Chemical Reactions & Enzymes

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