An Introduction to Metabolism 6 An Introduction to Metabolism

Concept 6.1: An organism’s metabolism transforms matter and energy © 2014 Pearson Education, Inc. 2

Enzyme 1 Enzyme 2 Enzyme 3 Starting molecule A B C D Product Figure 6.UN01 Enzyme 1 Enzyme 2 Enzyme 3 Starting molecule A B C D Product Reaction 1 Reaction 2 Reaction 3 Figure 6.UN01 In-text figure, metabolic pathway schematic, p. 116 3

Catabolic pathways Anabolic pathways © 2014 Pearson Education, Inc. 4

A diver has more potential energy on the platform. Figure 6.2 Diving converts potential energy to kinetic energy. A diver has more potential energy on the platform. Figure 6.2 Transformations between potential and kinetic energy Climbing up converts the kinetic energy of muscle movement to potential energy. A diver has less potential energy in the water. 5

(a) First law of thermodynamics (b) Second law of thermodynamics Figure 6.3 Heat Chemical energy Figure 6.3 The two laws of thermodynamics (a) First law of thermodynamics (b) Second law of thermodynamics 6

Free-Energy Change (G), Stability, and Equilibrium A living system’s free energy © 2014 Pearson Education, Inc. 7

The change in free energy (∆G) is the difference between ∆G = Gfinal state – Ginitial state © 2014 Pearson Education, Inc. 8

More free energy (higher G) Less stable Greater work capacity Figure 6.5 More free energy (higher G) Less stable Greater work capacity In a spontaneous change The free energy of the system decreases (G  0) The system becomes more stable The released free energy can be harnessed to do work Figure 6.5 The relationship of free energy to stability, work capacity, and spontaneous change Less free energy (lower G) More stable Less work capacity (a) Gravitational motion (b) Diffusion (c) Chemical reaction 9

Exergonic and Endergonic Reactions in Metabolism An exergonic reaction © 2014 Pearson Education, Inc. 10

Amount of energy released (G  0) Figure 6.6a (a) Exergonic reaction: energy released, spontaneous Reactants Amount of energy released (G  0) Energy Free energy Products Figure 6.6a Free energy changes (ΔG) in exergonic and endergonic reactions (part 1: exergonic) Progress of the reaction 11

Amount of energy required (G  0) Figure 6.6b (b) Endergonic reaction: energy required, nonspontaneous Products Amount of energy required (G  0) Energy Free energy Reactants Figure 6.6b Free energy changes (ΔG) in exergonic and endergonic reactions (part 2: endergonic) Progress of the reaction 12

An endergonic reaction © 2014 Pearson Education, Inc. 13

The Structure and Hydrolysis of ATP ATP (adenosine triphosphate) composed of © 2014 Pearson Education, Inc. 14

(a) The structure of ATP Figure 6.8 Adenine Phosphate groups Ribose (a) The structure of ATP Adenosine triphosphate (ATP) Figure 6.8 The structure and hydrolysis of adenosine triphosphate (ATP) Energy Inorganic phosphate Adenosine diphosphate (ADP) (b) The hydrolysis of ATP 15

Protein and vesicle moved Figure 6.10 Transport protein Solute Solute transported (a) Transport work: ATP phosphorylates transport proteins. Vesicle Cytoskeletal track Figure 6.10 How ATP drives transport and mechanical work Motor protein Protein and vesicle moved (b) Mechanical work: ATP binds noncovalently to motor proteins and then is hydrolyzed. 16

Concept 6.4: Enzymes speed up metabolic reactions by lowering energy barriers An enzyme © 2014 Pearson Education, Inc. 17

Sucrose (C12H22O11) Glucose (C6H12O6) Fructose (C6H12O6) Figure 6.UN02 Sucrase Sucrose (C12H22O11) Glucose (C6H12O6) Fructose (C6H12O6) Figure 6.UN02 In-text figure, hydrolysis of sucrose, p. 125 18

Progress of the reaction Figure 6.12 A B C D Transition state A B EA Free energy C D Reactants A B Figure 6.12 Energy profile of an exergonic reaction G  0 C D Products Progress of the reaction 19

How Enzymes Speed Up Reactions Enzymes do not affect the change in free energy (∆G); Animation: How Enzymes Work © 2014 Pearson Education, Inc. 20

Progress of the reaction Figure 6.13 Course of reaction without enzyme EA without enzyme EA with enzyme is lower Reactants Free energy Course of reaction with enzyme G is unaffected by enzyme Figure 6.13 The effect of an enzyme on activation energy Products Progress of the reaction 21

Substrate Specificity of Enzymes the substrate enzyme-substrate complex active site - © 2014 Pearson Education, Inc. 22

Substrate Active site Enzyme Enzyme-substrate complex Figure 6.14 Figure 6.14 Induced fit between an enzyme and its substrate Enzyme Enzyme-substrate complex 23

2 Substrates are held in active site by weak interactions. 1 Figure 6.15-4 2 Substrates are held in active site by weak interactions. 1 Substrates enter active site. Substrates Enzyme-substrate complex Active site is available for new substrates. 5 Figure 6.15-4 The active site and catalytic cycle of an enzyme (step 5) Enzyme Products are released. 4 3 Substrates are converted to products. Products 24

Effects of Local Conditions on Enzyme Activity © 2014 Pearson Education, Inc. 25

Optimal temperature for typical human enzyme (37C) Figure 6.16 Optimal temperature for typical human enzyme (37C) Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria (77C) Rate of reaction 20 40 60 80 100 120 Temperature (C) (a) Optimal temperature for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) Figure 6.16 Environmental factors affecting enzyme activity Rate of reaction 1 2 3 4 5 6 7 8 9 10 pH (b) Optimal pH for two enzymes 26

Cofactors Cofactors coenzymes Some coenzymes are vitamins 27 © 2014 Pearson Education, Inc. 27

Enzyme Inhibitors Competitive inhibitors Noncompetitive inhibitors 28 © 2014 Pearson Education, Inc. 28

(b) Competitive inhibition (c) Noncompetitive inhibition Figure 6.17 (a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition Substrate Active site Competitive inhibitor Enzyme Figure 6.17 Inhibition of enzyme activity Noncompetitive inhibitor 29

Allosteric Regulation of Enzymes © 2014 Pearson Education, Inc. 30

(a) Allosteric activators and inhibitors Figure 6.18 (a) Allosteric activators and inhibitors (b) Cooperativity: another type of allosteric activation Allosteric enzyme with four subunits Active site (one of four) Substrate Regulatory site (one of four) Activator Active form Stabilized active form Inactive form Stabilized active form Oscillation Figure 6.18 Allosteric regulation of enzyme activity Non- functional active site Inhibitor Inactive form Stabilized inactive form 31

Feedback Inhibition In feedback inhibition, 32 © 2014 Pearson Education, Inc. 32

End product (isoleucine) Figure 6.19 Active site available Threonine in active site Enzyme 1 (threonine deaminase) Isoleucine used up by cell Intermediate A Feedback inhibition Enzyme 2 Intermediate B Enzyme 3 Intermediate C Isoleucine binds to allosteric site. Figure 6.19 Feedback inhibition in isoleucine synthesis Enzyme 4 Intermediate D Enzyme 5 End product (isoleucine) 33