IV. Chemical Reactions and Enzymes

1. IV. Chemical Reactions and Enzymes A. Chemical Reactions Chemical reaction – a process that changes one set of chemicals into another set of chemicals. Chemical reactions have 2 major parts 1. Reactants – the elements or compounds that are combined (enter) into a chemical reaction. 2. Products – the elements or compounds produced by a chemical reaction. 2H2 + O2 2H2O (Reactants) (Products)

2. Chemical Reactions H2 + Cl2     2 HCl (Reactants) (Products) -Numbers in front of element symbols = the # of molecules involved in the reaction. -Subscripts = the # of atoms in each molecule. ***Chemical reactions always involve the breaking of bonds in reactants and the formation of new bonds in products.****

3. B. Energy in Reactions -Some chemical reactions release energy & others absorb energy, ex : water formation releases energy & water break-down absorbs energy. -Energy changes determine whether a reaction will occur. -Chemical reactions that release energy are often spontaneous.

4. Activation Energy & Endo vs. Exothermic Rxns. -Chemical reactions that absorb energy won’t happen without a source of energy (activation energy). Activation energy – the energy needed to get a reaction started. -Endothermic reactions absorb heat & exothermic reactions release heat.

5. C. Types of Reactions 1. Hydrogenation – process where unsaturated fats become saturated fats by adding hydrogen. 2. Dehydration Synthesis – putting molecules together by removing water (synthesis means putting together & dehydration means removing water). -Sugar molecules bond where an OH group is present. In living cells,this bonding is due to enzymes. Examples : Glucose + Glucose = Maltose Glucose + Galactose = Lactose Glucose + Fructose = Sucrose

6. Dehydration Synthesis

7. Types of Rxns. - Hydrolysis 3. Hydrolysis – Hydro = water, Lysis = to break/split apart (by enzymes). -Is the breaking of a chemical bond by adding water to it. The bond breaks & the original OH is restored.

8. Hydrolysis

9. D. Enzymes *To stay alive, organisms must carry out reactions that require energy. -The chemical reactions that make life possible occur when cells produce catalysts – substances that speed up the rate of a chemical reaction. -Catalysts work by lowering the activation energy of a reaction. -Enzymes are proteins that act as biological catalysts ----They speed up chemical reactions that take place in cells.

10. E. Enzyme Action -Enzymes have specific sites where reactants can be brought together to react. Substrates – reactants of enzyme-catalyzed reactions. -Substrates bind to a site on the enzyme called the active site. The active site & substrates have complimentary shapes that fit exactly (like a lock & key). -Once bound together, they form an enzyme-substrate complex that remains joined until the reaction is over.

11. Regulation of Enzyme Activity Enzyme activity can be affected by : 1. pH values 2. Temperatures (body temp. is ideal) 3. Cells – can turn enzymes on or off.