1. Enzymes
Chapter 6

2. What Are Enzymes? Catalysts-
substances that speed up a reaction
Enzymes – biological catalysts
Proteins
Reactions are too slow; need to speed up in order to maintain life

3. Reactions For reactions to energy barrier must be overcome
Exergonic reactions
proceed only after the reactants are pushed over energy barrier
Ex: Propane + oxygen
Need to have a spark to start reaction
Pushed over energy barrier
Activation Energy (Ea)
The amount of energy needed to start the reaction

5. Activation Energy (Ea)
Amount of energy needed to start the reaction
Transition-state species:
Energy needed to change reactants into unstable molecular forms
Chemical bonds stretch & become unstable
Activation energy can come from reactants kinetic energy from motion
Does not work in living systems
Enzymes
lower the energy barrier by bringing the reactants together.

6. Enzymes ENZYMES lower the energy barrier
Bring the reactants into close proximity to each other
Biological catalysts are highly specific
Enzyme recognizes & binds to only one or a few closely related reactants
Names of enzymes represent their function & usually end in “-ase”

7. Enzymes Substrates Active Site Enzyme-Substrate Complex (ES)
Reactants in enzyme-catalyzed reaction
Active Site
Where catalysis takes place
Enzyme-Substrate Complex (ES)
The binding of a substrate to the active site
E + S ES E + P

8. How Enzymes Work Chemical interaction occur in the ES complex
Break old bonds & form new ones
Enzymes use the following mechanisms
Enzymes orient substances
Orient to ensure correct bonds are formed
Enzymes induce strain in the substance
Stretches the bonds to create unstable transition state
Enzyme temporarily add chemical groups to substrates

10. How enzymes work Enzyme
Contain hundreds of amino acids usually with a single fold
Active site is quite small (6-12 amino acids)
Helps select the right substrates
Enzyme changes shape when substrates bind: induced fit
Ensures the substrates are properly positioned

11. Enzymes Some enzymes require “partners” to function Prosthetic group
Non-amino acids atoms or molecules that are permanently bound
Cofactors
Inorganic ions that bind to enzymes (essential to function)
Copper, zinc, iron
Coenzymes
Required for certain actions of enzymes
Carbon-containing atom
Help add and/or remove chemical groups from substrates
ATP & ADP are necessary for reactions; considered coenzymes
Vitamins

13. Metabolic Pathway Metabolic Pathway Systems biology
Chemical reactions that occur one right after the other
Product of one is the reactant for the next
Pathways are interconnected; helps maintain homeostasis
Systems biology
Study of metabolic pathways

15. Inhibitors Inhibitors Natural inhibitors Artificial inhibitors
Slow down the rate of enzyme-catalyzed reactions
Natural inhibitors
Regulates metabolism
Artificial inhibitors
Treat diseases, kills pests

16. Inhibitors Irreversible inhibitors Reversible Covalently bonds
permanently inactivating the enzymes
Nerve gas
Reversible
Bonds non-covalently to active site
Prevents substrates from bonding
Competitive inhibitor
Binds elsewhere causing enzyme to change shape & alter active site
Noncompetitive inhibitor

17. Irreversible inhibitor

18. Reversible Inhibitor

19. Affects of enzyme activity
Environment pH
Each have an ideal pH
Activity decreases the more acidic or basic a solution becomes
Temperature
High temperature non-covalent bonds break
Enzymes denature

20. Isozymes:
enzymes that catalyze the same reaction but have different properties, such as optimal temperature.
Organisms can use isozymes to adjust to temperature changes.
Enzymes in humans have higher optimal temperature than enzymes in most bacteria—a fever can denature the bacterial enzymes.