Chapter 6: Metabolism - Biology Textbook PDF

Because learning changes everything.® Biology Sylvia S. Mader...

Because learning changes everything.® Biology Sylvia S. Mader Michael Windelspecht Chapter 6 Metabolism: Energy & Enzymes Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. Outline  6.1 Cells and the Flow of Energy  6.2 Metabolic Reactions and Energy Transformations  6.3 Metabolic Pathways and Enzymes  6.4 Organelles and the Flow of Energy 2 6.1 Cells & Flow of Energy: Energy: ability to do work or bring about a change. Two forms of energy: a) Kinetic Energy: Energy of motion: Mechanical, water going over a waterfall b) Potential Energy: Stored energy: Chemical energy, the food we eat. Energy flows and does not cycle Two Laws of Thermodynamics: 1.The Law of conservation of Energy: Energy cannot be created or destroyed, it can be changed from one form to another. Ex. Photosynthesis 2.The Law of Entropy: Energy cannot be changed from one form to another without loss of usable energy. No process requiring a conversion of energy is ever 100% efficient. This energy transformation makes the universe less organized. Disorder is increasing in the universe.  heat CO2 sun H2O carbohydrate solar energy producer Organisms called producers use energy to create organized structure in biological molecules. Carbohydrate Metabolism As the moose walks it uses the potential energy stored in carbohydrates to kinetically power its muscles. ALL Living organisms depend on a constant supply of solar energy. 6-6 Copyright ©2019 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill  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. Similarly, the input of energy from photosynthesis (the sun) makes glucose from carbon dioxide and water. 7 Cells and Entropy 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) 8 b. 6.2 Metabolism and Energy Transformations Metabolism: is the sum of all the chemical reactions that occur in a cell. Free energy (delta G): amount of energy left to do work after a chemical reaction has occurred. ΔG = Free E of products - Free E of reactants  Exergonic Reactions – ΔG < 0, Spontaneous rxn Products have less free energy than reactants. Release energy.  Endergonic Reactions - ΔG > 0 , Nonspontaneous. Products have more free energy than reactants. Requires energy ΔG>0 Δ G < 0, Spontaneous TP: Energy currency for Cells ATP is unstable and has a high potential energy. P P P ATP - nucleotide formed of: * Adenine, ribose sugar (Adenosine) & 3 phosphate groups - supplies energy to do: * Chemical Work : synthesis of macromolecules * Transport Work: pump substances across the membrane 11 * Mechanical Work: muscles contraction, movement of cilia & flagella  ATP Cycle  ATP is not stored in cells.  ATP captures the energy released by exergonic reactions.  ATP acts as a carrier of chemical E to drive endergonic reactions.  Cell has 2 ways to couple ATP hydrolysis to an E-requiring rxn.: 1- ATP is used to energize a reactant 2- ATP can change the shape of a reactant. The ATP Cycle 2 Figure 6.3  Access the text alternative for slide images. 1 The ATP Cycle 4 Figure 6.3  Access the text alternative for slide images. 1 Coupled Reactions Muscle contraction occurs only when it is coupled to ATP breakdown ATP splits into ADP Release of ADP and 1 Myosin assumes its 2 and p , causing 3 p cause myosin to resting shape when myosin to change its again change shape It combines with ATP. shape and allowing it and pull against actin, to attach to actin. generating force and motion. actin P ADP ATP myosin During this cycle, chemical E is transferred to mechanical E & entropy increases. 15  6.3 Metabolic Pathways and Enzymes Reactions normally occur in a sequence. Metabolic pathway= Such linked reactions.  It 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 or Substrate 6-16 Copyright ©2019 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Enzyme Protein molecules function as catalysts. 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. 6-17 Copyright ©2019 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill  Enzyme-Substrate Complexes  Active site: part of the enzyme that complexes with substrate.  It causes the active site to change shape.  Induced fit Model: the enzyme is induced to undergo a slight change in shape to fit the substrate  After the reaction has been completed, the product is released and the active site returns to its original shape. Degradation vs. synthesis Degradation The substrate is broken down to smaller products. Synthesis The substrates are combined to produce a larger product.  Energy of Activation  Energy that must be added to cause molecules to react with one another.  EA prevents the molecules from spontaneously degrading within the cell.  Enzymes lower the energy of activation by bringing the substrates into contact, thus speeding up the reaction. Examples of Enzymes and their Substrates:  Factors Affecting Enzymatic Rate 1. Substrate Concentration: Enzyme activity increases with substrate concentration due to more frequent collisions between substrate molecules and the enzyme. 2. Temperature: Enzyme activity increases with temperature. Warmer temperatures cause more effective collisions between enzyme and substrate. However, hot temperatures can denature and destroy enzymes. 3. pH: Enzymes have an optimal pH at which the rate of reaction is highest. A change in pH can change the shape of an enzyme => lowering enzymatic speed. At extreme pHs, the enzyme denatures. Factors Affecting Enzymatic Rate (3) Siamese cats have a mutation that causes enzymes to be active only at cooler body temperatures, affecting coloration 6-23 Copyright ©2019 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill The Effect of Temperature on Rate of Reaction (product per unit of time) Rate of Reaction 0 10 20 30 40 50 60 Temperature C Body temperature of ectothermic Body temperature of endothermic animals animals limits rates of reactions. promotes rates of reactions 24 The Effect of pH on Rate of Reaction pepsin trypsin (product per unit of time) Rate of Reaction 0 1 2 3 4 5 6 7 8 9 10 11 12 pH 25  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 active site  Noncompetitive inhibition – the inhibitor does not bind at the active site, but at an allosteric site 27 Noncompetitive Inhibition of an Enzyme 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. 28 6.4 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;  OILRIG (oxidation is loss, reduction is gain). 6-29 Copyright ©2019 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Photosynthesis and Cellular Respiration sun Reduced Oxidized Oxidized Reduced 30  Photosynthesis in chloroplast Chloroplasts capture solar energy and use it to convert water and carbon dioxide to a carbohydrate. Hydrogen atoms are transferred from water to carbon dioxide as glucose forms. Carbon dioxide has been reduced and water oxidized. The energy is provided by solar energy.  The reduction of carbon dioxide to form a mole of glucose stores 686 kilocalories of energy in the chemical bonds of glucose. Involves the coenzyme NADP+ NADP+ + 2e + H+ NADPH  Living organisms can oxidize glucose in mitochondria.  Cellular Respiration in mitochondria Mitochondria oxidize carbohydrates and use the released energy to build ATP. Cellular respiration consumes oxygen and produces carbon dioxide. The equation is the opposite of the photosynthesis equation. Glucose has been oxidized (lost hydrogen atoms) and oxygen has been reduced (gained hydrogen atoms).  When oxygen gains hydrogen atoms, it becomes water. Cells oxidize glucose step by step.  The energy is stored and converted to ATP molecules.  Involves the coenzyme NAD+ NAD+ + 2e + H+ NADH 33