An organism’s metabolism transforms matter andenergy, subject to the laws of thermodynamics• Metabolism is the totality of an organism’s chemical reactions – Example of an emergent property that arises from interactions between molecules within the cell• A metabolic pathway begins with a specific molecule and ends with a product – Each step is catalyzed by a specific enzyme Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3Starting Productmolecule
A diver has more potential energy Diving converts potential energy on the platform than in the water. to kinetic energy.Climbing up converts the kinetic energy A diver has less potential energyof muscle movement to potential energy. in the water than on the platform.
Relationship of free energy to stability, work capacity and spontaneous change Unstable systems • 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 • Less free energy (lower G) • More stable • Less work capacity (c) Chemical reaction (a) Gravitational motion (b) Diffusion
Fig. 8-6 Reactants Amount of energy released Exergonic reation: Free energy (∆G < 0) energy released Energy Products Progress of the reaction Products Amount of energy Endergonic reation: required Free energy (∆G > 0) energy required Energy Reactants Progress of the reaction
Fig. 8-7 ∆G < 0 ∆G = 0An isolated hydroelectric system •Downhill flow of water turns a turbine •turbine drives a generator •Electricity turns on a light bulb •Eventually equilibrium will be reached Spontaneous reaction (b) An open hydroelectric system ∆G < 0 •Running water powers the generator •Intake and outflow of water keeps equilibrium from occurring •Electricity turns on a light bulb c) A multistep open hydroelectric ∆G < 0system ∆G < 0 •Running water powers the generator ∆G < 0 •The product becomes the reactant in the next reaction •Equilibrium will not be reached •Ex: cellular respiration Similar to a catabolic pathway that releases energy
Practice Quiz A B• Which one of these is the best example of a spontaneous reaction?• Which one is more unstable?• Which reaction is uphill? Which is downhill?• Which reaction is endergonic? Exergonic?• Which one will require more energy for work? Stable Unstable• Which one has a +∆G? Uphill Downhill Less work More work• Which one has a -∆G? Low ∆G High ∆G ∆G increases ∆G decreases• In B, is the ∆G going to decrease or increase? Nonspontaneous Spontaneous Endergonic Exergonic Absorbs energy Releases energy
NH2(a) Endergonic reaction NH3 Glu + ∆G = +3.4 kcal/mol Glu Glutamic Ammonia Glutamine acid P(b) Coupled with ATP hydrolysis, + + ADP an exergonic reaction ATP Glu Glu 1 ATP phosphorylates glutamic acid, making the amino acid less stable NH2 (exergonic). P 2 Ammonia displaces the phosphate + NH3 + Pi group, forming glutamine. Glu Glu(c) Overall free-energy change Overall exergonic reaction with energy coupling
Fig. 8-11 Membrane protein) Transport work:TP phosphorylatesansport proteins P Pi Solute Solute transported ADP ATP + Pi Cytoskeletal track (b) Mechanical work: ATP binds non- covalently to motor ATP proteins, then is hydrolyzed Motor protein Protein moved
Fig. 8-12 Energy coupling and the renewal of ATP ATP synthesis ATP hydrolysisrequires energy releases energy (endergonic) (exergonic) ATP + H2O Energy from Energy for cellular catabolism work (endergonic, (exergonic, energy-consumingenergy-releasing ADP + P i processes) processes) Exergonic reactions drive the formation of ATP (endergonic) Endergonic reactions driven by hydrolysis of ATP (exergonic)
Fig. 8-14 Energy profile of an exergonic reaction (spontaneous) AB + CD AC + BD A B Unstable transition state C D A B EA Determines the rate of the rxn Free energy C D Reactants A B ∆G < O C D Products Progress of the reaction
Fig. 8-15 The effect of an enzyme on activation energy Course of reaction EA without enzyme without EA with enzyme enzyme is lower Free energy Reactants Course of ∆G is unaffected reaction by enzyme with enzyme Products Progress of the reaction
Fig. 8-16 Induced fit between an enzyme and its substrate Substrate Active site Enzyme Enzyme-substrate complex The active site is the region on the enzyme where the substrate binds. An enzyme’s recognition of a substrate is very specific due to it AA sequence.
Fig. 8-17 1 Substrates enter active site; enzyme changes shape such that its active site 2 Substrates held in enfolds the substrates (induced fit). active site by weak interactions, such as hydrogen bonds and ionic bonds. Substrates Enzyme-substrate complex 3 Active site can lower EA and speed up a reaction. 6 Active site is available for two new substrate molecules. Enzyme 5 Products are 4 Substrates are released. converted to products. Products
Fig. 8-18 Optimal temperature for Optimal temperature for typical human enzyme enzyme of thermophilic (heat-tolerant) Rate of reaction bacteria 40 0 60 20 80 100 Temperature (ºC) (a) Optimal temperature for two enzymes Optimal pH for pepsin Optimal pH (stomach enzyme) for trypsin (intestinal Rate of reaction enzyme) 0 41 5 2 3 6 7 8 9 10 pH (b) Optimal pH for two enzymes
Fig. 8-19 Types of Enzyme Inhibition Substrate Active site Competitive inhibitor Enzyme Noncompetitive inhibitor (a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition – The shape of the enzyme is changed
Allosteric Regulation of Enzymestors and inhibitors (bind to regulatory sites) Allosteric enyzme Active site with four subunits (one of four) (b) Cooperativity Regulatory (substrate binds to active site) site (one of four) Activator Substrate Active form Stabilized active form Oscillation Inactive form Stabilized active form Non- functional Inactive form Inhibitor Stabilized inactive active form site Fig. 8-20
Initial substrate Feedback Active site (threonine) Inhibition available Threonine in active site in isoleucine Enzyme 1 (threonine synthesis Isoleucine used up by deaminase) cell Intermediate A As isoleucine Feedback accumulates, inhibition Enzyme 2 it slows down its Intermediate B own synthesis by allosterically Enzyme 3 inhibiting the enzyme for the first Active site of Intermediate C Isoleucine step of the pathway binds to enzyme 1 no Enzyme 4 allosteric longer binds site threonine; pathway is Intermediate D switched off. Enzyme 5 End product (isoleucine)Fig. 8-22
Practice Quiz1. Lists the three components of ATP.2. ________ reactions release energy while ________ reactions absorb energy3. Cells get energy from __________ to synthesize ATP from ADP and Pi. – Anabolic pathways, catabolic pathways, feedback inhibition, regeneration1. Explain how energy coupling works.2. True of False: ATP hydrolysis is exergonic and spontaneous.3. Enzymes lower the ________ of a chemical reaction.4. True or False: ∆G is decreased when an enzyme is present.5. When a protein is __________ it can become more unstable. Thus the energy from its removal can drive endergonic reactions.6. List the three types of work that ATP does.
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