1. Chemical Reactions & Enzymes
Sections 2.4 & 2.5

2. 2.4 Chemical Reactions Key Concept:
Life depends on chemical reactions.

3. Bonds break and form during chemical reactions.
Chemical reactions change substances into different ones by breaking and forming chemical bonds.
Reactants are changed during a chemical reaction.
Products are made by a chemical reaction.
Endothermic and Exothermic Reactions

4. Chemical reactions release or absorb energy.
Activation energy is the amount of energy that needs to be absorbed to start a chemical reaction

5. Exothermic reactions release more energy than they absorb.
Reactants have higher bond energies than products.
Excess energy is released by the reaction.
Energy “exits” the reaction. (Exo = exit) Ex: Cellular Respiration, making ice cubes

6. Endothermic reactions absorb more energy than they release.
Reactants have lower bond energies than products.
Energy is absorbed by the reaction to make up the difference.
Energy goes into the reaction. (Endo = “into”) Ex: Photosynthesis, melting ice cubes

7. STOP & REVIEW
_________ __________change substances into different ones by breaking and forming chemical bonds.
Chemical Reactions
_____________ are changed during a chemical reaction.
Reactants
__________ are made by a chemical reaction.
Products
___________ ____________ is the amount of energy that needs to be absorbed to start a chemical reaction.
Activation Energy
______________ reactions release more energy than they absorb.
Exothermic
___________ reactions absorb more energy than they release.
Endothermic

8. 2.5 Enzymes
Key Concept:
Enzymes are catalysts for chemical reactions in living things.

9. A catalyst lowers activation energy.
Catalysts are substances that speed up chemical reactions
Decrease activation energy
Increase reaction rate

10. Enzymes allow chemical reactions to occur under tightly controlled conditions.
Enzymes are catalysts in living things.
Enzymes are needed for almost all processes.
Most enzymes are proteins.

11. Disruptions in homeostasis can prevent enzymes from functioning.
Enzymes function best in a small range of conditions.
Changes in temperature or pH can break hydrogen bonds.
An enzyme’s function depends on its structure.

12. An enzyme’s structure allows only certain reactants to bind to the enzyme.
Substrates: reactants that bind to an enzyme
Active site: area on the enzyme where substrates bind

13. Lock and key model shows how enzymes function
Substrates are brought together at the active site of the enzyme
Enzyme weakens the bonds between the substrates.
Reaction forms a product that is released from the enzyme.

14. STOP & REVIEW
_________ are catalysts for chemical reactions in living things.
Enzymes
________ are substances that speed up chemical reactions by
Catalysts
Decreasing __________ ______
Activation energy
Increasing ___________ _______
Reaction rate
Most enzymes are _______________
proteins
Changes in __________ or _____ can break hydrogen bonds.
Temperature or pH
An enzyme’s function depends on its _________
Structure
__________: reactants that bind to an enzyme
Substrates
________ _____: area on the enzyme where substrates bind
Active Site