1. Agenda Bell Work Review Test Enzyme Notes Define the word enzyme.
What do you now about catalysts?
Review Test
Enzyme Notes

2. Enzymes
Mrs. Ragsdale
Biology I

3. What the heck is an Enzyme?
Made up of proteins
Can act as catalysts
Catalysts speed up the rate of a reaction without ever changing itself
Speed up the rate by lowering activation energy
Enzymes are very specific to whatever they act upon (their substrate)
Can be severely affected by pH and temperature changes

4. Enzyme Active Sites
Enzymes have “active sites” where their substrate can bind to them

5. Lock and Key Model
For each enzyme there is only one specific substrate that it works for
Enzyme is the “lock” substrate is the “key”
Enzyme specificity is due to the complementary shape of the active site and the substrate.

6. Lock and Key Model a) Large globular protein enzyme
b) Active Site where the substrate combines to the enzyme
c)Substrate which fits the active site
d) Activated complex. The substrate is weakened to allow the reaction.
e)Unchanged enzyme/ re- used at low concentrations
f) Product of the reaction

7. Artist Rendition vs Reality

8. So how do enzymes work exactly?
Enzymes speed up metabolic reactions by lowering activation energy
Activation energy – the energy required to start a reaction

9. Agenda Bell Work Notes Enzymes What is an enzyme made of?
What is a substrate?
What does this phrase mean: Enzyme Specificity
Notes Enzymes

10. Temperature and Enzymes
When temperature increases, bonds start breaking inside the enzyme because it was made of protein
Increased temperature also increased kinetic energy so molecules are coming together more rapidly

11. pH and Enzymes Enzymes also have a narrow range of pH tolerance
Too high or too low will decrease enzyme activity

12. Substrate Concentration and Enzymes
Typically, the more substrate you have the faster the reaction rate
More substrate = more collisions between enzyme and substrate
The more substrate added, you begin to see diminishing returns until eventually the rate is constant

13. Denaturation
A structural change in a protein that results in the loss (usually permanent) of its biological processes
Caused by heat and pH

14. Temperature and Denaturation
Temp inc = kinetic energy increase
More vibrations between molecules
Breaks hydrogen bonds
Shape of enzyme breaks
Active site is no longer accessible to substrate

15. Denaturation and pH Low pH = high H⁺ High pH = high OH⁻
H⁺ just LOVES to bind with the electronegative areas on enzymes
Causes the shape of the enzyme to change
Substrate can no longer bind to enzyme
High pH = high OH⁻
OH⁻ is an H⁺ thief and will steal hydrogen ions from the enzyme
Again, causes change in shape
Substrate can no longer bind to the enzyme

16. Real Life Example: How we use enzymes every day
Around 90% of all humans eventually become intolerant to lactose
No longer able to digest the sugars in milk = no ice cream = bad.
Lactase is an enzyme that can digest lactose into its base sugars glucose + galactose

17. Removing that nasty lactose!
Method 1
Just add some lactase
Method 2
Immobilize the lactase on a porous surface
Pour the milk over the surface to remove the lactose
No lactose or lactase in the milk

18. Metabolic Pathways and Induced Fit

19. Metabolic Pathways Chains and cycles of enzyme-catalysed reactions
Each stage of the reaction features its own enzymes
Metabolic pathways are chains of chemical reactions carried out in a particular sequence
Anabolic pathways – build up organic compounds
Catabolic pathways – break down organic compounds

21. Induced Fit Model Lock and Key method incomplete
Does not explain how substrate binds to the active site
Until a substrate binds to the active site, it does not actually fit precisely
Induced Fit Model states that the substrate induces the active site to change
The bonds within the substrate weaken
Lowers the activation energy
Allows the reaction to occur

23. Enzymes and Activation Energy
Enzymes work by lowering activation energy
The energy required for the reaction to take place
Exergonic or exothermic reactions

24. Enzyme Inhibition
An economical way to control metabolic pathways in your body
Inhibits the production of the end product at the beginning of the metabolic pathway
Prevents the build-up of intermediate products

25. Allosteric Interactions
An allosteric enzyme is the enzyme that regulates one of the first reactions in a metabolic pathway.
Allosteric enzymes have two non-overlapping binding sites – active site and allosteric site.
Once bound at the allosteric site, the structure of the enzyme is altered so that the substrate is less likely to bind to the active site

27. Competitive Inhibition
Substrate and Inhibitor are similar in shape
Inhibitor is able to bind to the active site and thereby block the substrate
Only slows down the rate of the reaction, not stop it completely
Increasing the concentration of the substrate would allow the substrate to out compete the inhibitor

29. Competitive Inhibition Example
Methanol poisoning occurs because methanol is oxidized to formaldehyde and formic acid which attack the optic nerve causing blindness.
Ethanol is given as an antidote for methanol poisoning because ethanol competitively inhibits the oxidation of methanol.
Ethanol is oxidized in preference to methanol and consequently, the oxidation of methanol is slowed down so that the toxic by-products do not have a chance to accumulate.

30. Noncompetitive Inhibition
Substrate and inhibitor are different in shape
Inhibitor binds to a region on the enzyme other than the active site
Causes structural changes to the enzyme allowing the active site to change shape
Prevents substrate from being able to bind – results in a decrease in activity

32. Noncompetitive Inhibition Example
Oxalic and citric acid inhibit blood clotting by forming complexes with calcium ions necessary for the enzyme metal ion activator.