1. Chapter 5
The Working Cell

2. HOW ENZYMES FUNCTION
5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers

3. For a chemical reaction to begin
Reactants must absorb some energy, called the energy of activation
EA barrier
Reactants
Products 1 2
Enzyme
Figure 5.5A

4. Progress of the reaction
A protein catalyst called an enzyme
Can decrease the energy of activation needed to begin a reaction
Reactants
EA without enzyme
EA with enzyme
Net change in energy
Products
Energy
Progress of the reaction
Figure 5.5B

5. 5.6 A specific enzyme catalyzes each cellular reaction
Enzymes have unique three-dimensional shapes
That determine which chemical reactions occur in a cell

6. The catalytic cycle of an enzyme1
Enzyme available with empty active site
Active site
Substrate (sucrose) 2
Substrate binds to enzyme with induced fit
Enzyme (sucrase)
Glucose
Fructose
H2O 4
Products are released 3
Substrate is converted to products
Figure 5.6

7. 5.7 The cellular environment affects enzyme activity
Temperature, salt concentration, and pH influence enzyme activity
Some enzymes require nonprotein cofactors
Such as metal ions or organic molecules called coenzymes

8. 5.8 Enzyme inhibitors block enzyme action
Inhibitors interfere with an enzyme’s activity

9. Normal binding of substrate
A competitive inhibitor
Takes the place of a substrate in the active site
A noncompetitive inhibitor
Alters an enzyme’s function by changing its shape
Substrate
Enzyme
Active site
Normal binding of substrate
Enzyme inhibition
Noncompetitive inhibitor
Competitive inhibitor
Figure 5.8

10. CONNECTION
5.9 Many poisons, pesticides, and drugs are enzyme inhibitors