1. Lecture # 5: Energy and Chemical Reactions (Chapter 2) Objectives: Cholesterol crystals seen through a polarizing microscope 1- Symbolize chemical reactions with chemical equations. 2- Identify the factors that govern the speed and direction of a reaction. 3- Define metabolism and its two subdivisions. 4- Define oxidation and reduction and relate these to changes in the energy content of a molecule.

2. Chemical Reactions It is a process in which a covalent or ionic bond is formed or broken The course of a chemical reaction is symbolized by a chemical equation: Chemical Reaction: reactants (on left) products (on right) CH 3 CH 2 OH + O 2 EthanolOxygen CH 3 CHOOH + H 2 O Acetic acidWater Classes of Chemical Reactions Exchange reactions: Decomposition reactions: Synthesis reactions: Large molecule breaks down into two or more smaller ones Two or more small molecules combine to form a larger one Two molecules exchange atoms or group of atoms

3. Decomposition Reactions Large molecule breaks down into two or more smaller ones AB  A + B Starch molecule Glucose molecules (a) Decomposition reaction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

4. Synthesis Reactions Two or more small molecules combine to form a larger one A + B  AB Amino acids Protein molecule (b) Synthesis reaction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5. Exchange Reactions Two molecules exchange atoms or group of atoms AB + CD  ABCD  AC + BD Stomach acid (HCl) and sodium bicarbonate (NaHCO 3 ) from the pancreas combine to form NaCl and H 2 CO 3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. NaHCO 3 + HClH 2 CO 3 + NaCl

6. Reversible Reactions: They are reactions that can go in either direction under different circumstances CO 2 + H 2 OH 2 CO 3 CO 2 + H 2 O H 2 CO 3 HCO 3 - + H + Carbon dioxide WaterCarbonic acid Bicarbonate ion Hydrogen ion This is the most common equation discussed in this book, especially in respiratory, urinary, and digestive physiology Law of Mass Action: A chemical reaction proceeds from the side of equation with greater quantity of reactants to the side with the lesser quantity When the ratio of products to reactants is stable in reversible reactions, the Equilibrium has been reached

7. Reaction Rates Basis for chemical reactions is molecular motion and collisions. Reactions occur when molecules collide with enough force and the correct orientation Reaction Rates are affected by: 3- Catalysts 1- Concentration 2- Temperature Reaction rates increase when the reactants are more concentrated because molecules are more crowded and collide more frequently. Reaction rates increase when the temperature rises, because heat causes molecules to move more rapidly and collide with greater force and frequency Catalysts are substances that temporarily bond to reactants, hold them in favorable position to react with each other, and may change the shapes of reactants in ways that make them more likely to react. Enzymes are the most important biological catalysts

8. Metabolism, Oxidation, and Reduction All the chemical reactions of the bodyMetabolism: Catabolism Anabolism It consists of all the energy releasing (exergonic) decomposition reactions Products (Carbon Dioxide) EXERGONIC REACTION EXERGONIC REACTION CO 2 2 2 2 2 2 Reactants (Glucose) More energy Less energy ENERGY Decomposition Reaction Reactions in which the starting set of molecules (reactants) contains more energy than the final set of molecules (products). They release energy. Exergonic Reactions:

9. Anabolism: It consists of all the energy storing (endergonic) synthesis reactions ENERGY Synthetic Reaction ENDERGONIC REACTION ENDERGONIC REACTION Reactants (aminoacids) Less energy More energy Product: (Protein) Reactions in which the products contain more energy than the reactants. They consume energy Endergonic Reactions:

10. co 2 2 2 2 2 2 Energy Glycogen Exergonic Endergonic Exergonic Anabolism is driven by the energy that catabolism releases, so endergonic and exergonic reactions, anabolism and catabolism, are coupled Catabolism Anabolism ATP

11. A B Oxidation: It is any chemical reaction in which a molecule gives up electrons and releases energy. The molecule is oxidized in this process When one molecule gives up electrons, undergoes oxidation and looses energy e - e - e - When one molecule gains electrons, undergoes reduction and gains energy High-energy reduced state Low-energy oxidized state High-energy reduced state It is any chemical reaction in which a molecule gains electrons and energy Reduction: Oxidizing Agent Oxidation of one molecule is always accompanied by the reduction of another Low-energy oxidized state High-energy reduced state Ae - B+ Low-energy oxidized state High-energy reduced state Be - A+ Oxidation-reduction (redox) Reactions AB e - e - e - Reducing Agent