A Level Biology Lesson 17:

Enzymes: The Models of Enzyme Actions. Lock and Key & Induced Fit.

Task 1. Check Where this Lesson fits into your Exam Specification!

Task 2. Watch the Revision Notes Lesson in Full.

00:00 Intro Screen

00:10 Learning Outcomes.

00:26 Enzymes are Specific...

01:00 The process of Enzyme action (easily summarised).

01:30 The specificity of the Enzyme substrate complex...

02:11 The Lock and Key Model of Enzyme Action...

02:58 Theories can change over time...

03:38 The Induced Fit Model of Enzyme Action...

05:03 Key points - Summary

Download, Print out & complete the accompanying A3 Poster


Check Your Spec!


★ AQA Specification Reference: - Many proteins are enzymes. The induced-fit model of enzyme action. The properties of an enzyme, structure of its active site and its ability to combine with complementary substrate(s) to form an enzyme-substrate complex. The specificity of enzymes. Students should be able to: appreciate how models of enzyme action have changed over time.


★ CIE Specification Reference: - 3 Enzymes: 3.1 Mode of action of enzymes. c) explain the mode of action of enzymes in terms of an active site, enzyme/substrate complex, enzyme specificity (the lock and key hypothesis and the induced fi t hypothesis should be included).


★ Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 2: Genes and Health - 2.10 i) Understand the mechanism of action and the specificity of enzymes in terms of their three-dimensional structure.


★ Edexcel (Biology B) Specification Reference: - Topic 1: Biological Molecules. 1.5 Enzymes – i) Know the structure of enzymes as globular proteins. ii) Understand the concepts of specificity and the induced fit hypothesis.


★ OCR (Biology A) Specification Reference: - Module 2 – Foundations in biology. 2.1.4 Enzymes. (c) the mechanism of enzyme action - active site, lock and key hypothesis, induced-fit hypothesis, enzyme-substrate complex.


★ OCR (Biology B) Specification Reference: - Module 2 – Cells, chemicals for life, transport and gas exchange. 2.1.3 Proteins and enzymes. (c) how the structure of globular proteins enable enzyme molecules to catalyse specific metabolic reactions. Specificity of the active site, the formation of enzyme substrate complexes.


★ WJEC Specification Reference: - UNIT 1: Basic Biochemistry and Cell Organisation Remember Specifications are often very vague - No matter which exam board you are studying you need to know this. (d) active sites, interpreted in terms of three dimensional structure (e) the theory of induced fit.


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