Ch. 2 Sec. 4

1. Ch. 2 Sec. 4 Chemical Reactions and Enzymes

2. Chemical Reaction - process that changes one set of chemicals into another set of chemicals A. Conservation of mass & energy

3. Some chemical reactions occur slowly, such as the combination of iron and oxygen to form an iron oxide called rust. • Other reactions occur quickly. For example, when hydrogen gas is ignited in the presence of oxygen, the reaction is rapid and explosive.

4. 1. The elements or compounds that enter into a chemical reaction are known as reactants 2. The elements or compounds produced by a chemical reaction are known as products

5. Chemical reactions always involve changes in the chemical bonds that join atoms in compounds In bloodstream: CO2 + H2O H2CO3 In lungs: H2CO3 CO2 + H2O

6. II. Energy in Reactions A. Energy is released or absorbed whenever chemical bonds form or are broken • Because chemical reactions involve breaking and forming bonds, they involve changes in energy

7. Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will not occur without a source of energy.

8. 1. Energy-releasing reaction in which energy is given off as heat 2H2 + O2 2H2O 2. Electrolysis (adding energy) reverses this reaction

9. In order to stay alive, organisms need to carry out reactions that require energy • Plants get their energy from the sun • Animals get their energy from eating plants or other animals

10. B. Activation Energy - energy that is needed to get a reaction started

11. Activation energy is a factor in whether the overall chemical reaction releases energy or absorbs energy. Fig. 2-19 pg. 50

12. III. Enzymes A. Catalyst - speeds up rate of reaction

13. B. Enzymes - proteins that act as biological catalysts 1. Enzymes speed up chemical reactions in cells 2. Lower activation energy

14. Lowering the activation energy has a dramatic effect on how quickly the reaction is completed. Fig. 2-20 pg. 51

15. Enzymes are very specific, generally catalyzing only one chemical reaction. • For this reason, part of an enzyme’s name is usually derived from the reaction it catalyzes. • Ex: Carbonic anhydrase • Enzyme to catalyze the reaction removing water from carbonic acid

16. IV. Enzyme Action • For a chemical reaction to take place, the reactants must collide with enough energy so that existing bonds will be broken and new bonds will be formed. • If reactants do not have enough energy, no reaction will take place.

17. A. The Enzyme-Substrate Complex • Substrates – reactants in enzyme action a. Enter enzyme b. Reaction occurs 2. Products are released 3. Enzyme is free to start process again

18. An Enzyme-Catalyzed Reaction Fig. 2-21 pg. 52

19. B. Regulation of Enzyme Activity 1. Enzymes work best at certain pH values 2. Affected by changes in temperature C. Cells can regulate the activities of enzymes D. Most cells contain proteins that help to turn key enzymes “on” and “off” at critical stages in the life of the cell

20. Enzymes play essential roles in: • regulating chemical pathways • making material that cells need • releasing energy • transferring information

21. 2–4 Chemical Reactions and Enzymes Everything that happens in an organism is based on chemical reactions. A chemical reaction is a process that changes one set of chemicals into another set of chemicals. The elements or compounds that enter into the reaction are the reactants. The elements or compounds produced by the reaction are known as products. Chemical reactions always involve breaking the bonds in reactants and forming new bonds in products.

22. Some chemical reactions release energy; others absorb energy. Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy require a source of energy. Every chemical reaction needs energy to get started. The energy that starts a chemical reaction is called activation energy.

23. Some chemical reactions that make life possible are too slow.A catalyst is a substance that speeds up the rate of a chemicalreaction. Catalysts work by lowering a reaction’s activation energy. Enzymes are proteins that act as biological catalysts. Enzymes speed up chemical reactions that take place in cells. In an enzyme-catalyzed reaction, the reactants are known as substrates. Substrates bind to a site on the enzyme called an active site. The fit of substrates binding to an active site is so specific that they are often compared to a lock and key. Substrates remain bound to the enzyme until the reaction is done. Once the reaction is over, the products are released.