1. Chapter 5: Enzymes

2. Enzymes are Biological Catalysts
What are enzymes?
Biological catalysts made up of protein which alter rate of chemical reaction without themselves being
chemically changed at the end of reactions
Catalysts : Substance that increase rate of reaction without being used up.

3. Enzymes are Biological Catalysts
Enzymes are made up of protein
Denatures (enzyme loses it shape and function) if exposed to high temperature or extreme changes in pH
Speeds up reaction without the need to increase temperature.

4. Mode of actions of enzymes
Breaking down of fats
Heat at high temperature
Using enzymes
Body cannot withstand high temperatures
Energy is required to start breaking down fats – activation energy
Enzymes lower activation energy > Required to start chemical reaction.

5. Enzymes-catalysed Reactions
Digestion
Process whereby large insoluble food substances are broken down into small soluble molecules
Carbohydrates  Monosaccharides
Protein  Amino Acids
Fats  Fatty Acids + Glycerol

6. Enzymes-catalysed Reactions
2. Synthesis of complex substances from simpler ones.
Synthesis of proteins
Synthesis of glycogen for storage in the body
Synthesis of fats

7. Enzymes-catalysed Reactions
3. Oxidation of Glucose
Release of Energy to do work
Involves a series of enzyme catalysed reactions
4. Breakdown of toxic materials
Hydrogen peroxide to water and oxygen catalysed by catalase.
Enzymes catalyse almost all reactions in body.
There are many different types of enzymes and each
is specific and will be produced only when required.

8. Classifying Enzyme According to chemical reaction they catalyse
Usually ends up with –ase
Example:
Breaking down of starch = amylase
Breaking down of Protein = Protease
Breaking down of Lipids/Fats = Lipase
Enzyme combine with molecules it acts upon (substrate) to form an enzyme-substrate complex.
Enzyme controlled reaction can be either
Anabolic : building up larger molecules
Catabolic: breaking down large molecules into smaller molecule

9. Characteristics of Enzymes
Speeds up rate of chemical reactions
Required in minute amount (small) – (itself not breakdown)
Specific (Lock & Key hypothesis)

10. Lock & Key Hypothesis
Substrate which the enzyme acts on is called substrate
Example: Breaking down of starch, amylase is the enzyme and starch is substrate. End-product = Maltose
Enzyme molecules are usually larger than substrate
Small part of enzyme, called active site comes into contact with substrate
Enzyme (lock) and substrate(key)
Enzyme(lock)
Substrate (Key)
Product
Amylase
Starch
Maltose
Lipase
Lipid
Fatty acids + glycerol
Protease
Protein
Amino acids

11. Active site
Enzyme substrate complex
amylase
starch
2 maltose units
amylase

12. Enzyme are affected by temperature
Enzyme and substrate in constant motion
Increase temperature results in increased kinetic energy
Molecules move faster
Rate of enzyme colliding with substrate is higher
Rate of enzyme-substrate complex formed higher
Only up to an optimum temperature
Low temperature = enzymes are inactive

13. Enzyme are affected by temperature
Around 37 ℃ in mammals
Too high a temperature will result in protein being denatured
Active sites change shape and activity gradually decline
Different enzymes can withstand different temperature range
Most enzymes will be completely denatured above 60 ℃
Molecules move slower and rate of collision lower

14. Q: How does temperature affect Enzyme activity
What happens at low temperature?
Enzyme are inactive at low temperature
What happens as temperature increase?
As temperature increase, enzymes gain more kinetic energy causing them to move faster. When they move faster, chances of colliding into a substrate is higher. Hence, rate of forming enzyme-substrate complex is higher. Rate of reaction increases
What happens at optimum temperature?
At optimum temperature, enzyme are most active
What happens above optimum temperature?
Enzymes loses active sites, denatured.

15. Enzymes are affected by temperature:
Activeness of enzymes
0 ℃
50 ℃
100 ℃

16. Enzyme are affected by pH
Enzyme usually work efficiently within a narrow pH range.
Some enzymes works best in slightly acidic conditions (pepsin and rennin) while others in slightly alkaline conditions.
Extreme pH will result in denaturation of enzymes
Low
High
Temperature
Inactive
Denatured
pH value
denatured

17. Enzymes are affected by pH:
Activeness of enzymes
pH 1
pH 7
pH 14

18. Enzyme are affected by Enzyme concentration
Increase enzyme concentration, increased rate of reaction
Temperature and pH are at optimum values
Substrate level must be high.

19. Enzyme are affected by substrate concentration
Concentration of enzyme remains the same
Increased substrate concentration doesn’t necessarily increase rate of reaction
Active sites become saturated, therefore could not work any faster

20. For example, you are making burgers with buns
and the number of patties you have is limited.
Buns = Substrate, Patties = Rate of reaction 5
No. of patties
(Rate of
Reaction) 4 3 2 1
Number of buns
(substrate) 2 4 6 8 10

21. Enzyme are affected by substrate concentration
How do you know that substance is not enough?
When I increase number of substance, I can produce more burgers (Also: When I increase number of that substance, there is an increase of rate of reaction)

22. Limiting Factors
Any factor that directly affects the rate of reaction if its quantity is changed
Value of this factor has to be increased in order to increase rate of reaction

23. D C A B Reversible Reactions
Most reactions in living cells are reversible.
Enzyme can catalyse reversible reactions
Usually not allowed as products formed are used up or transported away.
REACTANTS    PRODUCTS D C B A
PRODUCTS     REACTANTS