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Chapter 8: An introduction to Metabolism

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1 Chapter 8: An introduction to Metabolism

2 Start Your Engines Is a living organism an open or closed system?
Explain your answer.

3 Metabolism Metabolism in the living cell
Miniature factory where thousands of reactions or energy conversions occur Energy Free energy Energy in Biological systems ATP Enzymes Function Regulation

4 Explain the concept of energy coupling in the of biological system.
Starter. Explain the concept of energy coupling in the of biological system. (hint: think ATP)

5 Metabolism What is Metabolism
The totality of an organisms chemical reactions.

6 Metabolism Energy Conversion is not 100% Metabolism transforms matter and energy, subject to the laws of thermodynamics Energy can be transferred and transformed but NOT destroyed 2. Every energy transformation Increases the entropy in the universe.

7 Metabolic Pathways Metabolism is Controlled
Metabolism occurs in pathways sometimes with many steps. Begins w/ specific molecule, ends w/ product Each step catalyzed by specific enzyme Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting molecule Product

8 Proteins Amino Acids Metabolism Catabolic pathways
Complex molecules  simpler compounds Release energy Proteins Amino Acids

9 Metabolism Anabolic pathways
Build complicated molecules from simpler ones Consume energy

10 Energy can be converted from one form to another
On the platform, a diver has more potential energy. Diving converts potential energy to kinetic energy. Climbing up converts kinetic energy of muscle movement to potential energy. In the water, a diver has less potential energy. Figure 8.2 Kinetic Potential Chemical Thermal

11 Energy in a Biological System
Energy conversion Chemical energy

12 The Second Law of Thermodynamics
Spontaneous changes increase the entropy, or disorder, of the universe Heat co2 H2O + Energy Conversion is not 100%

13 Energy Living systems Increase entropy of the universe
Use energy to maintain order 50µm Figure 8.4

14 Free-Energy Change, G Determines if reaction occurs spontaneously

15 ∆Free energy= ∆(Enthalpy) – T∆(Entropy) Negative ∆G= Spontaneous
Change in free energy, ∆G during a biological process Related directly to the enthalpy (total energy of a system ∆H) change and the change in entropy ∆G = ∆H – T∆S ∆Free energy= ∆(Enthalpy) – T∆(Entropy) Negative ∆G= Spontaneous Positive ∆G = Requires energy

16 (a) Exergonic reaction: energy released
Net release of free E, spontaneous Figure 8.6 Reactants Products Energy Progress of the reaction Amount of energy released (∆G <0) Free energy (a) Exergonic reaction: energy released

17 (b) Endergonic reaction: energy required
Absorbs free E from surroundings, nonspontaneous Figure 8.6 Energy Products Amount of energy released (∆G>0) Reactants Progress of the reaction Free energy (b) Endergonic reaction: energy required

18 Energy in a Biological Systems
Maximum stability  system at equilibrium Chemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. . Diffusion. Molecules in a drop of dye diffuse until they are randomly dispersed. Gravitational motion. Objects move spontaneously from a higher altitude to a lower one. More free energy (higher G) Less stable Greater work capacity Less free energy (lower G) More stable Less work capacity In a spontaneously 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 (a) (b) (c) Figure 8.5 

19 Metabolic pathways as systems: Closed System
Reactions in a closed system eventually reach equilibrium ∆G < 0 ∆G = 0

20 Cells constant flow of materials in and out, do not reach equilibrium
Open System Cells constant flow of materials in and out, do not reach equilibrium ∆G < 0

21 Multi-Step Open System
Analogy for cellular respiration ∆G < 0 Holy Exergonic Reactions Batman!

22 ATP Cellular Energy Currency
(adenosine triphosphate) Cell’s Energy shuttle. ATP powers cellular work by coupling exergonic reactions to endergonic reactions Figure 8.8 O CH2 H OH N C HC NH2 Adenine Ribose Phosphate groups - CH

23 ATP E released from ATP when terminal phosphate bond is broken (hydrolysis) Figure 8.9 P Adenosine triphosphate (ATP) H2O + Energy Inorganic phosphate Adenosine diphosphate (ADP) P i

24 ATP Must look at total ∆G
ATP hydrolysis coupled to other reactions Endergonic reaction: ∆G is positive, reaction is not spontaneous ∆G = +3.4 kcal/mol Glu ∆G = kcal/mol ATP H2O + NH3 ADP NH2 Glutamic acid Ammonia Glutamine Exergonic reaction: ∆ G is negative, reaction is spontaneous P Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/mol

25 Cellular work powered by hydrolysis of ATP
(c) Chemical work: ATP phosphorylates key reactants P Membrane protein Motor protein P i Protein moved (a) Mechanical work: ATP phosphorylates motor proteins ATP (b) Transport work: ATP phosphorylates transport proteins Solute transported Glu NH3 NH2 + Reactants: Glutamic acid and ammonia Product (glutamine) made ADP

26 Regeneration of ATP Energy from Food!!
Catabolic pathways: ATP from ADP and phosphate (ATP Synthesis) ATP synthesis from ADP + P i requires energy ATP ADP + P i Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy yielding processes) ATP hydrolysis to ADP + P i yields energy Figure 8.12


28 Proteins, speed up metabolic reactions by lowering E barriers
Enzymes Proteins, speed up metabolic reactions by lowering E barriers Catalyst: speeds up a reaction w/o being consumed by the reaction Proximity

29 Enzymes Substrate Enzyme Reactant an enzyme acts on
Binds to substrate, forming enzyme-substrate complex Complex Substrate Enzyme

30 Enzymes Lower the EA Barrier
Activation energy, EA Initial amount of E needed to start a chemical reaction. Often in the form of heat Progress of the reaction Products Course of reaction without enzyme Reactants with enzyme EA EA with is lower ∆G is unaffected by enzyme Free energy Figure 8.15 Even w/ -∆G reaction may be too slow biologically

31 How Enzymes Work Active site
Region on enzyme where the substrate binds Figure 8.16 Substate Active site Enzyme (a)

32 Induced fit of substrate
substrate in positions that enhance catalysis Figure 8.16 (b) Enzyme- substrate complex Can be multiple active sites

33 Catalytic cycle of an enzyme
Conformational change Substrates Products Enzyme Enzyme-substrate complex 1 Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). 2 Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. 3 Active site (and R groups of its amino acids) can lower EA and speed up a reaction by • acting as a template for substrate orientation, • stressing the substrates and stabilizing the transition state, • providing a favorable microenvironment, • participating directly in the catalytic reaction. 4 Substrates are Converted into Products. 5 Products are Released. 1 6 Active site Is available for two new substrate Mole. Figure 8.17

34 (a) Optimal temperature for two enzymes
Enzymes have optimal conditions in which they function Figure 8.18 Optimal temperature for enzyme of thermophilic Rate of reaction 20 40 80 100 Temperature (Cº) (a) Optimal temperature for two enzymes typical human enzyme (heat-tolerant) bacteria Temp pH

35 Enzymes Cofactors Coenzymes Nonprotein enzyme helper Organic cofactors
Cu+, Mg2+, Mn2+ Coenzymes Organic cofactors NAD, FAD, vitamins

36 Enzyme Regulation Regulation of enzyme activity controls metabolism Cell’s metabolic pathways tightly regulated

37 Enzyme Regulation: Competitive inhibitors
Bind to active site, compete w/ substrate Figure 8.19 (b) Competitive inhibition A competitive inhibitor mimics the substrate, competing for the active site. Competitive inhibitor A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding

38 Enzyme regulation: Noncompetitive inhibitors
Bind to another part of enzyme, changing function Figure 8.19 A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Noncompetitive inhibitor (c) Noncompetitive inhibition

39 Enzyme Regulation: Allosteric
Protein’s function at one site is affected by binding of a regulatory molecule at another site Stabilized inactive form Allosteric activater stabilizes active from Allosteric enyzme with four subunits Active site (one of four) Regulatory site (one of four) Active form Activator Stabilized active form Allosteric inactivater stabilizes inactive form Inhibitor Inactive form Non- functional active site (a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again. Oscillation Figure 8.20

40 Enzyme regulation: Cooperativity
Cooperativity; allosteric regulation that amplifies enzyme activity Figure 8.20 Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation. Substrate Inactive form Stabilized active form (b) Cooperativity: another type of allosteric activation. Note that the inactive form shown on the left oscillates back and forth with the active form when the active form is not stabilized by substrate.

41 Enzyme Regulation: Feedback Inhibition
End product of metabolic pathway shuts down pathway Active site available Isoleucine used up by cell Feedback inhibition Isoleucine binds to allosteric site Active site of enzyme 1 no longer binds threonine; pathway is switched off Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Intermediate A Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 End product (isoleucine) Figure 8.21

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