1. Protein Functions 5.3,

2. 5.3 Chemical reactions either store or release energy
Endergonic reactions
Require an input of energy from the surroundings
Yield products rich in potential energy
Energy is ABSORBED
Example: photosynthesis

3. Amount of energy required
LE 5-3a
Products
Amount of
energy
required
Energy required
Potential energy of molecules
Reactants

4. Exergonic reactions Release energy
Yield products that contain less potential energy than their reactants
Examples: cellular respiration, wood burning

5. Amount of energy released
LE 5-3b
Reactants
Amount of
energy
released
Energy released
Potential energy of molecules
Products

6. Cells carry out thousands of chemical reactions, which constitute cellular metabolism
Energy coupling uses energy released from exergonic reactions to drive endergonic reactions

7. HOW ENZYMES FUNCTION
5.5 Enzymes (types of proteins) speed up the cell's chemical reactions by lowering energy barriers
Energy of activation
Amount of energy that must be input before an exergonic reaction will proceed (the energy barrier)

9. Enzymes Proteins that function as biological catalysts
Increase the rate of a reaction without themselves being changed
An enzyme can decrease the energy of activation needed to begin a reaction

10. LE 5-5b enzyme enzyme EA without EA with Reactants Energy Net change
in energy
Products
Progress of the reaction

11. 5.6 A specific enzyme catalyzes each cellular reaction
Each enzyme has a unique three-dimensional shape that determines which chemical reaction it catalyzes
Substrate: a specific reactant that an enzyme acts on
Active site: A pocket on the enzyme surface that the substrate fits into

12. Animation: How Enzymes Work
Induced fit: The way the active site changes shape to "embrace" the substrate
A single enzyme may act on thousands or millions of substrate molecules per second
Animation: How Enzymes Work

13. LE 5-6 Enzyme available with empty active site Active site Substrate
(sucrose)
Substrate binds
to enzyme with
induced fit
Enzyme
(sucrase)
Glucose
Fructose
H2O
Products are
released
Substrate is
converted to
products

14. 5.7 The cellular environment affects enzyme activity
Physical factors influence enzyme activity
Temperature, salt concentration, pH
Some enzymes require nonprotein cofactors
Metal ions, organic molecules called coenzymes

15. 5.8 Enzyme inhibitors block enzyme action
Inhibitors interfere with an enzyme's activity
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
In feedback inhibition, enzyme activity is blocked by a product of the reaction catalyzed by the enzyme

16. Normal binding of substrate
LE 5-8
Substrate
Active site
Enzyme
Normal binding of substrate
Competitive
inhibitor
Noncompetitive
inhibitor
Enzyme inhibition

17. CONNECTION
5.9 Many poisons, pesticides, and drugs are enzyme inhibitors
Cyanide inhibits an enzyme involved with ATP production during cellular respiration
Some pesticides irreversibly inhibit an enzyme crucial for insect muscle function
Many antibiotics inhibit enzymes essential for disease-causing bacteria
Ibuprofen and aspirin inhibit enzymes involved in inducing pain