Bioenergetics Learning Objectives 1.Compare the difference between potential and kinetic energy. 2.Define the two laws of thermodynamics and explain how they relate to biological systems. 3.Explain how ATP functions as an energy shuttle. 4.Describe how enzymes speed up chemical reactions. Bioenergetics 5.Describe how cellular respiration produces energy that can be stored in ATP. 6.Describe the three main stages of cellular respiration. 7.Discuss the importance of oxidative phosphorylation in producing ATP. 8.Compare ATP generation from substrate level phosphorylation and oxidative phosphorylation. 9.Compare cellular respiration and fermentation. Energy Transformation in cells Energy • Cells are small units, a chemical factory, Energy is the capacity to cause change or to housing thousands of chemical reactions. perform work. • Cells use these chemical reactions for There are two kinds of energy: – cell maintenance, • Kinetic energy is the energy of motion. – manufacture of cellular parts, and • Potential energy is energy that matter – cell replication. possesses as a result of its location or structure. Fuel Energy conversion Waste products Types of Energy used by Cells Heat energy • Heat or thermal energy, is a type of kinetic Gasoline Carbon dioxide energy associated with the random movement + + Combustion of atoms or molecules. Kinetic energy of movement • Light is kinetic energy, and can be harnessed to Oxygen Water Energy conversion in a car power photosynthesis. • Electrical energy used in the nervous system. Heat energy • Chemical energy is responsible for all the Cellular respiration biochemical reactions in the cell like ATP Glucose Carbon dioxide + + ATP ATP Oxygen Energy for cellular work Water Energy conversion in a cell Sengupta 1 Bioenergetics Thermodynamics • “Thermodynamics, science of the relationship between heat, work, temperature, and energy. In broad terms, thermodynamics deals with the transfer of energy from one place to another and from one form to another. The key concept is that heat is a form of energy corresponding to a definite amount of mechanical work”. Encyclopedia Britannica • Scientists use the word – system for the matter under study and – surroundings for the rest of the universe. Biological Thermodynamics Energy Transformations • Quantitative study of the energy transductions Two laws govern energy transformations in that occur in and between living organisms, living organisms. structures, and cells and of the nature and – The first law of thermodynamics, energy in function of the chemical processes underlying the universe is constant, (statement of the these transductions. conservation of energy)and • Biological thermodynamics may address the – The second law of thermodynamics, energy question of whether the benefit associated conversions increase the disorder of the with any particular phenotypic trait is worth universe. the energy investment it requires. • Entropy is the measure of disorder, or randomness. 9 Energy Transformaon Energy Transformations in Cells • Cells use oxygen in reactions that release energy from fuel molecules. • In cellular respiration, the chemical energy stored in organic molecules is converted to a form that the cell can use to perform work. Sengupta 2 Bioenergetics Energy and Chemical reactions Exergonic reactions • Chemical reactions either Exergonic reactions release energy. – release energy (exergonic reactions) – These reactions release the energy in covalent or bonds of the reactants – require an input of energy and store – Burning wood releases the energy in glucose as energy (endergonic reactions). heat and light – Cellular respiration • involves many steps, • releases energy slowly, and • uses some of the released energy to produce ATP. Exergonic Reaction Endergonic Reactions Endergonic reaction Reactants – requires an input of energy and – yields products rich in potential energy. Amount of energy released Endergonic reactions Energy – begin with reactant molecules that contain Products relatively little potential energy but – end with products that contain more chemical energy. Potential energy of molecules Endergonic Reaction Photosynthesis : endergonic reaction Photosynthesis is a type of endergonic Products process. – Energy-poor reactants, carbon dioxide, and Amount of water are used. energy – Energy is absorbed from sunlight. Energy required – Energy-rich sugar molecules are produced. Reactants Potential energy of molecules Sengupta 3 Bioenergetics The Energy Cycle Metabolism • A living organism carries out thousands of endergonic and exergonic chemical reactions. • Metabolism :The total of an organism’s chemical reactions. • Metabolism = Anabolism + Catabolism • A metabolic pathway is a series of chemical reactions that either – builds a complex molecule or – breaks down a complex molecule into simpler compounds. Metabolic pathways Energy Coupling Breakdown Proteins to Amino Acids, Starch to Glucose • Energy coupling uses the – energy released from exergonic reactions to drive – essential endergonic reactions, – usually using the energy stored in ATP molecules. Synthesis Amino Acids to Proteins, Glucose to Starch The Energy Currency of the Cell Renewable cellular energy: ATP • ATP is a renewable source of energy • ATP, adenosine triphosphate, powers for the cell nearly all forms of cellular work. • In the ATP cycle, energy released in an exergonic reaction, such as the • ATP consists of breakdown of glucose,is used in an – the nitrogenous base adenine, endergonic reaction to generate ATP – the five-carbon sugar ribose, and – three phosphate groups. Sengupta 4 Bioenergetics Figure 5.12A_s1 ATP: Adenosine Triphosphate ATP drives cellular work Phosphate group • Hydrolysis of ATP releases energy by transferring its third phosphate from ATP P P P Adenine to some other molecule in a process Ribose called phosphorylation. • Most cellular work depends on ATP energizing molecules by phosphorylating them. ATP: Adenosine Triphosphate ATP drives cellular work Phosphate group P P P • There are three main types of cellular Adenine work: Ribose 1. chemical, 2. mechanical, and H O Hydrolysis 2 3. transport • ATP drives all three of these types of work P P P Energy ADP: Adenosine Diphosphate Chemical work Mechanical work Transport work ATP ATP ATP Solute HOW ENZYMES FUNCTION P Motor P protein P Reactants Membrane protein P P P Product Molecule formed Protein filament moved Solute transported ADP P ADP P ADP P Sengupta 5 Bioenergetics Biological Catalysts The Energy of Activation • Although biological molecules possess • We can think of EA much potential energy, it is not – as the amount of energy needed for a reactant released spontaneously. molecule to move “uphill” to a higher energy – An energy barrier must be overcome but an unstable state before a chemical reaction can begin. – so that the “downhill” part of the reaction can begin. – This energy is called the activation • One way to speed up a reaction is to add energy (E ). A heat, – which agitates atoms so that bonds break more easily and reactions can proceed but – but could also kill a cell. Reaction without enzyme Enzymes lower energy of activation Activation energy barrier Enzymes • are usually proteins, although some RNA molecules can function as enzymes. Reactant • function as biological catalysts by lowering the EA needed for a reaction to begin, • increase the speed of a reaction without being Energy consumed by the reaction Products Reaction with enzyme Metabolic reaction in a cell with and without enzyme Enzyme Activation energy a barrier Reactant reduced by b enzyme Reactants Energy Energy c Products Products Progress of the reaction Sengupta 6 Bioenergetics Figure 5.14_s2 1 Enzymes have a specific shape Enzyme available with empty active site • An enzyme Active site Substrate (sucrose) – is very selective in the reaction it catalyzes and 2 Substrate binds to enzyme with – has a shape that determines the induced fit enzyme’s specificity. Enzyme (sucrase) • The specific reactant that an enzyme acts on is called the enzyme’s substrate. • A substrate fits into a region of the enzyme called the active site. • Enzymes are specific because their active site fits only specific substrate molecules. Figure 5.14_s3 1 Enzyme available 1 Enzyme available with empty active with empty active site site Active site Substrate Active site Substrate (sucrose) (sucrose) 2 Substrate binds 2 Substrate binds to enzyme with to enzyme with induced fit induced fit Enzyme Enzyme (sucrase) Glucose (sucrase) Fructose H2O H2O 4 Products are released 3 Substrate is 3 Substrate is converted to converted to products products Some common enzymes Conditions for optimum enzyme activity A! my! Every enzyme has optimal conditions under which it is l! most effective. a! s! • Temperature affects molecular motion. e – An enzyme’s optimal temperature produces the highest rate of contact between the reactants and the enzyme’s active site. – Most human enzymes work best at 35–40ºC. – But high temperature disrupts the structure • The optimal pH for most enzymes is near neutrality. catalase lactase http://mm.rcsb.org Sengupta 7 Bioenergetics Enzyme activity Effect of heat on enzyme activity Temperature pH Four Variables Enzyme Concentration Denaturing protein Substrate Concentration IF ACTIVE SITE CHANGES SHAPE: SUBSTRATE NO LONGER FITS Even if temperature lowered – enzyme cannot regain its correct shape Temperature Environmental Conditions can Cause Changes in Shape (Denaturing) 5- 35oC Increase in Activity 40oC -denatures RateReaction