Energy Transformation, Cellular Energy & Enzymes (Outline)
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Energy Transformation, Cellular Energy & Enzymes (Outline) • Energy conversions and recycling of matter in the ecosystem. • Forms of energy: potential and kinetic energy • The two laws of thermodynamic and definitions • Chemical reactions and energy transformation • Biochemical metabolic reactions and pathways • Coupling energy consuming biochemical reactions with the energy releasing reaction of ATP dissociation • Types of cellular work that require energy (ATP) • Role of enzymes in catalyzing biochemical reactions • Biochemical composition of enzymes and the physical and chemical factors that regulate their activity • Competitive and non-competitive inhibitors of enzymes. Figure 1.4-0 ENERGY FLOW Sun Inflow of Outflow of light energy heat Consumers (animals) Producers (plants) Chemical energy Leaves take up in food Decomposers such CO2 from air; roots as worms, fungi, absorb H2O and and bacteria return minerals from soil chemicals to soil Figure 1.4-1 ENERGY FLOW Sun Inflow of Outflow of light energy heat Consumers (animals) Producers (plants) Chemical energy Leaves take up in food Decomposers such CO2 from air; roots as worms, fungi, absorb H2O and and bacteria return minerals from soil chemicals to soil Energy is the capacity to do work – Kinetic energy is the energy of motion – Potential energy is stored energy that can be converted to kinetic energy • Chemical bonds are a form of potential energy that can be transformed to energize cellular work The field of study of energy transformations is Thermodynamics • The First Law of Thermodynamics Energy can not be created or destroyed, it can be transformed from one form to another • The Second Law of Thermodynamics Energy transformations increase disorder or entropy of the universe, and some energy is lost as heat. Energy transformation is not 100% efficient Heat Chemical reactions Carbon dioxide + Glucose + ATP ATP water Oxygen Energy for cellular work Figure 5.2B Chemical reactions either store or release energy Endergonic reactions absorb energy and form products rich in potential energy Products Amount of energy Energy required required Reactants Potential energy of molecules Figure 5.3A Exergonic reactions release energy and yield products that contain less potential energy than their reactants Reactants Amount of energy Energy released released Products Potential energy of molecules Figure 5.3B Cells carry out thousands of chemical reactions some exergonic and others endergonic Cellular metabolism is the sum of all chemical reactions that take place inside the cell Energy coupling uses exergonic reactions to fuel endergonic reactions – ATP powers cellular work by shuttling chemical energy – The energy in an ATP molecule lies in the bonds between its phosphate groups Adenosine Triphosphate Adenosine diphosphate Phosphate groups H2O P P P P P + P Energy Hydrolysis + Adenine Ribose ATP ADP Figure 5.4A ATP hydrolysis is the main exergonic reaction used in cellular energy coupling ATP hydrolysis transfers a phosphate group to a molecule (phosphorylation). A phosphorylated molecule has a higher potential energy making it possible for the reaction to take place. ATP is a renewable resource that cells regenerate ATP Energy from Energy for exergonic endergonic reactions reactions ADP + P Figure 5.4C Types of Cellular Work ATP Chemical work Mechanical work Transport work Membrane protein Solute P + Motor protein P Reactants P P P Product P Molecule formed Protein moved Solute transported Figure 5.4B ADP + P ENZYMES • Proteins that function as catalysts for biochemical reactions • Have a conformation (3D shape) that determines their specific binding to reactants (substrates) • Lower the energy barriers of chemical reactions For a chemical reaction to begin reactants must absorb some energy, called the energy of activation EA barrier Enzyme Reactants 1 Products 2 Figure 5.5A A protein catalyst called an enzyme can decrease the energy of activation needed to begin a reaction EA without enzyme EA with enzyme Reactants Net Energy change in energy Products Progress of the reaction Figure 5.5B Enzymes, as proteins, have unique three- dimensional shapes that determine which chemical reactions occur in a cell Each enzyme catalyzes a specific cellular reaction The catalytic cycle of an enzyme 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Enzyme Glucose (sucrase) Fructose H2O 4 Products are released 3 Substrate is converted to products Figure 5.6 The cellular environment affects enzyme activity – Temperature, salt concentration, and pH – Some enzymes require non-protein components Cofactors- metal ions Coenzymes- organic molecules (vitamin derivatives) – Enzyme inhibitors interfere with an enzyme’s activity – A competitive inhibitor takes the place of a substrate in the active site – A noncompetitive inhibitor alters an enzyme’s function by changing its shape Substrate Active site Enzyme Normal binding of substrate Competitive Noncompetitive inhibitor inhibitor Enzyme inhibition Figure 5.8 Many poisons, pesticides, and drugs are enzyme inhibitors .