What is the monomer building block of proteins?

• A. Fatty acids
• B. Monosaccharides
• C. Nucleotides
• D. Amino acids

Answer: (D)

Verified step by step guidance

1. Understand the concept of a monomer: A monomer is a small molecule that can join together with other similar molecules to form a polymer. In biology, polymers are large molecules made up of repeating units called monomers.
2. Identify the macromolecule in question: Proteins are one of the four major types of macromolecules found in living organisms, alongside carbohydrates, lipids, and nucleic acids.
3. Recognize the structure of proteins: Proteins are composed of long chains of amino acids. These chains fold into specific shapes that determine the protein's function.
4. Learn about amino acids: Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid has a central carbon atom, an amino group ($\mathrm{NH}2$), a carboxyl group ($\mathrm{COOH}$), and a unique side chain.
5. Connect the concept: Since proteins are made up of chains of amino acids, amino acids are the monomer building blocks of proteins. This distinguishes them from other macromolecules, which have different monomers such as monosaccharides for carbohydrates, fatty acids for lipids, and nucleotides for nucleic acids.