Chapter 6 Energy, Enzymes, and Biological Reactions PDF
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The University of Texas at Dallas
Russell Hertz McMillan Benington
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This chapter in a biology textbook discusses energy, enzymes, and biological reactions, including topics such as thermodynamics, types of energy, and enzyme function. It covers fundamental concepts in biology for undergraduate students.
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of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm...
of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as Chapter 6 s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 Energy, Enzymes, and Biological o n Dr ntro OL Reactions BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6.1 Energy, Life, and Laws of Thermodynamics of of., iolo © Energy is defined as the capacity to do work xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er Energy exists in many different forms, including chemical, niv Pro rca od mm all n, electrical, thermal, and radiant energy (including light, gamma e U nt Sa o M Su as s a uc Th sta N t 01_ rays, and X-rays) 0 As ub cti 11. Energy can be converted from one form to another – in plants,. S du 23 n the radiant energy of sunlight is transformed into chemical o Dr ntro OL BI energy in the form of organic molecules h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Kinetic Energy and Potential Energy of of., iolo © All forms of energy can exist in one of two states (kinetic or xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. potential), which are interconvertible ers fes r, P ern er niv Pro rca od mm all n, Kinetic energy is the energy of an object in motion e U nt Sa o M Su as s a uc Th sta N t 01_ Examples: a falling rock, electricity, and light 0 As ub cti 11. Potential energy is stored energy. S du 23 o n Dr ntro OL Examples: a rock at the top of a hill, chemical energy, gravitational BI energy, and stored mechanical energy h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Energy Flow in Natural Systems of of., iolo © Thermodynamics is the study of energy and its xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. transformations ers fes r, P ern er niv Pro rca od mm all n, When discussing thermodynamics, scientists refer to a system, which e U nt Sa o M Su as s a uc Th sta N t 01_ is the object under study – everything outside a system is its surroundings 0 As ub cti 11.. S du 23 There are three types of systems: isolated, closed, and open o n systems Dr ntro OL BI a All living organisms are open systems h I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Systems in Thermodynamics of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. First Law of Thermodynamics of of., iolo © First law of thermodynamics xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er Energy can be transformed from one form to another, or transferred niv Pro rca od mm all n, from one place to another, but it cannot be created or destroyed e U nt Sa o M Su as s a uc Th sta N t 01_ Also called the principle of conservation of energy 0 As ub cti 11. In any process that involves energy change, the total amount. S du 23 n of energy in a system and its surroundings remains constant o Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Energy Flow from the Sun of of., iolo © For most organisms, the ultimate source of iStock.com/KenCanning xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. energy is the sun – plants capture kinetic energy ers fes r, P ern er niv Pro rca od mm of light and convert it to the chemical potential all n, energy of complex organic molecules e U nt Sa o M Su as s a uc Th sta N t 01_ Chemical potential energy stored in sugars and 0 As ub cti 11. other organic molecules is used for growth,. S du 23 n reproduction, and other work of living organisms o Dr ntro OL Hack_bsh/Shutterstock.com BI Eventually most of the solar energy absorbed by a green plants is converted into heat energy (which h is largely unusable by living organisms) and I radiated into space s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Second Law of Thermodynamics of of., iolo © Second law of thermodynamics xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er The total disorder (entropy) of a system and its surroundings always niv Pro rca od mm all n, increases (although the total energy in the universe does not change) e U nt Sa o M Su as s a uc Th sta N t 01_ Living organisms seem to decrease in entropy as they grow – 0 As ub cti 11. but when nutrients and waste products are considered, total. S du 23 energy remains constant and entropy increases o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6.2 Free Energy and Spontaneous Reactions of of., iolo © A spontaneous reaction is a chemical or physical reaction xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. that will occur without an input of energy ers fes r, P ern er niv Pro rca od mm all n, Two factors related to the first and second laws of e U nt Sa o M Su as s a uc Th sta N t 01_ thermodynamics must be considered to determine whether a 0 reaction is spontaneous: (1) the change in energy content of a As ub cti 11.. S du 23 system, and (2) its change in entropy o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Energy Content and Entropy Reactions tend to be spontaneous if the products have less potential of of., iolo © xa str , M -1 energy than the reactants ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er The potential energy in a system is its enthalpy (H) niv Pro rca od mm all n, Reactions that release energy are exothermic – the products have less e U nt Sa o M Su as s a uc Th sta N t 01_ potential energy than the reactants 0 As ub cti 11. Reactions that absorb energy are endothermic – the products have more. S du 23 potential energy than the reactants o n Dr ntro OL Reactions tend to be spontaneous when the products are less ordered BI (more random) than the reactants h a I Reactions tend to occur spontaneously if the entropy of the products is i greater than the entropy of the reactants s Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Change in Free Energy (1 of 2) of of., iolo © The portion of a system’s energy that is available to do work is xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. called free energy (G) ers fes r, P ern er niv Pro rca od mm all n, The change in free energy, ΔG can be calculated for any e U nt Sa o M Su as s a uc Th sta N t 01_ chemical reaction from the formula: 0 As ub cti 11.. S du 23 o n Dr ntro OL ΔH is the change in enthalpy BI a T is the absolute temperature in degrees Kelvin (K) h I ΔS is the change in entropy s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Change in Free Energy (2 of 2) of of., iolo © For a reaction to be spontaneous, ΔG must be negative xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er In some processes, such as the combustion of methane, the niv Pro rca od mm all n, large loss of potential energy, negative enthalpy (ΔH), e U nt Sa o M Su as s a uc Th sta N t 01_ dominates in making a reaction spontaneous 0 As ub cti 11. In other reactions, such as the melting of ice at room. S du 23 n temperature, a decrease in order (ΔS increases) dominates o Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Equilibrium Point (1 of 2) of of., iolo © In many spontaneous biological reactions reactants may not xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. convert completely to products even though the reactions have ers fes r, P ern er niv Pro rca od mm all n, a negative ΔG e U nt Sa o M Su as s a uc Th sta N t 01_ The reactions run in the direction of completion (toward 0 reactants or toward products) until they reach the equilibrium As ub cti 11.. S du 23 point – a state of balance between the opposing factors o n Dr ntro OL pushing the reaction in either direction BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Equilibrium Point (2 of 2) of of., iolo © As a system moves toward equilibrium, its free energy xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. becomes progressively lower and reaches its lowest point ers fes r, P ern er niv Pro rca od mm all n, when the system achieves equilibrium (ΔG = 0) e U nt Sa o M Su as s a uc Th sta N t 01_ To move away from equilibrium requires free energy and thus 0 will not be spontaneous As ub cti 11.. S du 23 n The more negative the ΔG, the further toward completion the o Dr ntro OL BI reaction will move before equilibrium is established h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Equilibrium Point of a Reaction of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Reversible Reactions of of., iolo © Many reactions have a ΔG that is near zero and are readily xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. reversible by adjusting the concentration of products and ers fes r, P ern er niv Pro rca od mm all n, reactants slightly e U nt Sa o M Su as s a uc Th sta N t 01_ Reversible reactions are written with a double arrow: 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Reactions in Living Organisms of of., iolo © Many reactions in living organisms never reach equilibrium xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. because living systems are open – the supply of reactants is ers fes r, P ern er niv Pro rca od mm all n, constant and products do not accumulate e U nt Sa o M Su as s a uc Th sta N t 01_ The ΔG of life is always negative – organisms constantly take in 0 energy-rich molecules and use them to do work As ub cti 11.. S du 23 Organisms reach equilibrium, ΔG = 0, only when they die o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Exergonic and Endergonic Reactions of of., iolo © Exergonic reaction xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er Reaction that releases free energy niv Pro rca od mm all n, ΔG is negative because the e U nt Sa o M Su products contain less free energy as s a uc Th sta N t 01_ than the reactants 0 As ub cti 11. Endergonic reaction. S du 23 o n Dr ntro OL Reactants must gain free energy BI from the surroundings to form the products ΔG is positive because the h a I products contain more free energy s i than the reactants Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Metabolic Pathways of of., iolo © A metabolic pathway is a series of reactions in which the products of one xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. reaction are used immediately as the reactants for the next reaction in the ers fes r, P ern er niv Pro rca od mm series all n, e U nt Sa o M Su In a catabolic pathway (or a single catabolic reaction) energy is as s a uc Th sta N t 01_ released by the breakdown of complex molecules to simpler compounds; 0 As ub cti 11. overall ΔG is negative. S du 23 o n Dr ntro OL In an anabolic pathway (or an anabolic reaction or biosynthetic BI reaction), energy is used to build complicated molecules from simpler h a ones; overall ΔG is positive I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6.3 Adenosine Triphosphate (ATP): Energy Currency of the Cell of of., iolo © The nucleotide adenosine triphosphate (ATP) consists of the xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. five-carbon sugar ribose linked to the nitrogenous base ers fes r, P ern er niv Pro rca od mm all n, adenine and a chain of three phosphate groups e U nt Sa o M Su as s a uc Th sta N t 01_ The negative charges of the phosphate groups repel each 0 other strongly, making the bonding arrangement unstable As ub cti 11.. S du 23 n Removal of one or two phosphate groups is a spontaneous o Dr ntro OL BI reaction that releases large amounts of free energy h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Hydrolysis of ATP ATP of of., iolo © The breakdown of ATP is a hydrolysis xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. reaction which results in the formation ers fes r, P ern er niv Pro rca od mm of adenosine diphosphate (ADP) and all n, a molecule of inorganic phosphate (Pi) e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI ADP can be hydrolyzed to adenosineh a I monophosphate (AMP) i s Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Energy Coupling, using ATP In the process of energy coupling, of of., iolo © xa str , M -1 when ATP is hydrolyzed, the terminal ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er phosphate group is transferred to a niv Pro rca od mm reactant molecule involved in an all n, e U nt Sa o M Su endergonic reaction as s a uc Th sta N t 01_ The addition of a phosphate group to a 0 As ub cti 11. molecule is called phosphorylation (the. S du 23 n modified molecule is phosphorylated) o Dr ntro OL BI Energy coupling requires an enzyme h a with a specific site that binds both ATP I and the reactant molecule to bring the i ATP and reactant molecule into close s association Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Regeneration of ATP The ATP/ADP Cycle of of., iolo © ATP synthesis from ADP and Pi is xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. an endergonic reaction that uses ers fes r, P ern er niv Pro rca od mm energy from the exergonic all n, breakdown of carbohydrates, e U nt Sa o M Su as s a uc Th sta N t 01_ proteins, and fats (food) 0 As ub cti 11. The continual hydrolysis and. S du 23 n resynthesis of ATP is called the o ATP/ADP cycle Dr ntro OL BI a Approximately 10 million ATP molecules are hydrolyzed and h I resynthesized each second in a s i typical cell Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6.4 Role of Enzymes in Biological Reactions of of., iolo © Even when a reaction is spontaneous (negative ΔG), the xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. reaction will not start unless a small amount of activation ers fes r, P ern er niv Pro rca od mm all n, energy (Ea) is added e U nt Sa o M Su as s a uc Th sta N t 01_ Activation energy makes bonds unstable and ready to be broken (the 0 transition state) As ub cti 11.. S du 23 Example: Activation energy is like the effort required to raise a rock o n Dr ntro OL over the rim of a depression and start it rolling downhill BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Activation Energy Enzymes Reduce Activation Energy of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzymes (1 of 2) of of., iolo © A catalyst is a chemical agent that accelerates (catalyzes) the xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. rate of a reaction without being changed by the reaction ers fes r, P ern er niv Pro rca od mm all n, The most common biological catalysts are proteins called e U nt Sa o M Su as s a uc Th sta N t 01_ enzymes, which increase the rate of reaction by lowering the 0 activation energy of the reaction As ub cti 11.. S du 23 n Enzymes do not alter the ΔG of the reaction o Dr ntro OL BI The free energy stays the same; the difference is in the path the reaction takes h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzymes (2 of 2) of of., iolo © The 3-D structure of a protein (its conformation) determines its xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. function – each enzyme has a specific protein structure that ers fes r, P ern er niv Pro rca od mm all n, catalyzes a specific reaction e U nt Sa o M Su as s a uc Th sta N t 01_ Cells have thousands of different enzymes, found in different 0 areas inside and outside of the cell As ub cti 11.. S du 23 n The name of an enzyme typically refers to its substrate or type o Dr ntro OL BI of reaction, and ends in –ase (e.g., proteinases) h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. An Enzyme and its Substrate of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzymatic Reactions (1 of 2) of of., iolo © In enzymatic reactions, an enzyme combines briefly with xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. reacting molecules and is released unchanged when the ers fes r, P ern er niv Pro rca od mm all n, reaction is complete e U nt Sa o M Su as s a uc Th sta N t 01_ The reactant that an enzyme acts on is called the substrate 0 As ub cti 11. Each type of enzyme catalyzes the reaction of a single type of. S du 23 n substrate molecule or group of closely related molecules o Dr ntro OL BI (enzyme specificity) h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzymatic Reactions (2 of 2) of of., iolo © The substrate interacts with a small pocket or groove in the xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. enzyme molecule, called the active site ers fes r, P ern er niv Pro rca od mm all n, When the substrate binds at the active site, both enzyme and e U nt Sa o M Su as s a uc Th sta N t 01_ substrate molecules are distorted – this makes the chemical 0 bonds in the substrate ready for reaction (induced fit) As ub cti 11.. S du 23 n Once an enzyme-substrate complex is formed, catalysis occurs o Dr ntro OL BI – the substrate is converted into one or more products h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Catalytic Cycle of Enzymes of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Cofactors and Coenzymes of of., iolo © Many enzymes require a cofactor, a nonprotein group that xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. binds to the enzyme, for catalytic activity ers fes r, P ern er niv Pro rca od mm all n, Some are metallic ions, including iron, copper, magnesium, zinc, and e U nt Sa o M Su as s a uc Th sta N t 01_ manganese 0 As ub cti 11. Other cofactors are small organic molecules (coenzymes). S du 23 which are often derived from vitamins o n Dr ntro OL BI Some coenzymes bind loosely to enzymes h a Others (prosthetic groups) bind tightly I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzymes Stabilize the Transition State of of., iolo © Enzymes stabilize the transition state through three major xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. mechanisms ers fes r, P ern er niv Pro rca od mm all n, Bringing the reacting molecules together e U nt Sa o M Su as s a uc Th sta N t 01_ Exposing the reactant molecules to altered charge environments that 0 As ub cti 11. promote catalysis. S du 23 n Changing the shape of the substrate molecules o Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6.5 Factors That Affect Enzyme Activity of of., iolo © Changes in concentration of substrate and other molecules xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. that bind to enzymes can alter enzyme activity ers fes r, P ern er niv Pro rca od mm all n, Control mechanisms modify enzyme activity, adjusting reaction e U nt Sa o M Su as s a uc Th sta N t 01_ rates to meet a cell’s requirements for chemical products 0 As ub cti 11. Changes in temperature and pH can have a significant effect. S du 23 n on enzyme activity o Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzyme and Substrate Concentrations of of., iolo © In the presence of excess substrate, the rate of catalysis is xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. proportional to the amount of enzyme ers fes r, P ern er niv Pro rca od mm all n, When enzyme concentration is kept constant and substrate e U nt Sa o M Su as s a uc Th sta N t 01_ concentration increases, the rate of catalysis increases until enzyme molecules are cycling as rapidly as possible 0 As ub cti 11.. S du 23 When enzymes are saturated with substrate, further increases o n Dr ntro OL in substrate concentration have no effect on reaction rate BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzyme Concentration of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzyme Inhibitors Competitive Inhibitors Enzyme inhibitors of of., iolo © are nonsubstrate xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. molecules that bind ers fes r, P ern er niv Pro rca od mm all n, to an enzyme and e U nt Sa o M Su as decrease its activity s a uc Th sta N t 01_ 0 Competitive As ub cti 11.. S du 23 inhibition o n Dr ntro OL BI Inhibitors bind to the a active site, blocking access for the normal h I substrate – slowing or s i stopping the reaction Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Enzyme Regulation of of., iolo © Cells adjust enzyme activity upward or downward to meet their xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. needs for reaction products ers fes r, P ern er niv Pro rca od mm all n, Several mechanisms regulate enzymes e U nt Sa o M Su as s a uc Th sta N t 01_ Competitive inhibition 0 As ub cti 11. Allosteric regulation. S du 23 o n Dr ntro OL Covalent modification of enzyme structure by the addition or removal BI of chemical groups h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Regulation by Inhibitors of of., iolo © Many molecules are synthesized by one enzyme and broken xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. down by another – the cell regulates enzyme activity so both ers fes r, P ern er niv Pro rca od mm all n, are not active at the same time e U nt Sa o M Su as s a uc Th sta N t 01_ Many enzymes are regulated by inhibitors that work either 0 competitively or noncompetitively in reversible inhibition As ub cti 11.. S du 23 n Control by inhibitors changes enzyme activity precisely to meet o Dr ntro OL BI the needs of the cell for the products of the reaction catalyzed a by the enzyme h I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Allosteric Regulation (1 of 5) of of., iolo © In allosteric regulation, enzyme activity is controlled by the xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. reversible binding of a regulatory molecule to the allosteric ers fes r, P ern er niv Pro rca od mm all n, site, a location on the enzyme outside the active site e U nt Sa o M Su as s a uc Th sta N t 01_ Enzymes controlled by allosteric regulation typically have two 0 alternate conformations: As ub cti 11.. S du 23 n In the high-affinity state (active form), the enzyme binds strongly to its o substrate Dr ntro OL BI h a In the low-affinity state (inactive form), the enzyme binds the substrate I weakly or not at all i s Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Allosteric Regulation (2 of 5) of of., iolo © Binding an allosteric activator induces the high-affinity state xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. and increases enzyme activity – an allosteric inhibitor ers fes r, P ern er niv Pro rca od mm all n, induces the low-affinity state and decreases enzyme activity e U nt Sa o M Su as s a uc Th sta N t 01_ Excess accumulation of a product often inhibits the enzymatic 0 reaction producing it (feedback inhibition or end-product As ub cti 11.. S du 23 inhibition) o n Dr ntro OL BI Example: The amino acid isoleucine is an allosteric inhibitor of the a biochemical pathway that makes isoleucine from threonine h I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Allosteric Regulation (3 of 5) of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Allosteric Regulation (4 of 5) of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Allosteric Regulation (5 of 5) of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Regulation by Chemical Modification of of., iolo © Many enzymes are regulated by chemical linkage to ions, xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. functional groups, or other molecules that induce changes in ers fes r, P ern er niv Pro rca od mm all n, the enzyme that increase or decrease its activity e U nt Sa o M Su as s a uc Th sta N t 01_ Example: 0 As ub cti 11. Phosphorylation by protein kinases may activate or deactivate a. S du 23 n particular enzyme o Dr ntro OL BI Dephosphorylation by protein phosphatases reverses the effects of a phosphorylation h I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Effects of pH of of., iolo © Each enzyme has an optimal pH at which it operates at peak xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. efficiency – the rate of reaction decreases on either side of this ers fes r, P ern er niv Pro rca od mm all n, pH optimum e U nt Sa o M Su as s a uc Th sta N t 01_ An enzyme’s dependence on pH typically is due to ionizable 0 amino acids – change in pH modifies the conformation of the As ub cti 11.. S du 23 protein and denatures the enzyme o n Dr ntro OL BI Most enzymes have an optimum of about pH 7; pepsin, a a protein-digesting enzyme secreted in the stomach, has an h I optimum of pH 1.5 s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Effects of pH on Enzymes of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Effects of Temperature of of., iolo © Temperature affects all chemical reactions xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er As temperature rises, the rate of chemical reactions increases niv Pro rca od mm all n, Temperature affects all proteins, including enzymes e U nt Sa o M Su as s a uc Th sta N t 01_ As temperature rises, kinetic motion increases – eventually hydrogen 0 As ub cti 11. bonds break and the enzyme denatures. S du 23 o n Dr ntro OL The two effects act in opposition to each other to produce BI characteristic changes in the rate of enzymatic catalysis h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Effects of Temperature on Enzymes of of., iolo © xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. ers fes r, P ern er niv Pro rca od mm all n, e U nt Sa o M Su as s a uc Th sta N t 01_ 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6.6 RNA-Based Biological Catalysts: Ribozymes of of., iolo © Ribozymes are a group of RNA molecules that accelerate the xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. rate of certain biological reactions without being changed by ers fes r, P ern er niv Pro rca od mm all n, the reactions e U nt Sa o M Su as s a uc Th sta N t 01_ Some ribozymes catalyze the cutting and splicing reactions 0 that remove surplus segments from RNA molecules As ub cti 11.. S du 23 n Ribozymes in ribosomes catalyze the linkage of amino acids in o Dr ntro OL BI protein synthesis h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. RNA World of of., iolo © The earliest forms of life might have inhabited an “RNA world” xa str , M -1 ity sor h.D B 24 Te In MS gy t D tio.Sc. in which neither DNA nor proteins played critical roles ers fes r, P ern er niv Pro rca od mm all n, Ribozymes could have acted as both enzymes and e U nt Sa o M Su as s a uc Th sta N t 01_ informational molecules when cellular life first appeared 0 As ub cti 11.. S du 23 o n Dr ntro OL BI h a I s i Russell, Biology: The Dynamic Science, 5th edition. © 2021 Cengage. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
