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Chapter 8 Metabolism Powerpoint Templates Page 1 Flow of Energy Through Life • Life is built on chemical reactions – Transforming energy from one form to another sun Solar Energy Organic Compounds + ATP Organic Compounds Organic Compounds+ ATP Powerpoint Templates Organic Compounds Organic Compounds + ATP Page 2 Metabolism = all chemical reactions in an organism • Catabolic – – – – – Breaking Bonds Digestion Hydrolysis Polymer Monomer Releases Energy • Anabolic – – – – Forming Bonds Dehydration Monomer Polymer Requires EnergyPowerpoint Templates Page 3 Thermodynamics • The study of energy transformation – Energy = the capacity to do work • 1st Law of Thermodynamics – Energy is neither created nor destroyed but transformed (Conservation of Energy) • 2nd Law of Thermodynamics – Energy transformation increases entropy (disorder, randomness) • Combine the 2 Quantity of Energy is constant, Quality is not. Powerpoint Templates Page 4 Entropy • Disorder, Randomness Powerpoint Templates Page 5 • Living things want LESS entropy – – – – They want to be in ORDER They require ENERGY This is NOT spontaneous However, INCREASES the entropy of the universe Heat co2 + H2O (b) Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism. Powerpoint Templates Figure 8.3 Page 6 Free Energy • • • • The energy available to do work ∆G Exergonic Rxns = release free energy, decrease ∆G Endergonic Rxns = require free energy, increase ∆G Powerpoint Templates Page 7 Exergonic • Reactants have more energy than products • More ordered to less ordered (increase in entropy) • Unstable to stable (less likely to transform energy) • • • • • • Downhill rxn Free energy released ∆G negative Spontaneous Catabolic Ex: Digestion Powerpoint Templates Page 8 Endergonic • Reactants have less energy than products • Less ordered to more ordered (decrease in entropy) • Stable to unstable (more likely to transform energy) • • • • • • Uphill rxn Free energy required ∆G positive Non-Spontaneous Anabolic Ex: Polymer synthesis Powerpoint Templates Page 9 Equilibrium • Eventually a closed system (separated from outside) reaches equilibrium • ∆G = 0 ∆G < 0 Figure 8.7 A ∆G = 0 (a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium. • Living cells are open systems (materials constantly moving in and out) – prevented from reaching equilibrium Powerpoint Templates Page 10 Where do we get the energy from? • Work of life is done by energy coupling – use exergonic (catabolic) reactions to fuel endergonic (anabolic) reactions digestion + + energy synthesis + + energy Powerpoint Templates Page 11 ATP • Adenosine Triphosphate • Cellular energy • Modified nucleotide Adenine N O O -O O- O- O N CH2 O C N CH C N OH Phosphate groups Figure 8.8 C HC O O O NH2 H H H OH Powerpoint Templates Ribose OH Page 12 • Energy is released when terminal phosphate bond is broken • Becomes ADP (diphosphate) and an inorganic phosphate (Pi) • Many endergonic P P P rxns are fueled by Adenosine triphosphate (ATP) phosphorylation from HO ATP. 2 P i + Figure 8.9 Inorganic phosphate P P Energy Adenosine diphosphate (ADP) Powerpoint Templates Page 13 ATP – ADP Cycle • Can’t store ATP – Too reactive – Transfers Pi easily – Short term energy Powerpoint Templates Page 14 Activation energy • Breaking down large molecules requires an initial input of energy – activation energy – large biomolecules are stable – must absorb energy to break bonds cellulose Powerpoint TemplatesCO2 + H2O + heat energy Page 15 Reducing Activation energy • Catalysts – reducing the amount of energy to start a reaction = activation energy uncatalyzed reaction catalyzed reaction NEW activation energy reactant product Powerpoint Templates Page 16 Enzymes Decrease Activation Energy Powerpoint Templates Page 17 • Biological catalysts – Proteins Enzymes • Can be denatured – Facilitate chemical reactions • increase rate of reaction (catalyst) • reduce activation energy • doesn’t change free energy (G) released or required – required for most biological reactions – reusable – highly specific • thousands of different enzymes in cells – End in “ase” • Sucrase, Lactase, Lipase, Polymerase Powerpoint Templates Page 18 Enzymes vocabulary substrate • reactant which binds to enzyme • enzyme-substrate complex: temporary association product • end result of reaction active site • enzyme’s catalytic site; substrate fits into active site active site substrate enzyme Powerpoint Templates products Page 19 Enzyme Catalyzed Reactions Course of reaction without enzyme EA without enzyme Free energy EA with enzyme is lower Reactants ∆G is unaffected by enzyme Course of reaction with enzyme Products Progress of the reaction Figure 8.15 Powerpoint Templates Page 20 Lock and Key vs. Induced Fit • Lock and Key – Substrates fit in active site perfectly – H bonds hold substrate in active site • Induced Fit – Enzyme active site changes shape to fit snug around active site Powerpoint Templates Page 21 Factors affecting enzyme function • Enzyme concentration – as enzyme = reaction rate • more enzymes = more frequently collide with substrate – reaction rate levels off reaction rate • substrate becomes limiting factor • not all enzyme molecules can find substrate Powerpoint Templates enzyme concentration Page 22 Factors affecting enzyme function • Substrate concentration – as substrate = reaction rate • more substrate = more frequently collide with enzyme – reaction rate levels off reaction rate • all enzymes have active site engaged • enzyme is saturated • maximum rate of reaction Powerpoint Templates substrate concentration Page 23 • Factors affecting enzyme function Temperature – Optimum T° • greatest number of molecular collisions – Heat: increase beyond optimum T° • increased energy level of molecules disrupts bonds in enzyme & between enzyme & substrate • denaturation = lose 3D shape (3° structure) – Cold: decrease T° • molecules move slower • decrease collisions between enzyme & substrate Powerpoint Templates Page 24 Enzymes and temperature • Different enzymes function in different organisms in different environments reaction rate human enzyme hot spring bacteria enzyme 37°C Powerpoint Templates temperature 70°C Page 25 (158°F) Factors affecting enzyme function • pH – changes in pH • disrupts bonds, disrupts 3D shape – disrupts attractions between charged amino acids – affect 2° & 3° structure – denatures protein – optimal pH? • most human enzymes = pH 6-8 – depends on localized conditions – pepsin (stomach) = pH 2-3 – trypsin (small intestines) = pH 8 Powerpoint Templates 2611 0 1 2 3 4 5 6 7 Page 8 9 10 Factors affecting enzyme function • Salt concentration – changes in salinity • disrupts bonds, disrupts 3D shape – disrupts attractions between charged amino acids – affect 2° & 3° structure – denatures protein – enzymes intolerant of extreme salinity • Dead Sea is called dead for a reason! Powerpoint Templates Page 27 Enzyme HELPERS • Cofactors – Non-proteins, ions – Mg, K, Ca, Zn, Fe, Cu – Ex: Fe in hemoglobin • Coenzymes – Non-Protein, Organic molecules – Ex: Vitamins Powerpoint Templates Page 28 Enzyme INHIBITORS • Competitive Inhibitors – Compete for active sites – Combat by increasing substrate – Ex: Penicillin • Prevents bacterial cell enzyme from making cell walls • Bacterial cell bursts A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding A competitive inhibitor mimics the substrate, competing for the active site. Figure 8.19 Powerpoint Templates Competitive inhibitor (b) Competitive inhibition Page 29 Enzyme INHIBITORS • Non-Competitive Inhibitor – Does not bond to active site, but somewhere else – Causes enzyme to change shape – Structure-Function Relationship 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 Figure 8.19 Powerpoint Templates (c) Noncompetitive inhibition Page 30 Regulation of Enzymes • Allosteric Regulation – Enzyme’s function at one site is affected by the binding of a regulatory molecule at another site – Causes a shape change Inhibitors • keeps enzyme in inactive form Activators • keeps enzyme in active form Powerpoint Templates Page 31 Allosteric enyzme with four subunits Allosteric activater stabilizes active from Active site (one of four) Regulatory site (one of four) Activator Active form Stabilized active form Allosteric activater stabilizes active form NonInactive form functional active site Figure 8.20 Inhibitor Stabilized inactive form (a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again. Powerpoint Templates Page 32 Metabolic Pathways • Begins with a specific molecule and ends with a product • Each step is catalyzed by a specific enzyme Enzyme 1 A Reaction 1 Starting molecule Enzyme 2 Enzyme 3 D C B Reaction 2 Reaction 3 Product Powerpoint Templates Page 33 Feedback Inhibition • The end product of a metabolic pathway shuts down the pathway • AKA Negative Feedback Powerpoint Templates Page 34 Initial substrate (threonine) Example Active site available Threonine in active site Enzyme 1 (threonine deaminase) Isoleucine used up by cell Intermediate A Feedback inhibition Active site of enzyme 1 no longer binds threonine; pathway is switched off Enzyme 2 Intermediate B Enzyme 3 Intermediate C Isoleucine binds to allosteric site Enzyme 4 Intermediate D Enzyme 5 End product (isoleucine) Figure 8.21 Powerpoint Templates Page 35