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Energy and Enzymes • What is energy? Energy is the capacity to do work. Cells continually use energy to develop, grow, repair, reproduce, etc. Forms of Energy • Kinetic energy ▫ Motion ▫ All moving objects have kinetic energy • Potential energy ▫ Stored • Chemical energy ▫ Food ▫ Contains potential energy • Mechanical energy ▫ Muscle movement. ▫ Chemical energy needed First law of thermodynamics • Law of Conservation of Energy • Energy cannot be created or destroyed, but it can be changed from one form to another. • Example: ▫ Photosynthesis converts solar energy into chemical energy. Second law of thermodynamics • Energy cannot be changed from one form into another without a loss of usable energy. • Heat is a form of energy that dissipates into the environment • Heat can never be converted back to another form of energy. ATP: Energy for Cells • Adenosine triphosphate (ATP) is the energy currency of cells. • When cells need energy, they “spend” ATP. • ATP supply is maintained by breakdown of glucose during cellular respiration. Adenosine Triphosphate • ATP is a nucleotide. • Adenosine • Ribose- sugar • Three phosphate groups • ATP is an energy carrier for many different types of reactions. ATP to ADP • When ATP is converted into ADP (adenosine diphosphate) when one phosphate group is removed. • About 7.3 kcal of energy is released per mole of ATP. Metabolic Reactions • 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. 2 Types of Metabolic Reactions Catabolic • Breakdown of larger molecules to produce energy Anabolic • energy‐consuming synthesis of cellular components from smaller molecules Exergonic reactions • The products have less free energy than reactants • Reaction will occur spontaneously. • Tend to be catabolic Endergonic reactions • Products have more energy than reactants; • Reactions can only occur with an input of energy. • Tend to be anabolic Energy of Activation • Reactions often require activation. • The energy of activation (Ea) is the energy that must be added to cause molecules to react. • For metabolic reactions to occur in a cell, an enzyme must usually be present. Enzymes • Proteins and catalysts • Speed chemical reactions. • Every enzyme is specific in its action and catalyzes only one reaction or one type of reaction. • Control the rate of chemical rxns by weakening bonds, thus lowering the amount of activation energy needed for the reaction Enzyme-Substrate Complex • Enzymes lower the energy of activation by forming a complex with their substrate(s) at the active site • Substrates are the reactants • Active site is a small region on the surface of the enzyme where the substrate(s) bind, then change in shape facilitating the reaction. 16 Enzyme + Substrate = Product 17 How the Enzyme Works Enzymes are reusable!!! Active site changes SHAPE Called INDUCED FIT Factors Affecting Enzymatic Speed • Substrate concentration. • Optimal pH • Temperature 19 Denaturating Proteins Changes in temperature & pH can denature (unfold) a protein so it no longer works Cooking denatures protein in eggs Milk protein separates into curds & whey when it denatures Enzymes in Everyday Life http://youtu.be/E90D4BmaVJM