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CHAPTER FIVE • About 75% of the energy generated by a car’s engine is lost as heat • You’d have to run 14 miles to burn the calories from one large pepperoni pizza SOME BASIC ENERGY CONCEPTS • Energy makes the world go around – what is energy? • Energy is the capacity to perform work Conservation of Energy • Kinetic energy is energy in motion • Potential energy is energy in storage 2 High potential energy 1 Conversion of kinetic energy to potential energy 3 4 Low potential energy Conversion of potential energy to kinetic energy Conservation of Energy • Energy can be converted from one form to another but it cannot be created or destroyed Heat • Heat is – a type of kinetic energy – randomized energy Chemical Energy • Chemical energy – is a form of potential energy – is found in food, gas, and other fuels Fuel rich in chemical energy Gasoline Waste products poor in chemical energy Heat energy Carbon dioxide Combustion Kinetic energy of movement Oxygen Water (a) Energy conversion in a car Heat energy Food Oxygen Cell respiration Energy for cellular work (b) Energy conversion in a cell Carbon dioxide Water • Cell respiration – is the energy-releasing chemical breakdown of fuel molecules Food Calories • A calorie is the amount of energy that raises the temperature of 1 gram of water by 1 degree Celsius • 1 Calorie = 1,000 calories – the unit used to measure the energy in food ATP AND CELLULAR WORK • The chemical energy of organic molecules is released in cell respiration to make ATP • This release occurs in the mitochondria The Structure of ATP • ATP (Adenosine TriPhosphate) – adenosine plus three phosphate groups Energy Adenosine Adenosine Phosphate transferred to other molecules ENZYMES • Metabolism is defined as all of the chemical reactions that occur in organisms; rate? • Few metabolic reactions occur without the assistance of enzymes Activation Energy • Activation energy – the minimum energy required to activate the reaction • Enzymes – lower the activation energy for chemical reactions Enzyme Activation energy barrier Reactants Products (a) Without enzyme (b) With enzyme Selective • Each enzyme is very selective • Each enzyme fits to one specific substrate – the active site fits to the substrate and the enzyme changes shape slightly; induced fit • Enzymes are reusable Substrate (sucrose) 1 Enzyme available with empty active site 2 Substrate binds Active site to enzyme Enzyme (sucrase) Fructose Glucose 4 Products are released 3 Substrate is converted to products Enzyme Inhibitors • Enzyme inhibitors – inhibit a metabolic reaction – bind to the active site, as substrate impostors Inhibitor Substrate Substrate Active site Active site Enzyme (a) Normal enzyme action Enzyme (b) Enzyme inhibition by a substrate imposter Passive Transport: Diffusion Across Membranes • Molecules contain heat energy – they vibrate and wander randomly • Diffusion is one result of the movement of molecules – molecules tend to spread into the available space – diffusion is passive transport; no energy is needed Molecules of dye Membrane Equilibrium (a) Passive transport of one type of molecule Equilibrium (b) Passive transport of two types of molecules Osmosis and Water Balance in Cells • Osmosis is the passive transport of water across a selectively permeable membrane Hypotonic solution Hypertonic solution Isotonic solutions Sugar molecule (solute) Selectively permeable membrane Osmosis (net movement of water) Water Balance in Cells • The survival of a cell depends on its ability to balance water uptake and loss Animal cell Normal Lysing Shriveled Plasma membrane Plant cell Flaccid (wilts) (a) Isotonic solution Turgid (b) Hypotonic solution Shriveled (c) Hypertonic solution Active Transport • Active transport requires energy to move molecules across a membrane Lower solute concentration Solute Higher solute concentration Exocytosis and Endocytosis: Traffic of Large Molecules • Exocytosis – secretes substances outside of the cell Outside cell Plasma membrane Cytoplasm (a) Exocytosis • Endocytosis – takes material into the cell (b) Endocytosis
