Advanced Placement (AP) Biology Practice Exam

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What is one characteristic that distinguishes lipids from true polymers?

Size of the molecules
Presence of ester bonds
Structure of being a continuous chain
They do not consist of repeating subunits

The correct answer is: They do not consist of repeating subunits

Lipids are distinguished from true polymers primarily due to their lack of a consistent structure formed by repeating subunits. True polymers, such as proteins, nucleic acids, and carbohydrates, are composed of many smaller, identical or similar units (monomers) that are covalently bonded in a chain-like fashion, resulting in a large molecule with a well-defined, repetitive structure. In contrast, lipids, such as triglycerides, phospholipids, and steroids, do not have this repetitive chain structure. Instead, they are typically formed from a variety of smaller components, and their assembly is not characterized by the repetition of a single type of monomer. For example, a triglyceride consists of glycerol and three fatty acid chains, which do not repeat across the molecule. This distinction is significant because it reflects the diverse functions and properties of lipids compared to true polymers, reinforcing their unique roles in biological systems, such as energy storage, membrane formation, and signaling.