When a protein is denatured, which of the following best describes what happens to its structure?

• A. Its secondary and tertiary structures are disrupted, but the primary structure remains intact.
• B. Its primary structure is broken down into individual amino acids.
• C. It becomes more catalytically active.
• D. It gains additional quaternary structure.

Answer: (A)

Verified step by step guidance

1. Understand the concept of protein structure: Proteins have four levels of structure—primary, secondary, tertiary, and quaternary. The primary structure refers to the sequence of amino acids, while secondary, tertiary, and quaternary structures involve folding and interactions between amino acids.
2. Define denaturation: Denaturation is a process where a protein loses its functional shape due to external factors like heat, pH changes, or chemicals. This process disrupts the secondary and tertiary structures but does not break the covalent bonds in the primary structure.
3. Analyze the options: Evaluate each option based on the definition of denaturation. For example, the primary structure remains intact during denaturation, so any option suggesting its breakdown is incorrect.
4. Focus on the correct description: Denaturation disrupts the secondary and tertiary structures, which are responsible for the protein's functional shape. It does not make the protein more catalytically active or add quaternary structure.
5. Conclude: The correct answer is the option stating that the secondary and tertiary structures are disrupted, but the primary structure remains intact. This aligns with the biochemical understanding of denaturation.