyrrolysine, they are not considered part of the standard set, which is limited to 20.
Step 5: Conclude that the correct answer is 20 standard amino acids, as this is the universally accepted number in biochemistry for proteins encoded by the genetic code.
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