1. Topic 5: Enzymes Pg

2. What are enzymes?
enzymes are proteins that function as biological catalysts
a catalysts is a substance that usually speeds up the rate of a chemical reaction and is not changed by the reaction
thus enzymes speed up the rate of metabolic reactions in the cells

3. Enzymes work
enzymes lower the minimum amount of energy required for chemical reaction to occur (activation energy)
this allows biochemical reactions to take place at a faster rate in the cells of living organisms at body temperature which is usually low
enzymes catalyse metabolic reactions (i.e. chemical reactions that sustain life) in a cells
metabolic reactions are either breakdown reactions - catabolism or build up reactions - anabolism

4. Naming of Enzymes
Enzyme are named according to the reaction they catalyse
A suffix – ase is usually added to the name of the substrate of the reaction catalysed by the enzyme
Sometimes they are given special names such as catalase & amylase
Catalase is the fastest acting enzyme

5. How Enzymes Work

6. “Lock and Key” Model
Each enzyme has a shape that allows it to catalyse one reaction
Reactant(s) in an enzyme – catalysed reaction is/are called substrate(s)
Enzyme’s molecule has a specific shape which is complementary to that of a substrate –this is called active site
The substrate fits into the active site of the enzyme the same way a ‘key fits into a lock’ - this is called “ lock and key” model
The substrate (the ‘key’) fits exactly into the active site (the ‘key hole’) of the enzyme (the ‘lock’)
An enzyme-substrate complex is formed.
The substrate undergoes a chemical change – a new substance, the product, is formed
The product is released from the active site.
The free unaltered active site is ready to receive fresh substrate.

8. General Properties of Enzymes
enzymes are all Proteins
enzymes are Specific in reaction they catalyse
enzymes are not changed by the reaction they catalyse i.e. they can be used again and again
enzymes are influenced by change in temperature
enzymes are influenced by change in pH
enzymes work best at particular temperature (37 oC in humans)and pH (pH 2 for pepsin & pH 7 for most enzymes)

9. Factors Affecting Enzyme Activity
Enzyme activity is determined by measuring the rate of reaction that the enzyme catalyses
This is usually measured by measuring the products formed per unit time
Enzyme activity is affected by;
temperature,
pH &
substrate concentration

10. Effect of Temperature on Enzymes
at low temperature (e.g. 0°C) enzyme activity is low because the movement of molecules is slow due to low kinetic energy
the collision frequency between enzyme and substrate is therefore low
increasing the temperature, increases kinetic energy of molecules thus speeding up their movement, collision frequency between the substrates and the enzymes increases therefore enzyme activity increases
maximum enzyme activity is at 40°C – due to maximum collision frequency between enzymes and substrates molecules – this is called optimum temperature (i.e. the temperature at which the enzyme works fastest)
enzyme action decreases above 40°C because the enzymes are denatured by excess temperature (i.e. the shape of active site is altered & substrates molecules can no longer fit into it)
when all the enzymes are denatured, at 60°C, enzyme activity stops

11. Effect of pH on Enzymes
enzyme activity is greatest within a narrow range of pH, since all the enzymes are functioning normally because their active sites have the correct shape
this is called the optimum pH
change in pH from the optimum, alters the shape of active site thus affecting the ability of the substrates to bind to the active site & so enzyme activity decreases
a major change in pH from the optimum denatures the enzymes so enzyme action stops
What is the optimum pH for;
enzyme X?
enzyme Y?

12. Use of enzymes in: germination of seeds, biological washing products & food industry
Enzymes are widely used in industry because;
they work at lower temperature than other catalysts thus reducing cost of fuel
they are not destroyed by the reaction the catalyse, thus they can be used over and over again
Applications of enzymes in day – to – day life include;
Hydrolysis of stored food during seed germinations
Use of enzymes in food industry such as juice extraction, brewing industry to make beer
Making of biological washing powders
Producing antibiotic penicillin

13. Use of enzymes in: germination of seeds
enzymes in seeds breakdown stored food substance into soluble end products which can be translocated to growing regions
starch is broken down to maltose by the enzyme amylase
fats/oils are broken down by lipase to fatty acids and glycerol
maltose & fatty acids are respired to provide energy for germination

14. Production of apple juice
enzyme pectinase is added to crushed apple fruit pulp
the enzyme breaks down pectin in plant cell walls releasing more juice from the crushed apples

15. Use of enzymes in biological washing powders
presence of enzymes in biological washing powders increase the efficiency of the washing powder in removing stains from clothes because:
stains may be protein or fat which are not removable with detergent only
presence of lipase breaks down fat stain into fatty acids & glycerol
presence of protease breaks down protein stain into amino acids
fatty acids, glycerol & amino acids are soluble in water thus easily washed away

16. Controlling the temperature of the wash
temperature of the wash needs to be carefully controlled because:
high temperature denatures enzymes , so enzymes will not work
at low temperature, enzymes are inactive thus they work slowly
constant optimum temperature such as 37 oC maintains optimum conditions for enzyme activity

17. Use of microorganisms & industrial fermenters to manufacture the antibiotic
industrial fermenters are large metal tanks that uses microorganisms to produce useful products such as antibiotics such as penicillin
the organism involved, fungus Penicillium is added to the tank together with nutrients such as sugar & ammonium salts (or amino acids)
Penicillium produce enzymes which converts the substrate into penicillin, antibiotic used to cure bacterial infections
sugar provide energy for respiration while ammonium salt is used to produce proteins & nucleic acids

18. Maintaining suitable conditions in the industrial fermenters
suitable conditions such as optimum pH, optimum temperature and supply of oxygen & nutrients are required
air is bubbled through to provide oxygen for respiration
stirring using paddles keeps microorganism suspended so they always have access to nutrients & O2 and rolls the fungus into little pellets making it easy to separate liquid from the culture
water -cooled jacket maintains a constant temperature of 24 oC
probes monitor the temperature & pH in the tank. pH is maintained at 6.5 by adding alkalis where necessary
after 6 days, fermentation is complete & the mixture is drained & filtered
penicillin is then extracted

19. Role of the fungus Penicillium in the production of antibiotic penicillin
fungus penicillium produces enzymes that converts the substrate into penicillin, antibiotic used to cure bacterial infections

20. Revision activity
After reading pages of your biology textbook and your lesson notes, attempt Revision Questions on page 48.