1. Enzymes
Lesson 13

2. Success Criteria
State that enzymes are globular proteins with a specific tertiary structure
State that enzymes catalyse metabolic reactions
State that enzyme action may be extracellular or intracellular
Describe the mechanism of enzyme action
Explain what is meant by enzyme-substrate complex and enzyme-product complex
Describe how enzymes lower activation energy
Explain the importance of coenzymes and cofactors in enzyme controlled reactions

3. Starter Look at the two jellies, what has happened and why?
Think, pair, share

4. Key Information: Enzymes
Enzymes are globular proteins with a specific tertiary structure
Enzyme action may be intracellular or extracellular
Enzymes are biological catalysts
Enzymes catalyse metabolic reactions
Enzymes lower activation energy because of the way the active site is shaped to fit the substrate

5. GCSE Recap
Use the plasticene to model the lock and key model of enzyme action

6. Characteristics of Enzymes
They are proteins of high molecular weight
They are biological catalysts
They are sensitive to temperature changes being denatured at high temperatures
They are sensitive to pH
They are generally specific in the reactions they catalyse
Enzymes possess an active site within which chemical reactions take place
Substrate
molecule in
the ACTIVE
SITE
Enzyme molecule

7. The Active Site
Enzyme
molecule
Active
site
Reaction
occurs
Substrate
molecules
(complementary
shape to active
site)
Product
molecules
diffuse away
from the
active site
Enzyme substrate complexes form
Substrate molecules bind with enzyme molecules at the active
site as a consequence of their complementary shapes. This is the
basis of the LOCK AND KEY MODEL of enzyme activity

8. Task Read page 127 in the text book
Create a comparison table for lock and key and induced fit hypothesis
Lock and Key Model
Induced Fit Hypothesis

9. The Lock And Key Model
In an enzyme - catalysed reaction, the enzyme binds
to the substrate to form a complex
Enzyme
molecule
An enzyme - substrate complex
forms S
Products diffuse
away from the
active site
A reaction
occurs
forming an
enzyme - product
complex
The lock & key model
proposes that the substrate
binds to the active site
which it fits exactly, like a
key in a lock

10. The Induced Fit Model
This model takes into account the fact that proteins (enzymes)
have some three-dimensional flexibility
Substrate binds to the enzyme
at the active site
SUBSTRATE
Binding of the substrate
induces the enzyme to change
shape such that there is an
exact fit once the substrate
has bound
According to this model, reactions can
only take place AFTER induced fit has occurred
Enzyme Molecule

11. Key Terms Specificity, Active site, Lock and key hypothesis,
The active site of an enzyme is a specific shape, depending on the reaction that it catalyses, meaning that other molecules won’t fit into the active site
Active site,
The area on an enzyme to which the substrate binds
Lock and key hypothesis,
The theory of enzyme action in which the enzyme active site is complementary to the substrate molecule, like a lock and key
Induced-fit hypothesis,
The theory of enzyme action in which the enzyme molecule changes shape to fit the substrate molecule more closely as it binds to it
Enzyme-substrate complex,
The intermediary formed when a substrate molecule binds to an enzyme molecule
Enzyme-product complex
The intermediate structure in which product molecules are bound to an enzyme molecule lowering of activation energy

12. Task Answer the following question Use as many key terms as possible
Describe the mechanism of enzyme action
Use as many key terms as possible
Person with the most key terms used correctly wins a prize

13. Peer Assess Swap answers Highlight all the key terms in their response
Enzyme
Substrate
Enzyme substrate complex
Enzyme product complex
Product
Collision
Active site
Lock and key
Induced fit
Maximum mark of 9, lose a mark for every incorrectly used term or missed term

14. Cofactors and Coenzymes
Cofactor: substance that must be present for enzyme controlled reactions to take place at the appropriate rate
Prosthetic group: inorganic ion that is a permanent part of the enzyme contributing to its 3D shape
Coenzyme: organic molecule that binds either just before or at the same time as the substrate (help reactions take place in sequence)
Inorganic ions: either bind to enzyme or substrate to help form the enzyme substrate complex

15. Task
Role play, model or draw the effect of coenzymes and cofactors in enzyme controlled reactions

16. Success Criteria
State that enzymes are globular proteins with a specific tertiary structure
State that enzymes catalyse metabolic reactions
State that enzyme action may be extracellular or intracellular
Describe the mechanism of enzyme action
Explain what is meant by enzyme-substrate complex and enzyme-product complex
Describe how enzymes lower activation energy
Explain the importance of coenzymes and cofactors in enzyme controlled reactions

17. Plenary
One form of COPD develops because enzymes are released by phagocytes entering the alveoli. This enzyme action can break down elastin in the lining of the bronchioles and alveoli. Use the example of elastin breakdown to explain the induced-fit hypothesis of enzyme action [5]

18. Plenary Markscheme elastin is substrate
(elastin / substrate) binds to / fits into , active site ;
active site / enzyme / elastase / substrate / elastin, shape changes
idea of closer fit (between active site and substrate)
more bonds form (between substrate and active site)
forms enzyme-substrate-complex / ESC
idea that (change in shape of active site) destabilises / weakens , bonds (in substrate) / substrate
activation energy reduced
idea of further shape change of, active site / enzyme, after products form

19. Homework
Make a glossary of key enzyme terms