1. Enzyme
Grade 8 Year

2. What Are Enzymes? Enzymes are proteins.
Enzymes are catalysts that speed up chemical reactions
Each enzyme catalyses one reaction
They can be used again and again
They are influenced by temperature and pH.
proteins
catalyst

3. Kinds of Enzymes Enzyme Reaction Amylase
Breakdown starch (starch hydrolysis)
Catalase
Breakdown hydrogen peroxide (H2O2) to water and oxygen
Cellulase
Breakdown of cellulose in plant cell walls
Lactase
Hydrolysis of the milk sugar lactose
Lipases
Digestion of fats
Proteases
Digestion of protein

4. How Do Enzymes Work? Breaking large molecules into small ones
e.g. starch is broken down into glucose
Building up large molecules from small ones
e.g. glucose are joined together into cellulose
Converting one small molecule into another
e.g. remove hydrogen from compounds during respiration

5. ‘Lock and Key’ Model Enzymes work on substances called substrates.
The reaction takes place on a part of the surface of the enzyme called the active site.

6. Effects of Temperature on Enzymes

7. Optimum Temperature
The temperature at which the maximum rate of reaction occurs.
Examples:
Fungal and plant enzymes: 200 C
Human enzymes : 37 0 C
Some enzymes produced by bacteria : 900 C

8. Effects of pH on Enzymes
Many enzymes work best in neutral conditions, but some prefer acidic and some alkaline conditions

9. Questions Which of the following enzymes would digest a fat?
(a.) sucrase (b.) fatase (c.) protease (d.) lipase
At high temperatures, the rate of enzyme action decreases because the increased heat
(a.) changes the pH of the system
(b.) alters the active site of the enzyme
(c.) neutralizes the acids and bases in the system (d.) increases the concentration of the enzyme

10. An enzyme that hydrolyzes protein will not act upon starch
An enzyme that hydrolyzes protein will not act upon starch. This fact is an indication that enzymes are
(a.) hydrolytic (b.) specific
(c.) catalytic (d.) synthetic
Which chemical is classified as an enzyme?
(a.) galactose (b.) lipid
(c.) protease (d.) hydrogen peroxide
Here are of some stages of an enzyme-controlled reaction
An enzyme-substrate complex is represented by diagram  (1.) A  (2.) B  (3.) C  (4.) D

11. Which statement best expresses the information represented in the graph shown?
(a.)  The action of enzymes varies with pH. 
(b.) A pH of 7 provides the optimum environment for digestive enzymes 
(c.) Gastric juice is active at a pH extending from 0 to 12. 
(d.) Acids have a pH greater than 7.