Chapter 7 Bio PowerPoint PDF

2024-10-22 1 BIOLOGY 1 ELEVENTH EDITION 2 Chapter 7 Energy and Metabolism 3 © 2019 Cengage. All rights reserved. 2 Energy Conversion Cells obtain energy in many forms, and have mechanisms that convert energy from one form to another Radiant energy...

2024-10-22 1 BIOLOGY 1 ELEVENTH EDITION 2 Chapter 7 Energy and Metabolism 3 © 2019 Cengage. All rights reserved. 2 Energy Conversion Cells obtain energy in many forms, and have mechanisms that convert energy from one form to another Radiant energy is the ultimate source of energy for life – Photosynthetic organisms capture about 0.02% of the sun’s energy that reaches Earth, and convert it to chemical energy in bonds of organic molecules 3 7.1 Biological Work Matter: anything that has mass and takes up space Energy: the capacity to do work (change in state or motion of matter) – Expressed in units of work (kilojoules, kJ) or units of heat energy (kilocalories, kcal) – 1 kcal = 4.184 kJ – 4 Potential Energy and Kinetic Energy Potential energy: capacity to do work as a result of position or state Kinetic energy: energy of motion is used, work is performed 5 Organisms Carry Out Conversions Between Potential/Kinetic Energy Most actions involve a series of energy transformations that result from a conversion of energy between the potential and kinetic energy states. Chemical energy: potential energy stored in chemical bonds – Example: Chemical energy of food molecules is converted to mechanical energy in muscle cells – 6 7.2 The Laws of Thermodynamics Thermodynamics governs all activities of the universe, from cells to stars Biological systems are open systems that exchange energy with their surroundings 7 The First Law of Thermodynamics Energy cannot be created or destroyed Energy can be transferred or converted from one form to another, including conversions between matter and energy – The energy of any system plus its surroundings is constant – Organisms must capture energy from the environment and transform it to a form that can be used for biological work 8 The Second Law of Thermodynamics When energy is converted from one form to another, some usable energy (energy available to do work) is converted into heat that disperses into the surroundings – As a result, the amount of usable energy available to do work in the universe decreases over time (Entropy increases) 1  2024-10-22 Heat: the kinetic energy of randomly moving particles 9 Entropy The measure of the disorder or randomness of energy – Organized, usable energy has a low entropy – Disorganized energy, such as heat, has a high entropy No energy conversion is ever 100% efficient The total entropy of the universe always increases over time 10 7.3 Energy And Metabolism Metabolism: all chemical reactions taking place in an organism – Includes many intersecting chemical reactions Two main types: – Anabolism: pathways in which complex molecules are synthesized from simpler substances – Catabolism: pathways in which larger molecules are broken down into smaller ones – 11 Enthalpy is the Total Potential Energy of a System Every specific type of chemical bond has a certain amount of bond energy: the energy required to break that bond Enthalpy is equivalent to the total bond energy 12 Free Energy is Available to do Cell Work Free energy: the amount of energy available to do work under the conditions of a biochemical reaction Enthalpy (H), free energy (G), entropy (S); and absolute temperature (T) are related: H = G + TS As entropy increases, the amount of free energy decreases 13 Changes in Free Energy Although the total free energy of a system (G) can’t be measured, changes in free energy can be measured The rearranged equation can be used to predict whether a particular chemical reaction will release energy or require an input of energy: ΔG=ΔH−TΔS 14 Free Energy Decreases During an Exergonic Reaction Exergonic reaction: releases energy and is a “downhill” reaction, from higher to lower free energy ΔG is a negative number for exergonic reactions 15 Free Energy Increases During an Endergonic Reaction Endergonic reaction: a reaction in which there is a gain of free energy ΔG has a positive value: the free energy of the products is greater than the free energy of the reactants 2  2024-10-22 ΔG has a positive value: the free energy of the products is greater than the free energy of the reactants Requires an input of energy from the environment 16 17 Diffusion is an Exergonic Process Randomly moving particles diffuse down their own concentration gradient-no energy input required Concentration gradient: an orderly state with a region of higher concentration and another region of lower concentration – A cell must use energy to produce a concentration gradient 18 Free-Energy Changes and the Concentrations of Reactants/Products Free-energy changes in a chemical reaction depend on the difference in bond energies between reactants and products – Also depends on concentrations of both reactants and products A reaction that proceeds forward and in reverse at the same time eventually reaches dynamic equilibrium 19 Changes in Free Energy (cont’d.) If the reactants have much greater free energy than the products, most of the reactants are converted to products and vice-versa If the concentration of reactants is increased, the reaction will “shift to the right” and vice-versa – The reaction always shifts to reestablish equilibrium 20 Cells Drive Endergonic Reactions by Coupling Them Endergonic reactions are coupled to exergonic reactions In other words, reactions that require energy are often coupled reactions that release energy. – Coupled reactions: thermodynamically favorable exergonic reaction provides energy required to drive a thermodynamically unfavorable endergonic reaction – In a living cell the exergonic reaction often involves the breakdown of ATP 21 Coupled Reactions (cont’d.) Two reactions taken together are exergonic: (1) A → B ΔG = +20.9 kJ/mol (+5 kcal/mol) (2) C → D ΔG = −33.5 kJ/mol (−8 kcal/mol) Overall ΔG = −12.6 kJ/mol (−3 kcal/mol) Reactions are coupled if pathways are altered for a common intermediate link: (3) A + C → I ΔG = −8.4 kJ/mol (−2 kcal/mol) (4) I → B + D ΔG = −4.2 kJ/mol (−1 kcal/mol) Overall ΔG = −12.6 kJ/mol (−3 kcal/mol) 22 7.4 ATP, Energy Currency of the Cell Adenosine triphosphate (ATP): Nucleotide consisting of adenine, ribose, and three phosphate groups – The cell uses energy that is temporarily stored in ATP – Hydrolysis of ATP yields ADP and inorganic phosphate 23 ATP Donates Energy 3  2024-10-22 Hydrolysis of ATP can be coupled to endergonic reactions in cells, such as the formation of sucrose ATP + H2O → ADP + Pi ΔG = −32 kJ/mol (or −7.6 kcal/mol) glucose + fructose → sucrose + H2O ΔG = +27 kJ/mol (or +6.5 kcal/mol) glucose + fructose + ATP → sucrose + ADP + Pi ΔG = −5 kJ/mol (−1.2 kcal/mol) 24 ATP Donates Energy (cont’d.) The intermediate reaction in the formation of sucrose is a phosphorylation reaction: phosphate group is transferred to glucose to form glucose-P glucose + ATP → glucose-P + ADP glucose-P + fructose → sucrose + Pi 25 ATP Links Exergonic and Endergonic Reactions 26 The Cell Maintains a Very High Ratio of ATP to ADP A typical cell contains more than 10 ATP molecules for every ADP molecule – High levels of ATP makes its hydrolysis reaction more strongly exergonic, and more able to drive coupled endergonic reactions The cell cannot store large quantities of ATP – ATP is constantly used and replaced 27 7.5 Energy Transfer in Redox Reactions Energy is transferred through the transfer of electrons from one substance to another – Oxidation: substance loses electrons – Reduction: substance gains electrons Redox reactions often occur in a series of electron transfers – For cellular respiration, photosynthesis, and many other chemical processes 28 Electron Carriers Transfer Hydrogen Atoms Redox reactions in cells usually involve the transfer of a hydrogen atom – An electron, along with its energy, is transferred to an acceptor molecule such as nicotinamide adenine dinucleotide (NAD+), which is reduced to NADH XH2 + NAD+ → X + NADH + H+ 29 30 Electron Carriers (cont’d.) An electron progressively loses free energy as it is transferred from one acceptor to another – In cellular respiration, NADH transfers electrons to another molecule Energy is then transferred through a series of reactions that result in formation of ATP – NADP+ is not involved in ATP synthesis Electrons of NADPH are used to provide energy for photosynthesis 4  2024-10-22 31 Other Important Electron Carriers Flavin adenine dinucleotide (FAD): nucleotide that accepts hydrogen atoms and their electrons – Reduced form is FADH2 Cytochromes: proteins that contain iron – The iron component accepts electrons from hydrogen atoms, then transfers the electrons to some other compound 32 7.6 Enzymes Cells regulate rates of chemical reactions with enzymes, which increase speed of a chemical reaction without being consumed by the reaction – Example: Catalase has the highest known catalytic rate; it protects cells by destroying hydrogen peroxide (H2O2) – Most enzymes are proteins, but some types of RNA molecules also have catalytic activity 33 All Reactions Have a Required Energy of Activation Even a strongly exergonic reaction may be prevented from proceeding by the activation energy required to begin the reaction Energy of activation (EA) or activation energy: the energy required to break existing bonds and begin a reaction – – 34 35 An Enzyme Works By Forming an Enzyme–Substrate Complex An enzyme controls the reaction by forming an unstable intermediate complex with a substrate When the ES complex breaks up, the product is released – Enzyme molecule is free to form a new ES complex: enzyme + substrate(s) → ES complex ES complex → enzyme + product(s) 36 Active Sites Enzymes bind to active sites to position substrates close together to speed up the reaction – Induced fit: binding of substrate to enzyme causes a change in shape to enzyme Distorts the chemical bonds of the substrate – Proximity and orientation of reactants, plus strains in their chemical bonds, facilitate the breakage/formation of products 37 Enzymes are Specific Due to shape of active site and its relationship to the shape of the substrate Some are specific only to a certain chemical bond – Example: lipase splits ester linkages in many fats Scientists classify enzymes into six classes that catalyze similar reactions – Each class is divided into many subclasses 38 39 Many Enzymes Require Cofactors 5  2024-10-22 Some enzymes have two components: an apoenzyme and a cofactor – Neither alone has catalytic activity, enzyme functions only when the two combined Cofactors may be a specific metal ion – Iron, copper, zinc, and manganese all function as cofactors 40 Coenzymes Organic, nonpolypeptide compound that binds to the apoenzyme and serves as a cofactor – Most are carrier molecules: NADH, NADPH, and FADH2 transfer electrons ATP transfers phosphate groups Coenzyme A transfers groups derived from organic acids – Most vitamins are coenzymes or components of coenzymes 41 Each Enzyme Has an Optimal Temperature 42 Heat-Tolerant Archaea Certain archaea have enzymes that allow them to survive in extreme habitats 43 Each Enzyme has an Optimal pH Optimal pH for most human enzymes is 6 to 8 44 Enzymes in Metabolic Pathways Metabolic pathway: the product of one enzyme-controlled reaction serves as substrate for the next in series of reactions – Removal of intermediate and final products drives the sequence of reactions in a particular direction – Enzymes can bind to one another to form a multienzyme complex that transfers intermediates in the pathway from one active site to another 45 The Cell Regulates Enzymatic Activity Gene control: a specific gene directs synthesis of each type of enzyme – Gene may be switched on by a signal from a hormone or other signal molecule – Amounts of enzymes influence overall cell reaction rate 46 47 The Cell Regulates Enzymatic Activity (cont’d.) The product of one enzymatic reaction may control activity of another enzyme in a sequence of enzymatic reactions – When concentration of a product is low, the sequence of reactions proceeds rapidly – When concentration of a product is high, reactions stop 48 The Cell Regulates Enzymatic Activity (cont’d.) Feedback inhibition – Enzyme regulation in which the formation of a product inhibits an earlier reaction in the sequence 49 Removal of the allosteric inhibitor allows the enzyme to bind its substrates (enzyme is active) 6  2024-10-22 Removal of the allosteric inhibitor allows the enzyme to bind its substrates (enzyme is active) 50 Enzymes Are Inhibited by Certain Chemical Agents 51 Enzyme Inhibition (cont’d.) Irreversible inhibition: inhibitor permanently inactivates or destroys an enzyme when the inhibitor combines with one of the enzyme’s functional groups, either at the active site or elsewhere – Many poisons are irreversible enzyme inhibitors, such as mercury and lead, nerve gases, cyanide 52 Some Drugs are Enzyme Inhibitors Some drugs used to treat bacterial infections directly or indirectly inhibit bacterial enzyme activity – Example: sulfa drugs compete with PABA for the active site of the bacterial enzyme – Example: penicillin and related antibiotics irreversibly inhibit the bacterial enzyme transpeptidase Drug resistance is a growing problem 7