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Ch 8 Cellular Metabolism How cells utilize energy.

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Presentation on theme: "Ch 8 Cellular Metabolism How cells utilize energy."— Presentation transcript:

1 Ch 8 Cellular Metabolism How cells utilize energy

2 LE 8-2 On the platform, the 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, the diver has less potential energy.

3 LE 8-3 Chemical energy Heat CO 2 First law of thermodynamicsSecond law of thermodynamics H2OH2O

4 The First Law of Thermodynamics –Energy cannot be created or destroyed –Energy can be transferred and transformed Principle of conservation of energy

5 The Second Law of Thermodynamics Every energy transfer or transformation increases the entropy (disorder) of the universe Because some energy is lost as heat (unusable)

6 Metabolism – an organism’s (or cell’s) total chemical reactions Name a common cellular reaction. Two kinds of reactions: Catabolism (catabolic rxn) Breakdown of a larger molecule into smaller lower energy products Releases of energy Exergonic rxn Anabolism (anabolic rxn) Synthesis of larger high energy molecules from lower energy reactants Requires input of energy Endergonic reactions

7 LE 8-12 P i ADP Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy- yielding processes) ATP + Cellular energy used for: transport (across membranes) mechanical work (motility, contraction) enzymatic activity (catalysis of reactions)

8 Catabolic rxn C 6 H 12 O 6 + 6O 2 ----> 6CO 2 + 6H 2 O + ATP glucose Exergonic Anabolic rxn 6CO 2 + 6H 2 O ----> C 6 H 12 O 6 + 6O 2 glucose Endergonic Light Examples

9 Biological rxns -Catalyzed by enzymes -Often arranged in multiple steps called pathways

10 LE 8-UN141 Enzyme 1 AB Reaction 1 Enzyme 2 C Reaction 2 Enzyme 3 D Reaction 3 Product Starting molecule Enzymatic Pathway

11 Enzymes Biological catalysts Increase rate of reactions by lowering activation energy (E A ) Spontaneous reactions can take a long time! Need enzymes to speed reactions for cell survival

12 Activation Energy (E A ) Needed to destabilize bonds of reactants

13 LE 8-14 Transition state CD A B EAEA Products CD A B  G < O Progress of the reaction Reactants C D A B Free energy Could raise temp. to break bonds

14 Why don’t cells rely on increases in temperature to break bonds? Denaturation of proteins and damage to the cell.

15 LE 8-15 Course of reaction without enzyme E A without enzyme  G is unaffected by enzyme Progress of the reaction Free energy E A with enzyme is lower Course of reaction with enzyme Reactants Products

16 LE 8-13 Sucrose C 12 H 22 O 11 Glucose C 6 H 12 O 6 Fructose C 6 H 12 O 6 Example:

17 Structure & Function of Enzyme DRAW Enzymes bind substrate molecules (the reactant) Substrates bind to active site on enzyme Binding induces conformational change in enzyme--better ”fit” for substrate Active sites are highly specific and discriminatory i.e. sucrase does not accept lactose

18 LE 8-16 Substrate Active site Enzyme Enzyme-substrate complex

19 How does enzyme lower activation energy of reaction? –Orients substrates for optimal interaction –Strains substrate bonds –Provides a favorable microenvironment -Covalently bonds to the substrate

20 LE 8-17 Enzyme-substrate complex Substrates Enzyme Products Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. Active site (and R groups of its amino acids) can lower E A 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. Substrates are converted into products. Products are released. Active site is available for two new substrate molecules.

21 How do we know when a reaction is exergonic or endergonic? Measure the system’s ability to perform work (usable energy) at uniform temperature and pressure. Change in Gibbs free energy (G)  G=  H-T  S Where  H= change in total energy of the system, or enthalpy T=absolute temperature in Kelvin ( o C+273)  S =change in entropy (a measure of disorder)

22 Another way to think about the state of energy in a cell is before and after a particular reaction occurs  G = G final state - G initial state If the reaction gives final products that have less energy than the initial reactants, is  G negative or positive? The reverse? When  G < 0, the reaction is exergonic and spontaneous. When  G > 0, the reaction is endergonic and not spontaneous. (products) (reactants)

23 LE 8-6a Reactants Energy Products Progress of the reaction Amount of energy released (  G < 0) Free energy Exergonic reaction: energy released Catabolic rxn C 6 H 12 O 6 + 6O 2 ----> 6CO 2 + 6H 2 O + ATP glucose

24 LE 8-6b Reactants Energy Products Progress of the reaction Amount of energy required (  G > 0) Free energy Endergonic reaction: energy required Anabolic rxn 6CO 2 + 6H 2 O ----> C 6 H 12 O 6 + 6O 2 glucose Light

25 Relationship among Free Energy, Instability, and Equilibrium Free energy: – a measure of a system’s instability, its tendency to change to a more stable state During a spontaneous change –free energy decreases and the stability of a system increases Equilibrium is a state of maximum stability (  G=0) If the metabolism of a cell is at equilibrium, what has occurred? RIP

26 LE 8-12 P i ADP Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy- yielding processes) ATP + Cellular energy used for: transport (across membranes) mechanical work (motility, contraction) enzymatic activity (catalysis of reactions)

27 ATP structure ATP –adenosine triphosphate cellular energy carrier

28 LE 8-8 Phosphate groups Ribose (sugar) Adenine (base) ATP structure Adenosine triphosphate Cellular energy currency   

29 LE 8-9 Adenosine triphosphate (ATP) Energy PP P PP P i Adenosine diphosphate (ADP) Inorganic phosphate H2OH2O + +

30 Terminal phosphate bond (ATP--> ADP + P i ) –Hydrolysis of “high energy” phosphate bond Energy is released (exergonic) ADP lower energy than ATP Why? Is ADP more stable than ATP? Explain.

31 LE 8-8 Phosphate groups Ribose Adenine   

32 Energy from ATP hydrolysis –drives endergonic reactions Overall, coupled reactions are exergonic

33 LE 8-10 Endergonic reaction:  G is positive, reaction is not spontaneous Exergonic reaction:  G is negative, reaction is spontaneous  G = +3.4 kcal/mol  G = –7.3 kcal/mol  G = –3.9 kcal/mol NH 2 NH 3 Glu Glutamic acid Coupled reactions: Overall  G is negative; together, reactions are spontaneous AmmoniaGlutamine ATP H2OH2O ADP P i + + +

34 How ATP Performs Work Inorganic phosphate from ATP hydrolysis –Transferred to target molecule Called phosphorylation Creates highly reactive, unstable target molecule More prone to do “work” or change (conformation) –Mechanical, transport, enzymatic

35 LE 8-11 NH 2 Glu P i P i P i P i NH 3 P P P ATP ADP Motor protein Mechanical work: ATP phosphorylates motor proteins Protein moved Membrane protein Solute Transport work: ATP phosphorylates transport proteins Solute transported Chemical work: ATP phosphorylates key reactants Reactants: Glutamic acid and ammonia Product (glutamine) made + + +

36 Regeneration of ATP ADP + P i --> ATP –Energy for ADP phosphorylation from catabolic reactions

37 LE 8-12 P i ADP Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy- yielding processes) ATP +

38 Environmental Conditions Affect Enzyme Function ? Temperature: cold-->decreased chance of bumping into substrate hot--> good chance of substrate interaction but chance of denaturation at some point pH->change in charge (H+ or OH-) can denature proteins and substrate Examples of pH sensitive enzymes?

39 LE 8-18 Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic (heat-tolerant bacteria) Temperature (°C) Optimal temperature for two enzymes 020 40 6080100 Rate of reaction Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) pH Optimal pH for two enzymes 0 Rate of reaction 1 23 45 67 8 910 What is your normal body temp.?

40 Cofactors Non-protein enzyme helpers (like metals (Fe)) Coenzymes organic cofactors Vitamins e.g. Vitamin K: required for blood clotting & Required in certain carboxylation reactions

41 Regulation of Enzymes Enzyme Inhibitors Competitive inhibitor –binds to active site of enzyme –blocks substrate binding by competition Noncompetitive inhibitor – binds to another part of enzyme – causes enzyme to change shape – prevents active site from binding substrate –Allosteric effect DRAW

42 LE 8-19 Substrate Active site Enzyme Competitive inhibitor Normal binding Competitive inhibition Noncompetitive inhibitor Noncompetitive inhibition A substrate can bind normally to the active site of an enzyme. A competitive inhibitor mimics the substrate, competing for the active site. 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.

43 Allosteric Regulation of Enzymes Where protein function at one site is affected by binding of a regulatory molecule at another site May inhibit or stimulate enzyme activity

44 Allosteric Activation and Inhibition Most allosterically regulated enzymes are made from polypeptide subunits active and inactive forms binding of activator stabilizes active form of enzyme binding of inhibitor stabilizes inactive form of enzyme

45 LE 8-20a Allosteric enzyme with four subunits Regulatory site (one of four) Active form Activator Stabilized active form Active site (one of four) Allosteric activator stabilizes active form. Non- functional active site Inactive form Inhibitor Stabilized inactive form Allosteric inhibitor stabilizes inactive form. Oscillation Allosteric activators and inhibitors

46 Cooperativity –form of allosteric regulation that can amplify enzyme activity binding of substrate to one active site stabilizes favorable conformational changes at all other subunits

47 LE 8-20b Substrate Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation. Cooperativity another type of allosteric activation Stabilized active form Inactive form

48 Feedback Inhibition End product of a metabolic pathway shuts down the pathway Prevents over-production of unneeded molecules

49 LE 8-21 Active site available Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Enzyme 2 Intermediate A Isoleucine used up by cell Feedback inhibition Active site of enzyme 1 can’t bind theonine pathway off Isoleucine binds to allosteric site Enzyme 3 Intermediate B Enzyme 4 Intermediate C Enzyme 5 Intermediate D End product (isoleucine)

50 Metabolic regulation influenced by cellular localization Cellular structures organize and concentrate enzymes in pathways –Membranes, organelles (mitochondria, chloroplast)

51 LE 8-22 Mitochondria, sites of cellular respiration 1 µm

52 LE 8-22 It’s nice to get so much attention!

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