1. 2.4: Chemical Reactions & Enzymes
chemical reaction: process that changes one set of chemicals into another by changing the chemical bonds that join the atoms
elements (or compounds) that enter into a chemical reaction are known as reactants & those produced by a chemical reaction are known as products
reactants products

2. energy is released or absorbed during chemical reactions
chemical reactions that release energy usually occur on their own
chemical reactions that absorb energy will not occur without a source of energy

3. every organism must have a source of energy to carry out the chemical reactions it needs to stay alive
plants get their energy by trapping and
storing the energy from sunlight in
energy-rich compounds
animals get their energy when they eat plants or other animals

4. energy that is needed to get a reaction started is called the activation energy
activation energy is involved in chemical reactions whether or not the overall reaction releases or absorbs energy

5. some chemical reactions are too slow or have activation energies that are too high to make them practical for living organisms
these chemical reactions are made possible by catalysts
catalyst: substance that speeds up the rate of a chemical reaction
work by lowering a reaction’s activation energy

6. enzymes: globular proteins that act as biological catalysts
thousands of different enzymes exist in the body & can be reused
enzymes are very specific, catalyzing only one chemical reaction

7. enzymes weaken the bonds which lowers the amount of activation energy needed for the reaction7 7

8. reactants of enzyme-catalyzed reactions are known as substrates
Joins 8

9. substrates bind to a site on the enzyme called the active site9

10. active site & substrates have complementary shapes which explains why they are specific to a particular reaction
Enzyme

11. temperature, pH, and regulatory molecules are all factors that can affect enzyme activity
best close to normal body temperature & with a pH between 6 – 8
~ extremes tend to unfold the enzyme
most enzymes are regulated by molecules that carry chemical signals (hormones!) within cells, switching enzymes “on” or “off” as needed

12. Enzyme Animation: