Which of the following statements is most true regarding proteins as macromolecules and their functions?

• A. Proteins are composed of monosaccharide units linked by glycosidic bonds.
• B. Proteins function mainly as long-term energy storage molecules.
• C. Proteins serve as enzymes, structural components, and signaling molecules in cells.
• D. Proteins are primarily responsible for storing genetic information.

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by identifying the basic building blocks of proteins. Proteins are composed of amino acids, not monosaccharides. Monosaccharides are the building blocks of carbohydrates, which are linked by glycosidic bonds. Proteins are linked by peptide bonds formed between amino acids.
2. Step 2: Evaluate the statement about proteins functioning as long-term energy storage molecules. Proteins are not primarily used for energy storage; this role is typically fulfilled by lipids (e.g., triglycerides) and carbohydrates (e.g., glycogen). Proteins have more specialized roles in the cell.
3. Step 3: Analyze the statement that proteins serve as enzymes, structural components, and signaling molecules. This is accurate. Proteins act as enzymes to catalyze biochemical reactions, provide structural support (e.g., collagen in connective tissues), and function in cell signaling (e.g., hormones like insulin).
4. Step 4: Examine the statement that proteins are responsible for storing genetic information. This is incorrect. Genetic information is stored in nucleic acids, such as DNA and RNA, not proteins.
5. Step 5: Conclude that the most accurate statement regarding proteins is that they serve as enzymes, structural components, and signaling molecules in cells. This reflects their diverse and essential roles in biological systems.