1. Chapter 5- Enzymes

2. State Standard
Standard 1.b. – Enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings *

3. Enzymes Speed Up Chemical Reactions
Most of the essential chemical reactions in cells must occur quickly and precisely for the cell to survive
For a chemical reaction to begin, reactants must absorb some energy
- This energy is called the energy of activation (EA)

4. Enzymes Speed Up Chemical Reactions
Enzymes decrease the energy of activation

5. Enzymes Speed Up Chemical Reactions
EA without enzyme
EA with enzyme
Reactants
Net change in energy
Products
Figure 5.5B

6. Characteristics of Enzymes
Are proteins
Act as a biological catalyst
- Increase the rate of a reaction without being changed into a different molecule
Increase the rate of a chemical reaction by lowering the amount of energy of activation needed
Are not changed or used up in the chemical reaction
Are specific

7. Lecture Review
1. Which of the following can be used to start (initiate) a chemical reaction?
A. Addition of ATP
B. Heat and addition of
ATP
C. Enzymes
D. Heat
E. Heat and enzymes
2. True or False? Enzymes raise the activation energy to break the bonds of reactant molecules.
3. Most of a cell’s enzymes
are
A. Lipids
B. Proteins
C. Amino acids
D. Nucleic acids B
False

8. Lecture Review
4. The amount of energy that reactants need to start a chemical reaction is the _______.
5. When an enzyme catalyzes (speeds up) a chemical reaction
A. It acts as a reactant
B. It acts as a product
C. It raises the activation energy of a reaction
D. It lowers the activation energy of a reaction
4. Energy of Activation
5. D.

9. Enzymes Are Specific
Substrate – the substance the enzyme acts on, the reactant in a chemical reaction
Active site – the part of the enzyme molecule that binds to a substrate
Substrate
Active
site

10. Enzymes Are Specific Enzymes are specific
It takes many different kinds of enzymes to catalyze all the reactions of the cell
They have a unique 3D shape
The active site of an enzyme recognizes only the substrate(s) of the reaction it catalyzes

11. Enzymes Are Specific The active site
An enzyme is specific because the active site fits only the substrate(s) of the chemical reaction it catalyzes
The active site
Is a small part of the enzyme molecules that binds to the substrate
Is usually a pocket or groove on the surface of the enzyme
Forms temporary bonds with the substrate
Substrate
Active site

12. Lecture Review
1. Which of the following is not true of enzymes? A. Are proteins B. Act as a biological catalyst C. Supplies energy to start a chemical reaction D. Is specific E. Lowers the energy of activation
2. An enzyme is specific, this means
A. It has a certain amino acid sequence
B. It is found only in a certain place
C. It speeds up a particular reaction
D. It occurs in only one type of cell C

13. Lecture Review 3. Enzyme(s) A. Function depends on its 3D shape
B. Are not specific
C. Are used up in chemical reactions
D. All of the above
4. Why can a single enzyme molecule act on thousands or millions of substrate molecules per second?
5. What is the relationship between the active site and the substrate?
3. A
4. Because at the end of assisting one reaction, the enzyme returns to its original shape so it can bind to the next substrate
5. Substrate (what goes into the chemical reaction) binds to the enzyme’s active site (a small grove or pocket where the substrate fits like a lock and key)

14. How An Enzyme Works Enzyme available with empty active site
Substrate bonds to
active site with
induced fit
The enzyme is
unchanged and
can repeat the
process
Products are
released
Substrate is
converted to products

15. How An Enzyme Works Induced Fit
The interaction between the active site and substrate(s) causes the enzyme to change slightly so the active site fits the substrate better
Analogy – baseball and glove

16. Lecture Review
In your own words explain how an enzyme works. Include the following:
substrate enzyme
active site
product
induced fit

17. Factors that Affect Enzyme Activity
Enzyme activity is influenced by
- temperature
- salt concentration
- pH

18. Factors that Affect Enzyme Activity
Temperature
The optimum temperature occurs when the rate of
Contact between the active site and substrate is
greatest. In humans this is between 35-40oC
Higher temperatures denature
the enzyme altering the
shape of the active site
As temperature increases the
rate of contact between the
substrate and active site
increases

19. Lecture Review
1. Why does heating interfere with the activity of an enzyme? A. It kills the enzyme. B. It changes the enzyme’s shape. C. It decreases the energy of the substrate molecules. D. It causes the enzyme to break up. E. It decreases the chance that the enzymes will meet a substrate molecule.
1.B

20. Factors That Affect Enzyme Activity
The optimal pH for most enzymes is in the range of pH 6-8
At low pH H+ ions interfere with bonds that maintain the enzyme’s shape
At high pH OH- ions interfere with the enzyme’s shape

21. If additional Acid is added…

22. Lecture Review
2. Low pH and extremely salty conditions affect enzyme activity because A. They cause the structure of the enzyme to change. B. The salt and hydrogen ions compete with the substrate for the active site. C. The salt and hydrogen ions are irreversible inhibitors. D. They reduce the number of collisions between the enzyme and substrate
2.A

23. Lecture Review
3. The pH at which most enzymes’ activity is the greatest is A. pH 3 B. pH 5 C. pH 9 D. pH 7
3. D

24. Factors that Affect Enzyme Function
Salt concentration
In extremely salty solutions the salt ions interfere with some of the chemical bonds that maintain the enzyme’s shape and the enzyme is denatured.
Na+
Cl-

25. Lecture Review
Food rots when microbes break down food molecules. Food preservation methods interfere with the enzyme activity of microbes and prevent them from surviving. 4. Explain how each of the following would interfere with enzyme activity -pickling (soaking in acetic acid) -salting -canning (heating)

26. Factors that Affect Enzyme Function
Cofactors and coenzymes
Many enzymes will not work unless they are accompanied by cofactors or coenzymes
Cofactor – nonprotein helper. Ex: zinc, iron
Coenzyme – cofactor that is an organic molecule. Ex: many vitamins

27. Lecture Review
5. Some enzymes involved in hydrolysis cannot function without the help of sodium ions. Sodium in this case functions as A. A substrate B. A cofactor C. An active site D. A noncompetitive inhibitor E. A coenzyme
5. B

28. Factors that Affect Enzyme Function
Inhibitors
A competitive inhibitor takes the place of a substrate in the active site and prevents the substrate from binding to the active site

29. Factors that Affect Enzyme Activity
A noncompetitive inhibitor alters an enzyme’s function by changing its shape. The active site can no longer bind to the substrate.

30. Factors that Affect Enzyme Activity
JUST ADDED- not in Outline!!!
Feedback regulation to maintain homeostasis
The product of the reaction catalyzed by an enzyme acts as a reversible inhibitor and regulates the reaction… this is called negative feedback
Ex: enzymes involved in the breakdown of sugars to provide the ENERGY to recycle ADP +P back to ATP are inhibited by ATP…prevents cells from “burning” more sugar than needed!
A=sugar
D=ATP

31. Factors that Affect Enzyme Function
Irreversible inhibitors form covalent bonds between the enzyme and the inhibitor
Ex: certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system
Reversible inhibitors form weak bonds between the inhibitor and the active site
Ex: penicillin, an antibiotic, inhibits an enzyme that bacteria use in making cell walls

32. Lecture Review
A farm worker accidentally was splashed with a powerful insecticide. A few minutes later, he went into convulsion, stopped breathing, and died. The insecticide was a competitive inhibitor of an enzyme important in the function of the nervous system. 6. Describe the relationship between the structure of the enzyme, the structure of its substrate, and the structure of the insecticide.

33. Factors that Affect Enzyme Function
Negative Feedback
The product of a reaction acts as a reversible inhibitor of the enzyme that catalyzes the reaction
This regulates the reaction