BIOL 1000: Chapter 6 Metabolism - Energy and Enzymes PDF

Ch. 6: Metabolism: Energy and Enzymes 6.1 Cells and the Flow of Energy Energy – The ability to do work or bring about a change – Kinetic energy Energy of motion Mechanical – Potential energy Stored energy – Chemical energy...

Ch. 6: Metabolism: Energy and Enzymes 6.1 Cells and the Flow of Energy Energy – The ability to do work or bring about a change – Kinetic energy Energy of motion Mechanical – Potential energy Stored energy – Chemical energy 1  Flow of Energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. solar energy heat heat heat Chemical energy Mechanical energy 2  Two Laws of Thermodynamics First law: – Law of conservation of energy – Energy cannot be created or destroyed, but can be changed from one form to another Second law: – Law of entropy When energy is changed from one form to another, there is a loss of energy that is available to do work. No process requiring a conversion of energy is ever 100% efficient. – The majority of energy is lost as dissipated heat. 3  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. heat CO2 sun H2O carbohydrate solar energy producer Two Laws of Thermodynamics Law of Conservation of Energy Energy cannot be created or destroyed, but can be changed from one form to another. Photosynthesizing leaves capture solar energy. Some energy is used to form carbohydrates from carbon dioxide and water. Much of the energy dissipates as heat. Law of Entropy When energy is changed from one form to another, there is a loss of energy that is available to do work. No process requiring a conversion of energy is ever 100% efficient. The majority of energy is lost as dissipated heat. 5  Cells and Entropy The processes occurring in cells are energy transformations. Every process in cells increases the total entropy in the universe. Therefore, less energy is available to do useful work. Example – Glucose tends to break apart into carbon dioxide and water over time. Glucose is more organized and less stable than its breakdown products. Compare this to a neat room, which is more organized but less stable than a messy room. Energy is required to make a messy room more neat. Similarly, the input of energy from photosynthesis (the sun) makes glucose from carbon dioxide and water. Organisms called producers use energy to create organized structure in biological molecules. Organisms that consume producers can use this potential energy to drive their own processes. Living organisms depend on a constant supply of solar energy. 6  Cells and Entropy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O C6H12O6 CO2 Glucose Carbon dioxide and water more organized kinetic less organized more potential energy energy less potential energy less stable (entropy) more stable (entropy) a. H+ H+ channel protein H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Unequal distribution Equal distribution of hydrogen ions of hydrogen ions more organized less organized more potential energy less potential energy less stable (entropy) more stable (entropy) 7 b.  What is the ‘work’ of the cell? What kinds of reactions or activities does the cell do that may need E? What form is the E that a cell uses to do work? Metabolic Reactions and Energy Transformations Metabolism – Sum of cellular chemical reactions in cell – Reactants participate in a reaction – Products form as result of a reaction Free energy is the amount of energy available to perform work – Exergonic Reactions - Products have less free energy than reactants (release energy) – Endergonic Reactions - Products have more free energy than reactants (require energy input) 9  ATP: Energy for Cells Adenosine triphosphate (ATP) – High energy compound used to drive metabolic reactions – Constantly being generated from adenosine diphosphate (ADP) Composed of: – Adenine, ribose (together = adenosine), and three phosphate groups Coupled reactions – Energy released by an exergonic reaction captured in ATP – ATP is used to drive an endergonic reaction 10  The ATP Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. adenosine triphosphate ATP is unstable and has a high potential energy. P P P ATP 11 Two Laws of Thermodynamics Law of Conservation of Energy Energy cannot be created or destroyed, but can be changed from one form to another. Photosynthesizing leaves capture solar energy. Some energy is used to form carbohydrates from carbon dioxide and water. Much of the energy dissipates as heat. Law of Entropy When energy is changed from one form to another, there is a loss of energy that is available to do work. No process requiring a conversion of energy is ever 100% efficient. The majority of energy is lost as dissipated heat. 12 Parts of a General Chemical Reaction 6.3 Metabolic Pathways and Enzymes Reactions usually occur in a sequence – Products of an earlier reaction become reactants of a later reaction – Such linked reactions form a metabolic pathway Begins with a particular reactant, proceeds through several intermediates, and terminates with a particular end product A➔B ➔C ➔D ➔E ➔F➔G “A” is Initial B, C, D, E, and F “G” is End Reactant are Intermediates Product 14  6.3 Metabolic Pathways and Enzymes Enzyme – Protein molecules that function as catalysts – Enzymes can be reused over and over again – Anything that can affect a protein can affect an enzyme (temp, pH, etc) – The reactants of an enzymatically catalyzed reaction are called substrates – Each enzyme accelerates a specific reaction – Each reaction in a metabolic pathway requires a unique and specific enzyme – The end product will not be formed unless ALL enzymes in the pathway are present and functional In the pathway below in order to get to product G the cell must go through the complete pathway E1 E2 E3 E4 E5 E6 A➔ B ➔ C ➔ D ➔ E ➔ F ➔ G 15  Why do cells need Enzymes? Energy of Activation Molecules frequently do not react with one another unless they are activated in some way – Energy must be added to at least one reactant to initiate the reaction Energy of activation Enzyme Operation: – Enzymes operate by lowering the energy of activation – Accomplished by bringing substrates into contact with one another 16 Energy of Activation (E sub a) Figure 6.6 Access the text alternative for slide images. 17 Enzymatic Actions Figure 6.5 Access the text alternative for slide images. 18  Enzyme-Substrate Complex The active site complexes with the substrates – Causes the active site to change shape – Shape change forces substrates together, initiating bond – Induced fit model Enzyme is induced to undergo a slight alteration to achieve optimum fit for the substrates 19  Cofactors at Active Site Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cofactor active site substrate a. b. 20  Factors Affecting Enzymatic Speed Substrate concentration – Enzyme activity increases with substrate concentration due to more frequent collisions between substrate molecules and the enzyme Temperature – Enzyme activity increases with temperature – Warmer temperatures cause more effective collisions between enzyme and substrate – However, hot temperatures can denature and destroy enzymes pH – Most enzymes are optimized for a particular pH 21 The Effect of pH on Rate of Reaction Figure 6.7 22 Enzyme Cofactors and Coenzymes Cells can regulate the presence/absence of an enzyme. Cells can regulate the concentration of an enzyme. Cells can activate or deactivate some enzymes. Enzyme cofactors Molecules required to activate enzyme. – FAD and NAD+ and NADP + are cofactors, the first two in cellular respiration, the third in photosynthesis. Coenzymes are nonprotein organic molecules. Vitamins are small, organic compounds required in the diet for the synthesis of coenzymes. 23  Enzyme Inhibition A substance known as an inhibitor binds to an enzyme and decreases its activity. Competitive inhibition – The substrate and the inhibitor are both able to bind to the active site and they compete with one another. The product forms only when the substrate binds to the active site. Noncompetitive inhibition – The inhibitor does not bind at the active site, but at an allosteric (allo means “other”) site. A change in shape initiated by an inhibitor binding to the allosteric site changes the shape of the active site, making it unable to bind to its substrate. 24 Enzyme Regulation: Negative Feedback Inhibition Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A E allosteric site 1 enzymes E E E E E F 1 2 3 4 5 substrates A B C D E (end product) 1 Metabolic pathway produces F, the end product. F active site E (end 1 product) 2 F binds to allosteric site and the active site of E1 changes shape. F A E (end 1 product) 3 A cannot bind to E1; the enzyme has been inhibited by F. 25  6.4 Oxidation-Reduction Reactions and Metabolism Oxidation-reduction (redox) reactions: Electrons pass from one molecule to another. Oxidation – loss of an electron. Reduction – gain of an electron. Both take place at the same time. One molecule (or atom) accepts the electron given up by the other. Example: In the production of NaCl, sodium is oxidized and chlorine is reduced; OIL RIG (oxidation is loss, reduction is gain). 26  Formation of Sodium Chloride Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Na Cl sodium atom (Na) chlorine atom (Cl) 27 Photosynthesis and Cellular Respiration Photosynthesis 6 CO2 C6 H12 O6 6 H2 O 6O2 carbon + + energy → + water glucose oxygen dioxide Cellular Respiration The overall equation for cellular respiration is opposite to that for photosynthesis: C6 H12 O6 6 CO2 6 O2 6 H2 O + → carbon + + energy glucose oxygen water dioxide 28