Cell Energetics Concept Review Energy: Big Idea in Science • Energy flows in one direction, energy never cycles back to its source What is energy? • Energy is the capacity to do work • Work is the transfer of energy • Using the definition, explain how ATP is a form of energy. There are different forms of energy: • • • • • Light Chemical Heat Potential Energy: Stored energy Kinetic Energy: Energy of motion The 1st Law of Thermodynamics • The total amount of energy in the universe is constant. Energy can’t be created or destroyed, it can only change forms. • EVERY energy transfer results in some energy being lost to the environment as heat. Energy transfers are NEVER 100% efficient. Example in Biology The 2nd Law of Thermodynamics (The Law of Entropy) • In the absence of energy inputs, an organized system becomes more disorganized over time. • Organized Disorganized • Concentrated Diffuse • Complex Simple Example in Biology Energy Reactions Endergonic Reactions Exergonic Reactions • Net increase of usable energy (energy in), transforming CO2 and H2O to glucose. • Net decrease of usable energy (energy out), transforming glucose to CO2 and H2O. • A + B + energy AB • AB Energy + A + B Metabolic Pathways Biosynthetic Pathway (Anabolic) • Metabolic pathway where small molecules are used to build larger molecules of higher bond energy. • Example: The synthesis of carbohydrates in photosynthesis. Degradative Pathway (Catabolic): • Exergonic pathways that breaks down large molecules to smaller ones. • Example: Cellular respiration Coupled Reaction • The use of an exergonic reaction to drive an endergonic reaction. ATP is responsible for mediating most energy coupling in cells. • Example: Energy from ATP is transferred to glucose to initiate glycolysis The Structure of Adenosine Triphosphate (ATP) • ATP (adenosine triphosphate) is the cell’s energy shuttle • ATP is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups How is Energy Released from ATP? •Energy is released when the terminal phosphate bond is broken during hydrolysis ATP Energy Transfer • Enzymes couple the energy of ATP hydrolysis directly to endergonic reactions by transferring a phosphate group from ATP to another molecule. • The recipient of the phosphate group has been “phosphorylated”. Substrate Level Phosphorylation • Enzymes directly transfer a phosphate group from a substrate of a reaction to ADP. • Example: The formation of ATP from PGAL during glycolysis. Electron Transfer or Oxidative Phosphorylation • The production of ATP using energy derived from the redox reactions of and electron transport chain. • The combined processes of chemiosmosis and electron transport Chemiosmosis • An energy coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane through ATP Synthase to drive cellular work such as the synthesis of ATP. • What drives ATP synthase to form ATP Enzyme Induced Fit Model • There are weak interactions between an enzyme and its substrate upon binding which induce change in the enzyme’s shape.