Enzymes

What Enzymes covers

Enzymes is the fourth section of Module 2. It covers what an enzyme does to the activation energy of a reaction, the lock and key and induced fit models of the active site, the conditions that raise and lower activity, and the cofactors, coenzymes and inhibitors that change how an enzyme works.

The 3 subtopics

Each one has its own page.

• Enzyme action: lock and key and induced fitIntracellular and extracellular enzymes, what determines specificity, the active site and the two models of how a substrate binds, and the lowering of activation energy.Open →
• Factors affecting enzyme activityHow temperature, pH, enzyme concentration and substrate concentration change the rate, the temperature coefficient Q10, and why serial dilutions are used.Open →
• Cofactors, coenzymes and enzyme inhibitionCofactors and coenzymes and where they come from, competitive and non-competitive inhibitors, reversible and non-reversible inhibition, and end-product inhibition.Open →

What you need to know

Answer each one before you reveal it.

Take Enzymes further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Competitive inhibitor vs Non-competitive inhibitor

  Competitive inhibitor: a molecule that binds the active site and blocks the substrate. Non-competitive inhibitor: a molecule that binds elsewhere and changes the shape of the active site.

• Induced fit model vs Lock and key model

  Induced fit model: the active site moulds around the substrate as it binds. Lock and key model: the active site is already exactly complementary to the substrate.

• Cofactor vs Coenzyme

  Cofactor: a non-protein component an enzyme needs to work. Coenzyme: an organic non-protein molecule that is required for some enzymes to function.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What are enzymes and at what levels do they control reactions?

   Model answer

   Enzymes are biological catalysts that control metabolic reactions at both cellular and whole organism levels.

2. 2

   How do enzymes influence organisms beyond just catalysing reactions?

   Model answer

   Enzymes affect both the structure and function of organisms.

3. 3

   Define intracellular enzymes.

   Model answer

   Intracellular enzymes are enzymes that catalyse reactions inside cells.

4. 4

   Define extracellular enzymes.

   Model answer

   Extracellular enzymes are enzymes that catalyse reactions outside cells.

5. 5

   Name an enzyme that catalyses intracellular reactions.

   Model answer

   Catalase.

6. 6

   Give an example of an enzyme that functions extracellularly.

   Model answer

   Amylase.

What is inside Levo

Six ways to work the same material.

Enzymes revision questions

What does Enzymes cover in OCR A-Level Biology?

3 subtopics: enzyme action: lock and key and induced fit, factors affecting enzyme activity and cofactors, coenzymes and enzyme inhibition. Each one has its own page with questions and model answers.

How is Enzymes organised?

By the OCR H420 specification, subtopic by subtopic, so it matches the order you are taught it in.