College Board-Aligned Original Notes

AP Biology Unit 3 Topic 1: The structure and function of enzymes

Enzymes speed biological reactions by lowering activation energy while their shape and conditions control activity.

Unit 3: Cellular Energetics. College Board exam weighting listed for this unit: 12%-16% of exam score.

What to Know

Enzymes bind specific substrates at active sites and stabilize the transition state.
Temperature, pH, salt concentration, inhibitors, and activators can change enzyme activity.
Enzymes are not consumed by the reactions they catalyze, so they can be reused.
Always connect this topic back to the larger unit: Cellular Energetics.

Detailed Notes

The structure and function of enzymes belongs to Unit 3: Cellular Energetics. Enzymes speed biological reactions by lowering activation energy while their shape and conditions control activity. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Enzymes bind specific substrates at active sites and stabilize the transition state. Temperature, pH, salt concentration, inhibitors, and activators can change enzyme activity. Enzymes are not consumed by the reactions they catalyze, so they can be reused.

Model to use: Use an energy diagram to compare a reaction with and without an enzyme and label the activation energy change. A clear model should label the parts, show the direction of movement or information flow when relevant, and connect the diagram back to the biological outcome.

AP-style move: In lab-style questions, interpret reaction rate patterns and connect them to enzyme shape, substrate concentration, or inhibition. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.

Key Vocabulary

Active site

The region of an enzyme where the substrate binds and the reaction occurs.

Substrate

A reactant that binds to an enzyme.

Activation energy

The energy required to start a chemical reaction.

Induced fit

A change in enzyme shape that improves fit with the substrate.

Competitive inhibitor

A molecule that blocks the active site by competing with the substrate.

Allosteric regulation

Control of protein activity through binding at a site other than the active site.

Quick Practice

How would you explain The structure and function of enzymes in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

Biology concept reference: Biology for AP Courses by OpenStax, Rice University. Access for free at OpenStax. Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. EduCompanion used this source as a conceptual reference and rewrote the study notes in original wording.