1. Topic Three
Enzymes

2. Catalysts and Enzymes Why are enzymes important?
hundreds of chemical reactions are in progress in a typical living cell at a given moment
These reactions provide energy and substances needed for growth and repair
Chemical reactions would not be possible without ENZYMES

3. Watch a catalyst in action!
Catalysts
Catalyst = a chemical that speeds up the rate of a chemical reaction
Is not used up in the reaction
Watch a catalyst in action!

4. Enzymes are everywhere!
Enzyme = an organic catalyst
Made up of proteins
Allow chemical reactions to happen at room temperature
Speed up reactions without increasing temperature!
Enzymes are everywhere!
In saliva…
… stomach
… even mitochondria!

5. Draw the picture below to show how an enzyme works:
Substrate
Products
Active Sites
Enzyme-Substrate Complex
Enzyme
What type of reaction is this?
Hydrolysis or catabolic reaction.

6. Why are enzymes necessary?
Chemical reactions normally occur very SLOWLY!
Increasing temperature increases the rate of reaction
But increasing temperature too much will denature proteins and damage our cells!
Enzymes speed up the rate of a reaction without increasing the temperature

7. Activation Energy
Chemical reactions require an initial energy input to start
Ex: Rock must be rolled up the hill before it is able to roll down the other side of the hill by itself
Activation Energy = energy required to initiate (start) a chemical reaction

8. Enzymes do not change the amount of energy available!
Activation Energy
No enzyme = higher activation energy
With enzyme =
lower activation energy
Enzymes do not change the amount of energy available!

9. 3-2 Enzymes are Substrate Specific
Substrate: a molecule which attaches to the active site of an enzyme
Active site: Area of an enzyme that combines with a substrate molecule
Each enzyme is specific for a particular substrate
- Like lock and key

10. Substrates
Active Site

11. Naming of enzymes
Enzymes are given unique names based on the specific substrates
Enzyme name = name of the substrate + ASE
Sucrase
Sucrose + H2O
Fructose + Glucose

12. Naming Enzymes: Fill in the following table!!
Substrate
Enzyme
Maltose
Lactose
Protein
Starch
Lipids
Polypeptides
“ase”!
Maltase
Lactase
Protease
Not all enzymes end
with “ase”!! Pepsin
and Trypsin are
protein enzymes
that do not end
in “ase”
Amylase
Lipase
Peptidase

13. Not all enzymes end with “ase”
Not all enzymes end with “ase”!! Pepsin and Trypsin are protein enzymes that do not end in “ase.”
stomach
pancreas

14. 3-3 Basic Mechanism of Enzyme Action
Chemical reactions occur when molecules collide or bonds are broken
Enzymes increase the probability of reactions occurring inside cells by bringing substrate molecules CLOSER together
Enzymes can form bonds between molecules or break bonds

15. Lock and Key Hypothesis
The active site of the enzymes fits the substrate molecules
This forms an enzyme substrate complex
Product

16. Enzyme – Lock and Key HypothesisB B D F
A: substrates
B: enzyme
C: active site
D: enzyme-substrate complex
E: products
F: enzyme to be used again

17. 3-4 Coenzymes and Cofactors
Recall:
Cofactors are inorganic molecules
Examples: iron, zinc, calcium, magnesium and potassium
Coenzymes are organic molecules such as vitamins

18. Enzymes may not act alone...
Sometimes additional chemicals are necessary ingredients to permit enzyme activity
Enzyme co-factors and co-enzymes are often linked with enzyme activity
Coenzymes and cofactors change the shape of the active site on the enzyme!
Where a co-enzyme is lacking, enzyme activity may be reduced

19. Enzyme Action
2. Co-enzyme
3. Substrate
4. Products
1. Enzyme

20. Coenzymes and Cofactors
What happens when someone has a poor diet???
The chemical reactions requiring coenzymes (vitamins) and cofactors (minerals) cannot work when someone has a poor diet!!

21. Other factors affecting Enzyme Activity a) Temperature
Enzymes have an optimum temperature where the greatest number of molecular collisions occurs
An increase in temperature causes an increase in reaction rate
More molecules = more collisions
Optimum temperature range of most human enzymes is 35-40oC
Examples of optimum temperatures:
Hot springs bacteria = 85oC
Antarctic ice fish = 2oC

22. highest rate of chemical reactions
Temperature cont…
High temperatures cause enzymes to denature (change shape)
Why do you think high fevers for long periods of time are dangerous?
Optimal temperature =
highest rate of chemical reactions
Reaction
rate
Enzyme denatures
37oC
Temperature

23. Effects of pH
Optimal pH for most enzymes is pH 6-8 but some operate at more extremes
The enzyme pepsin has a optimal pH of 2
A pH above or below the optimal pH may cause denaturation
Enzyme activity will lower because the shape of the enzyme has changed…

24. Effects of pH

25. Substrate Concentration
As substrate concentration increases, enzyme activity increases
As enzyme active sites become full, if the number of substrate molecules exceed the number of enzymes molecules, then the reaction levels off.
No more enzymes available =
reaction rate leveling off
Reaction
rate
More substrate for the enzyme
to use = increasing reaction rate
Substrate concentration

26. Competitive Inhibitors
Inhibitors have shapes very similar to the substrate and also bind to the active site of the enzyme
When an inhibitor combines with the enzyme it prevents it from functioning properly
Inhibitor must be removed for normal functioning to occur
decreases enzyme activity by filling the active site so substrates cannot join!

27. Examples of competitive inhibitors include carbon monoxide, cyanide and penicillin

28. Carbon Monoxide (CO)
Many poisons and drugs act as competitive inhibitors…
CO for example competes with oxygen for the active site on the hemoglobin molecule.
In fact, it binds to hemoglobin 200X faster than oxygen! Once CO fits itself in, it rarely is dislodged

29. Cyanide
Cyanide attaches to enzyme in mitochondria, preventing the breakdown of sugars for energy. Cell dies!!
Without the energy needed for active transport, protein synthesis, transport of nutrients, and elimination of wastes, a cell dies almost instantly!

30. Penicillin Penicillin kills invading bacteria
Blocks an enzyme necessary for the synthesis of protective walls in bacteria
No effect on human enzymes

31. Topic 3-6: Control of Enzyme Activity
Many substances in the cell are produced by a metabolic pathway (a series of many chemical reactions involving enzymes)
Feedback inhibition = High levels of a substance will result in a decrease in its production