2.4 Enzymes
Chemical Reactions
Changes or transforms one set of substances into another
• Breaking and Reforming Bonds
• Example: O2 + 2 H2+ energy  2 H2O
Reactants
Products
Some release energy (exothermic)
Some absorb energy (endothermic)
All Chemical Reactions….
Require some energy to get things going (to start breaking bonds)
Activation Energy
The energy needed to get a reaction started.
Some chemical reactions often occur spontaneously. Others that
absorb energy cannot occur without a source of energy.

Role of Catalysts
• Allow reaction to happen more readily
• Speeds up the rate of the reaction
• NOT used up in the reaction
Enzymes
Proteins that speed up chemical reactions within
cells.
Example: carbonic anhydrase
CO2 + H2O  H2CO3
Converts Carbon Dioxide to Carbonic Acid 10 million
times faster than on its own by LOWERING THE
ACTIVATION ENERGY NEEDED to complete the reaction
How Enzymes Work?
Brings reactants close together (in correct orientation) so
reaction occurs much easier.
Active Site
is where
the
substrate
bonds to
the enzyme
Regulation of Enzyme Activity
The following affect the activity of enzymes:
1. Temperature
• What do you expect the ideal temperature of activity to be?
 (37 degrees Celsius – normal body temperature)
2. pH
• What effect would pH have on activity? Denature
• What pH would you expect stomach enzymes (peptidase,
lipase) to work most effectively at? – Acidic
3. Regulatory Molecules
• Bind to enzymes to speed up or slow down their activity by
turning them on or off.
Minute Paper

 On a separate piece of paper do your best to answer
the question (drawings work well!):
What role do enzymes play in living things?