1. Enzymes Promote Chemical Reactions
Catalysts for biological reactions (speed up chemical reactions in cells)
Most are proteins built of amino acids
Lower the activation energy (energy required to start a reaction)
Increase the rate of reaction

2. Name of Enzymes End in –ase Identifies a reacting substance
sucrase – reacts sucrose
lipase - reacts lipid
Some names of digestion enzymes still use –in ending
pepsin, trypsin

3. Enzyme Action Terms Substrate-substance that enzyme acts upon
Active Site-a fold on the surface of an enzyme that fits with a specific substrate
Enzyme-Substrate-Complex-the enzyme and substrate when attached at the active site
Product-the result of the chemical reaction between the enzyme and the substrate
Substrate

4. Enzyme Action: Lock and Key Model
An enzyme binds a substrate in a region called the active site
Only certain substrates can fit the active site
Enzyme-substrate complex forms
Substrate reacts to form product
Product is released

5. Lock and Key Model
E S ES complex E P P S S P

6. Interesting Enzyme Facts
The house dust mite makes an enzyme in its gut and then places the enzyme in its droppings (poop) in order to breakdown hard-to-digest food…. for a later dinner!
Many humans are allergic to this dust mite enzyme.
It takes hours to digest a hamburger and bun plus the fixings with enzymes.
It takes a year and a half without enzymes!

7. Factors Affecting Enzyme Action: Temperature
Slow activity at low temperature
Rate increases with temperature
Most active at optimum temperatures (usually 37°C in humans)
Activity stops at high temperatures because enzyme denatures (breaks down)

8. ←Amylase ←Pepsin ←Lipase (breaks down starch) (breaks down proteins)
(breaks down lipids)

9. Factors Affecting Enzyme Action
Optimum temperature
Reaction
Rate
Low High
Temperature

10. Factors Affecting Enzyme Action: Substrate Concentration
Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant)
Maximum activity reached when all of enzyme combines with substrate

11. Factors Affecting Enzyme Action
Maximum activity
Reaction
Rate
substrate concentration

12. Factors Affecting Enzyme Action: pH
Maximum activity at optimum pH
Pepsin (breaks down protein) works best at pH5 in the human stomach
Activity stops if pH is to low or high

13. Factors Affecting Enzyme Action
Reaction
Rate
Optimum pH pH

14. Enzyme Inhibition Enzymes Inhibit Chemical Reactions
cause a loss of catalytic activity
Change the protein structure of an enzyme
May be competitive or noncompetitive
Some effects are irreversible

15. Competitive Inhibition
A competitive inhibitor
Has a structure similar to substrate
Occupies active site
Competes with substrate for active site
Has effect reversed by increasing substrate concentration

16. Noncompetitive Inhibition
A noncompetitive inhibitor
Does not have a structure like substrate
Binds to the enzyme but not active site
Changes the shape of enzyme and active site
Substrate cannot fit altered active site
No reaction occurs
Effect is not reversed by adding substrate