1. Endergonic and Exergonic Reactions
Endergonic reaction: requires energy, usually ATP
Exergonic reaction: releases energy, occurs spontaneously
energy
products + +
∆G > 0
reactants +
reactants
products
energy
∆G < 0

2. If exergonic reactions occur spontaneously, why isn’t the paper in front of you on fire?
An exergonic reaction

3. Just as the person may need a push to get started down a hill, many of the exergonic reactions that living organisms depend on for survival may need a “push”.
∆G < 0

4. Figure 6.12 Energy profile of an exergonic reaction
EA = activation energy

5. Example of an enzyme-catalyzed reaction: Hydrolysis of sucrose
energy +

6. In living organisms the “somethings” that provide that push are called enzymes
Without enzyme:
With enzyme:

7. Figure 6.13 Enzymes lower the barrier of activation energy

8. Most enzymes are protein molecules with a specific 3-dimensional shape
Active site
substrate
There are over 5000 enzymes known to exist, each of which is specific to a different reaction. Nearly every chemical process that takes place in living organisms is facilitated by an enzyme.
enzyme
“induced fit”

9. Enzymes catalyze reactions in living organisms:. 1
Enzymes catalyze reactions in living organisms: Bring reactant molecules close together 2. Make bonds easier to break/form

10. Notes about enzymes
Enzymes only increase the rate of exergonic reactions, they can’t cause non-spontaneous reactions to occur
Only the substrate will be altered, the enzyme will be released to work again
Enzymes are one type of catalyst

11. What determines how well an enzyme works?
Binding of enzyme and substrate
Temperature at which the enzyme functions

12. Can a species’ enzymes be shaped by natural selection?
Does the same enzyme show variation from one individual to another?
Is the form of enzyme an individual produce a heritable trait?
Does the form of enzyme individual produce affect its survival/reproduction?

13. Figure 6.16 Environmental factors affecting enzyme activity