Why are proteins considered polymers but not lipids?

• A. Proteins are hydrophilic, whereas lipids are hydrophobic.
• B. Proteins are synthesized in the ribosome, whereas lipids are synthesized in the mitochondria.
• C. Proteins are made of repeating amino acid units, while lipids are not composed of repeating monomeric units.
• D. Proteins contain peptide bonds, while lipids contain ester bonds.

Answer: (C)

Verified step by step guidance

1. Understand the definition of a polymer: A polymer is a large molecule composed of repeating structural units, typically connected by covalent chemical bonds.
2. Identify the structure of proteins: Proteins are composed of amino acids linked together in a chain by peptide bonds. Each amino acid is a monomer, and the chain of amino acids forms a polymer.
3. Examine the structure of lipids: Lipids are not composed of repeating monomeric units. They are typically made up of a glycerol backbone bonded to fatty acids, but these components do not repeat in a chain-like structure.
4. Compare the bonding in proteins and lipids: Proteins contain peptide bonds between amino acids, while lipids contain ester bonds between glycerol and fatty acids. This difference in bonding reflects their structural differences.
5. Conclude why proteins are considered polymers: Since proteins are made of repeating amino acid units, they fit the definition of a polymer. In contrast, lipids do not have a repeating monomeric structure, so they are not classified as polymers.