A Levels Biology (9700)•9700/12/O/N/22

Explanation
Active site formation in tertiary structure
Steps:
- Identify that globular proteins like enzymes catalyze reactions via their tertiary structure's 3D shape.
- Recognize the active site as a pocket where substrate binds, formed by specific amino acid R groups.
- Eliminate options not directly enabling catalysis: A misstates hydrophobic positioning; C confuses denaturation; D describes a structural feature but not the catalytic property.
- Confirm B as the key interaction for substrate binding and reaction facilitation.
Why B is correct:
- The tertiary structure positions R groups to form the active site, allowing specific bonds with substrate for catalysis, per enzyme-substrate complex theory.
Why the others are wrong:
- A: Hydrophobic R groups are typically inside the protein, not outside, to stabilize the core in aqueous environments.
- C: High temperatures denature proteins, disrupting structure, not donating properties.
- D: Hydrogen bonding maintains overall shape but does not directly enable substrate interaction.
Final answer: B
Topic: Mode of action of enzymes
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