Metabolic Processes

of 54

Please download to get full document.

View again

All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
PDF
54 pages
0 downs
0 views
Share
Description
Metabolic Processes. Enzymes, Energy and Chemical Reactions. Cellular Energy Processing. Metabolism : the sum of all chemical reactions Anabolism : assembly, polymerization, etc. requires energy Catabolism : disassembly, depolymerization releases energy
Transcript
Metabolic ProcessesEnzymes, Energy and Chemical ReactionsCellular Energy Processing
  • Metabolism: the sum of all chemical reactions
  • Anabolism: assembly, polymerization, etc.
  • requires energy
  • Catabolism: disassembly, depolymerization
  • releases energy
  • somereactions couple anabolism with catabolism
  • catabolism drives all anabolism
  • all reactions depend on enzyme catalysts
  • Energy can be stored or used for workFigure 6.1Cellular Energy Processing
  • cellular processes change chemical structures & transport materials
  • change and movement require energy exchanges
  • energy exchanges have to follow the law(s)
  • Cellular Energy Processing
  • First Law of Thermodynamics
  • during any event, Initial Energy = FinalEnergy
  • …neither created nor destroyedFigure 6.2Cellular Energy Processing
  • First Law of Thermodynamics
  • during any event, Initial Energy = FinalEnergy
  • Second Law of Thermodynamics
  • during any event, some energy is unavailable to do work
  • …some is unusable; disorder increasesFigure 6.2Cellular Energy Processing
  • cells obtain energy from outside sources
  • …an external source is requiredFigure 6.2Total energy =Figure 6.2 Cellular Energy Processing
  • total energy = usable energy + unusable energy, or
  • enthalpy = free energy + (entropy · absolute temperature)
  • H=G +TS, so, G=H-TS (three unmeasurable variables)
  • DG=DH-TDS (change in free energy at constant temperature)
  • DG > 0; energy requiredFigure 6.3Cellular Energy Processing
  • DG=DH-TDS describes energy changes in chemical reactions
  • positiveDG describes an energy-requiring reaction; anabolism; decrease in entropy
  • negativeDG describes an energy-yielding reaction; catabolism; increase in entropy
  • DG < 0; energy releasedFigure 6.3Cellular Energy Processing
  • spontaneity (≠ rate)
  • a spontaneous reaction goes more than half way to completion without an energy input; it is exergonic; DG < 0
  • a nonspontaneous reaction goes less than half way to completion without an energy input; it is endergonic; DG > 0
  • if A=>B is exergonic, B=>A is endergonic
  • Cellular Energy Processing
  • reactions are reversible
  • A <=> B
  • add more A, increase => rate
  • add more B, increase <= rate
  • equilibrium occurs when rates are equal
  • the closer to completion equilibrium occurs, the more free energy is released
  • reversible reaction at equilibriumFigure 6.4ATP: the cell’s chief energy currencyFigure 6.5cellular respiration supplies ATP for anabolismFigure 6.6ATP hydrolysis coupled to glutamine synthesisFigure 6.7cellular energy transfer
  • Adenosine TriPhosphate (ATP) is the predominant energy currency in the cell
  • ATP hydrolysis is exergonic (DG = -7.3 kcal/mol)
  • ATP + H2O => ADP + Pi
  • ATP synthesis is endergonic
  • ATP shuttles energy from exergonic reactions to endergonic reactions
  • each ATP is recycled ~10,000 times/day
  • ~1,000,000 ATPs are used by a cell/second
  • Enzymes: Biological Catalysts
  • a catalyst: increases the reaction rate; is unchanged by the reaction
  • most biological catalysts are proteins
  • some (few) biological catalysts are ribozymes (RNA)
  • Ea determines the likelihood that a reaction will occurFigure 6.8Enzymes: Biological Catalysts
  • each chemical reaction must overcome an energy barrier - activation energy (Ea)
  • spontaneous reactions will go - eventually
  • the direction is predictable
  • neither likelihood, nor rate is predictable
  • heatmay supplyEaFigure 6.9E + S => E-S complex => E + PFigure 6.10position substratesFigure 6.12induce strainalter surface chargeEnzymes: Biological Catalysts
  • how to overcome the energy barrier?
  • increase kinetic energy of reactant molecules, or
  • decrease Ea
  • an enzyme binds a specific substrate molecule(s) at its active site
  • E + S => E-S complex => E + P
  • the active site > positions reactants, strains bonds, etc. to destabilize the reactants…
  • …lowering Ea
  • enzyme: lowers Ea, doesn’t change DGFigure 6.11Enzymes: Biological Catalysts
  • enzymes…
  • efficiency experts of the metabolic world
  • lower activation energy
  • do not alter equilibrium
  • increase the rates of forward and reverse reactions
  • Enzymes: Biological Catalysts
  • substrate concentration affects reaction rate
  • as increased [reactant] increases reaction rate
  • so increased [substrate] increases reaction rate
  • until…
  • all active sites are occupied
  • the reaction is saturated
  • enzymatic reactions may be saturatedFigure 6.16induced fit in hexokinaseFigure 6.14Enzymes: Biological Catalysts
  • enzyme structure determines enzyme function
  • the active site fits the substrate
  • “lock & key”
  • “induced fit”
  • the rest of the enzyme
  • stabilizes the active site
  • provides flexibility
  • Figure 6.15Enzymes: Biological Catalysts
  • enzyme structure determines enzyme function
  • some enzymes require non-protein groups
  • cofators: reversibly-bound ions
  • coenzymes: reversibly bound organic molecules
  • prosthetic groups: permanently bound groups
  • Table 6.1Enzymes & Metabolism
  • metabolic regulation coordinates the many potential enzymatic reactions
  • sequential reactions form pathways
  • product of 1st reaction is substrate for 2nd
  • E1 E2 E3 E4A=> B=> C=> D=> product of pathway
  • regulation of enzymes in the pathway regulates the entire pathway
  • irreversible inhibition by DIPFFigure 6.17related to Sarin gas and malathionEnzymes & Metabolism
  • metabolic regulation coordinates the many potential enzymatic reactions
  • enzyme inhibitorsprovide negative control
  • artificial inhibitors can be pesticides
  • irreversible inhibition - covalent modification of active site
  • natural metabolic regulation is often reversible
  • competitive inhibition
  • cartoon versionFigure 6.18Enzymes & Metabolism
  • metabolic regulation coordinates the many potential enzymatic reactions
  • enzyme inhibitorsprovide negative control
  • artificial inhibitors can be pesticides
  • irreversible inhibition - covalent modification of active site
  • natural metabolic regulation is often reversible
  • competitive inhibition
  • noncompetitive inhibition
  • cartoon versionFigure 6.18Enzymes & Metabolism
  • metabolic regulation coordinates the many potential enzymatic reactions
  • allosteric enzymes have catalytic and regulatory subunits
  • active and inactive enzyme conformations are in equilibrium
  • Figure 6.19Figure 6.20Enzymes & Metabolism
  • metabolic regulation coordinates the many potential enzymatic reactions
  • allosteric enzymes regulate many metabolic pathways
  • catalyze first committed step
  • respond sensitively to inhibition
  • often inhibited by pathway end product - “end-product inhibition”
  • end-product inhibition by isoleucineFigure 6.21Enzymes & Metabolism
  • metabolic regulation coordinates the many potential enzymatic reactions
  • allosteric enzymes regulate many metabolic pathways
  • catalyze first committed step
  • respond sensitively to inhibition
  • often inhibited by pathway end product - “end-product inhibition”
  • saves resources when end product is sufficient
  • secondary & tertiary structurespH optima for three enzymesFigure 6.22temperature optimumFigure 6.23Enzymes & Metabolism
  • enzyme activity relies on proper environmental conditions
  • some enzymes have isozymes suited to different environmental conditions
  • Related Search
    We Need Your Support
    Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

    Thanks to everyone for your continued support.

    No, Thanks