How many standard amino acids are used to build proteins?

How many standard amino acids are used to build proteins?

• A. Catalysts for reactions in cells; 30 types
• B. Nucleotides; 4 types
• C. Building blocks of proteins; 20 types
• D. Carbohydrate monomers; 10 types

Answer: (C)

Proteins are built from amino acids, the building blocks arranged in long chains. The standard genetic code specifies twenty amino acids that are routinely incorporated into proteins during translation. These twenty differ by their side chains, which gives each amino acid distinct chemical properties and drives how the chain folds into three-dimensional structures with specific functions. While some organisms use a few nonstandard amino acids in particular contexts, the common, canonical set used to build most proteins is twenty. The other statements mix up what these building blocks are—nucleotides form nucleic acids, carbohydrate monomers form carbohydrates—so they don’t describe the building blocks of proteins or their quantity.

Proteins are built from amino acids, the building blocks arranged in long chains. The standard genetic code specifies twenty amino acids that are routinely incorporated into proteins during translation. These twenty differ by their side chains, which gives each amino acid distinct chemical properties and drives how the chain folds into three-dimensional structures with specific functions. While some organisms use a few nonstandard amino acids in particular contexts, the common, canonical set used to build most proteins is twenty. The other statements mix up what these building blocks are—nucleotides form nucleic acids, carbohydrate monomers form carbohydrates—so they don’t describe the building blocks of proteins or their quantity.