Chapter 8 Metabolism: Energy and Enzymes Energy is the capacity to do work; cells must continually use energy to do biological work. Kinetic Energy is energy of motion; all moving objects have kinetic energy. Potential energy is stored energy. Chemical energy is in the interactions of atoms.

Two Laws of Thermodynamics: 1. Law of conservation of energy states that energy cannot be created or destroyed; it can be changed from one form to another. 2. Energy cannot be changed from one form into another without a loss of usable energy.

Entropy is the measure of randomness or disorder. Organized / usable forms of energy have low entropy. Unorganized / less stable forms have high entropy.

Chapter 8 Metabolism: Energy and Enzymes Metabolism is the sum of all the biochemical reactions in a cell. Reactants are substances that participate in a reaction Products are substances that form as a result of a reaction. A + B C+D; A and B are reactants, C and D are products

Chapter 8 Metabolism: Energy and Enzymes Free energy ( G) is the amount of energy that is free to do work after a chemical reaction. Exergonic Reactions have a negative G and energy is released. Endergonic reactions have a positive G; products have more energy than reactants; such reactions only occur with an input of energy.

Coupled reactions occur when energy released by an exergonic reaction is used to drive an endergonic reaction. Energy released from ATP ADP + P is used to fuel many biological reactions. When ATP breaks down to drive reactions, some energy is lost as heat. The overall reaction becomes exergonic. P

Chapter 8 Metabolism: Energy and Enzymes ATP is energy currency of cells; when cells require energy, they “spend” ATP. Energy released from ATP ADP + is just about enough for most biological reactions. P

Chapter 8 Metabolism: Energy and Enzymes Function of ATP: Chemical Work Transport Work Mechanical Work

Chapter 8 Metabolism: Energy and Enzymes ATP structure = a nucleotide made of base adenine, sugar ribose, and three phosphate groups. ATP = “high-energy” compound because a phosphate group is easily removed.

Chapter 8 Metabolism: Energy and Enzymes Rxns in Cells are orderly: Metabolic pathways are orderly sequences of chemical reactions; each step is catalyzed by a specific enzyme. One pathway leads to the next. Since pathways use the same molecules, a pathway can lead to several others.

Enzymes are proteins that act as catalysts to speed up chemical reactions without being changed. Energy of Activation is energy that must be added to cause molecules to react.

Enzymes speed chemical reactions by lowering the energy of activation by forming a complex with their substrate(s) at the active site. An active site is a small region on the surface of an enzyme where the substrate(s) bind.

Chapter 8 Metabolism: Energy and Enzymes Induced-fit model is when the substrate binds to an enzyme and the active site undergoes a slight change in shape that facilitates the reaction. A particular reactant may produce more than one type of product Enzymes are named for substrates by adding “-ase”.

Chapter 8 Metabolism: Energy and Enzymes Factors affecting enzymatic speed: Inquiry Lab… 1. Amount of substrate 2. Amount of enzyme 3. Temperature 4. pH 5. Inhibitors or cofactors

Chapter 8 Metabolism: Energy and Enzymes Temperature: As temperature rises, enzyme activity increases because there are more molecular collisions. Enzyme activity declines rapidly when an enzyme is denatured at a certain temperature. Denatured enzymes have lost their normal shape so that they no longer function.

Chapter 8 Metabolism: Energy and Enzymes pH: Each enzyme has an optimal pH that maintains its normal configuration. A change in pH alters ionization of side chains, eventually resulting in denaturation.

Inhibition is a common means by which cells regulate enzyme activity. Competitive inhibition occurs when another molecule is similar to an enzyme’s substrate and it competes with the true substrate for the enzyme’s active site.

Noncompetitive inhibition occurs when a molecule bind to an allosteric site and changes the 3- dimensional structure of an enzyme and its ability to bind to its substrate. An allosteric site is a regulatory binding site on an enzyme that controls the activity of that enzyme.

Many enzymes require an inorganic ion or non-protein cofactor to function. Ions are metals. The organic cofactors are coenzymes that assist enzymes or accept or contribute atoms to the reaction.

Chapter 8 Metabolism: Energy and Enzymes In oxidation-reduction (redox) reactions, electrons pass from one molecule to another. Oxidation is the loss of electrons. Reduction is the gain of electrons.

Photosynthesis uses energy to combine carbon dioxide and water to produce glucose. Water has been oxidized and carbon dioxide has been reduced. Chloroplasts capture the solar energy and convert it by electron transport system to the chemical energy of ATP.

In Cellular respiration glucose loses hydrogen atoms (oxidized) and oxygen gains hydrogen atoms (reduced). Both photosynthesis and respiration are metabolic pathways that use an electron transport system consisting of membrane- bound carriers to pass electrons from one carrier to another.

ATP synthesis is coupled to the electron transport system. Particles called ATP synthase complexes span the membrane; each complex contains a channel that allows H+ ions to flow down their electrochemical gradient. Flow of H+ ions through the channel provides the energy to drive ADP + ATP. P

Chapter 8 Metabolism: Energy and Enzymes This will all be discussed in detail in Chapters 9 and 10 (Photosynthesis and Cellular Respiration).