1. YEAR 12 - AS Biology 29th November 2005
Enzymes
dr shabeel pn

2. Lesson Objectives Enzyme unit overview What are they? How they work
Activation energy
What controls their activity
Rates of reaction
Substrate/enzyme concentrations
Temperature, pH
Enzyme inhibitors
Practical to demonstrate “Catalase” activity in different tissue samples

3. Previous related topics covered?
Enzyme controlled reactions?
Proteins?
Lipase, protease, pectinase, amylase etc?
“Lock & Key” molecular structures?

4. By the end of the unit you should be able to:-
Explain enzymes as Globular Proteins which act as catalysts
Explain their catalytic action in terms of lowering activation energy
Describe examples of enzyme-catalysed reactions
Discuss factors affecting reaction rates and inhibition
Describe how to investigate these effects experimentally

5. Enzymes:- Usually end in ‘…ase’.
Are defined as a BIOLOGICAL catalyst i.e. something that speeds up a reaction. Up to 1012 fold
Usually end in ‘…ase’.
Discovered in 1900 in yeasts. Some 40,000 in human cells
Control almost every metabolic reaction in living organisms
Are globular proteins coiled into a very precise 3-dimentional shape with hydrophilic side chains making them soluble
Possess an active site such as a cleft in the molecule onto which other substrate molecules can bind to form an enzyme-substrate complex
Once the substrate has been either synthesised or split, enzymes can be re-used.
Do not ‘create’ reactions
Widely used in industrial cleaning
Often require co-factors (co-enzymes) to function – metal ions, or vitamin derivatives

7. Amylase + starch substrate

8. How do enzymes work? Reaction Mechanism
In any chemical reaction a substrate is converted into a product.
In an enzyme catalysed reaction the substrate first binds to the active site of the enzyme to form the enzyme-substrate complex

10. Molecule Geometry
Substrate molecule fits into the enzyme like a lock & key.
Enzyme shape distorts or it changes other factors to make the reaction happen

11. “Activation Energy”
In a ‘natural’ reaction the product has a lower energy than the substrate so equilibrium will take it in the direction of the product.
However there is an energy ‘barrier’ to be overcome
Enzymes lower the activation energy required to bring about a reaction.
EG catalase reduces the activation energy for the reduction of H fold

13. Reaction rate factors Substrate concentration
Initially rate increases with substrate conc.