IV. pH H2O H+ + OH- A. Dissociation of Water Molecules: 1. Water molecules split to form ions. (hydroxide ion) H2O H+ + OH-

*The dissociation of water is reversible. + OH- H2O

2. In pure water, H+ and OH- are equal in concentration. 3. Certain substances can cause imbalances in these concentrations. a. These substances are called ACIDS and BASES.

B. Acids 1. Add (donate) more H+ when dissolved in water. 2. More H+ = stronger acid 3. Taste sour Example: HCl  H+ and Cl-

C. Bases 1. Add more OH- when dissolved in water. 2. More OH- = stronger base 3. Alkaline 4. Taste bitter Example: NaOH  Na+ and OH-

The measure of how acidic or basic a compound is D. pH scale The measure of how acidic or basic a compound is Neutral 7 1 2 3 4 5 6 8 9 10 11 12 13 14 strong weak weak strong Basic Acidic [H+] > [OH-] [H+] < [OH-]

IV. Enzymes Enzymes are proteins that act as organic biological catalysts by speeding up the rate of chemical reactions (breaking/forming of bonds). 1. They work by lowering the amount of energy needed to start a reaction (activation energy) 2. They are reusable.

B. Substrate: what an enzyme breaks down or puts together. Ex: Maltase – the enzyme that works with the sugar, maltose The first part of the enzyme name indicates the substrate that it works with. Enzyme names end in -ase glucose glucose Maltose Maltase Enzyme-Substrate Complex

Dehydration Synthesis Substrate Enzyme Enzyme-Substrate Complex

Hydrolysis Substrate Enzyme Enzyme-Substrate Complex

C. Enzyme activity: 1. The Enzyme – Substrate Complex: a. Lock and Key Model – enzymes work on specific substrates *Each enzyme (“lock”) has an active site with a specific shape in which the substrate (“key”) fits.

b) Induced Fit – the active site closes snugly around the substrate. *like a hand catching a ball 2. Coenzymes: bind to the active site to help enzymes do their job. *vitamins are coenzymes

D. Factors affecting enzyme activity: *each enzyme works best in certain conditions. The concentration of enzymes vs. substrates – how often they bump into each other. PICTURE

2. Temperature: as temperature increases, the rate of reaction increases….. *but if it gets too hot… the enzyme denatures (changes shape) and no longer functions 37°C = Body Temp. Above 40°C = Denatures

3. pH Level: Enzymes work best within a certain pH range. *if the pH is too low or too high, the enzyme will denature.