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Enzymes

Alice Hathaway Biology of Cells IA Englisch 45 Karten

Enzymes

Karten in diesem Stapel (45)

  1. 1Why enzyme used?Cell reactions not spontaneous or quick enough
    Enzyme don't change equilibrium position
    Allows rapid rate at biological conditions
  2. 2RibozymesMade of RNA
    Rest of enzymes made from proteins
  3. 3Types of EnzymeTypes of Enzyme
  4. 4Prosthetic groupSmall molecule integral to structure
    Tightly bound
    Involved in catalysis
  5. 5CofactorsSmall molecules, essential for enzyme activity
    Can be tightly bound prosthetic groups, or loosely bound cosubstrates - dissociated to be regenerated
    Can be ions or organic coenzymes
  6. 6CoenzymesBased on essential vitamins needed in diets
    E.g. electron carriers as amino acid side chains have no electron carrying capacity
  7. 7How enzymes workActive site binds to substrate
    Stereospecific
    Reversibel formation of ESC
    Can breakdown or form product
    Decrease activation
  8. 8Transition stateTop of energy barrier
    Relatively unstable
    Energy change between substrate and transition state much lower in enzyme catalysis
  9. 9CatalysisSpeed up rate at which equilibrium reached
    Alternative reaction pathway
    Acid base catalysis; covalent catalysis; proximity effects; substrate strain
  10. 10Lock and keyIF true, ESC would be favourable hence product wouldn't form
  11. 11Induced FitSubtle arrangement increase complementarity, placing strain hence enzyme binds more tightly to transition state than substrate or product
  12. 12Rate depends on,,,[Enzyme]
    [Substrate]
  13. 13KmSubstrate concentration at half Vmax
    Higher - slower rate
    Michaelis Menten constant
    Intrinsc property of enzyme on substrate
    Includes how well enzyme catalysed formation of product after ESC formed
  14. 14Michaelis menten equationVmax[s]/Km[s]
  15. 15KdDissociation constant (rate constant)
    If K3 small compared to K2, Km~Kd
  16. 16K3Formation of product from ESC
    Also Kcat - turnover number
  17. 17Kcat/KmMeasure of affinity
    Large ratio = efficient enzyme
    Rate limited by diffusion of substrate
  18. 18Notable KcatCarbonic Ahydrase = 600,000/sec
    Lysozyme = 0.5/sec
  19. 19Linwever Burk EquationReciprocal of Michaelis-menten
    gradient = Km/Vmax
    Y intercept = 1/Vmax
    X intercept = 1/Km
  20. 20Units of activityKatal
    1 Katal = 1 molecule of substrate/ sec
  21. 21How do enzymes work?ESC increase local effective concentration fo reactants. Unfavourable loss of entropy when substrate binds offset by enthalpy change of binding
  22. 22Features of enzymesDenaturation destroys activity
    Stereospecific for substrate and cofactors
    Active site in hydrophobic clefts
    Enzyme interact with non-covalent interactions
    Proximity adn orientation of reactive groups of substrate important - stabilise transition state
  23. 23LysozymeNatural antibiotic in sweat, egg white, tears, saliva
    Cuts peptidoglycan at peptide links, causing lysis
  24. 24Structure of peptidoglycan linksNAG and NAM
    NAM linked with amino acid via peptide bond. D isomer hence not hydrolysed by protease
  25. 25How lysozyme worksBinds to sugar moiety
    Hydrophobic active site accommodates 6 residues, all fit easily except D - strained
    Offset by favourable bidding of others, but forced into half chair hence more reactive
    Bond between D and E cut by enzyme
  26. 26Amino acid actionGlu-35 and Asp-52 either side of bond between D and E
    Dissociate to form negatively charged carboxylate with neutral pH
    Glu-35 behave as acid (abnormal high pKA)
    Asp-52 deprotonated
  27. 27Old mechanismGlu-35 donates H to glucosidic bond, leaving ring D with positive charged carbon
    Stabilised by -ve charge of Asp-52 and lone pair O electrons.
    Carbon reacts with water activated by -ve change on Glu-35.
    Water donates OH to D and H to regenerate Glu-35
    (Incorrect - instead nucleophilic attack)
  28. 28New mechanismNucloephilic attack by Asp-52 on C1 of ring D displaces oxygen of glycosidic bond. Takes carbonyl hydrogen from glucose-35
    glycosyl enzyme intermediate reacts with water to form second product adn regenerate enzyme
  29. 29General principles of enzyme catalysisGeometric effects
    Nucleophilic attack
    acid catalysis
    electrostatic effects
    molecular recognition
    water exclusion from hydrophobic cleft
  30. 30Geometric effectsdistorted into Half chair makes more reactive and stabilised transition states
  31. 31Nucleophilic attackenzyme attack reactive group of substrate
  32. 32Acid catalysisenzyme donate H+ to first product
  33. 33Electrostatic effectsIn incorrect mechanism, carbonic ion stabilised by negative group on enzyme
  34. 34Molecular recognitionDiverse and specific recognition of several hexose residues in substrate
  35. 35Competitive inhibitorsSimilar shape, bind to AS preventing substrate
    Vmax unchanged but Km increased (slower rate)
    Overcome by higher substrate concentration
    Reversible inhibition
    e.g. methotrexate chemotherapy drug mimics folic acid, preventing DNA replication
  36. 36Irreversible Inhibitioncovalent adduct.
    much less needed to be potent
    not recycled
    targeted against amino acid side chain
    e.g. sarin in acetylcholinesterase
  37. 37Other inhibitorsChemically unreactive but use catalytic activity
    Suicide inhibitor resembles substrate
    Enzyme reacts to form covalent bond but cannot go further so commits suicide
    e.g. penicillin with serine in active site of cell wall formation in bacteria
  38. 38Reversible covalent modificationImportant and rapid.
    Mainly eukaryotes
    Initiated by extracellular signal - hormone/ growth factor
    e.g. phosphorylation of serine, threonine or tyrosine- catalysed by kinases
    Serine/ threonine control metabolism, tyrosine control cell growth and differentiation. tyrosine kinase involved in events leading to cancer
  39. 39Genetic ControlLong term control mechanism in higher eukaryotes, short term in bacteria
    Tryptophan represses production of all enzymes in tryptophan biosynthesis pathway - prevent cell wasting energy on unnecessary production
  40. 40Activation of zymogensSome enzyme produced and stored in inactive form (zymogen)
    Can be switched on when needed e.g. blood clotting and digestive enzymes
    Can only be turned off by destruction
  41. 41Allosteric EnzymesDO NOT obey Michaelis menten kinetic
    Often associated with metabolic activity
    several subunits bind to subunit
    sigmoidal shaped curve - affinity depends on if any substrate bound already (if bound, easier for next to)
  42. 42Allosteric activators/ inhibitorsActivators shift S curve left (more easily bound)
    Inhibitors shift S curve right
  43. 43Phosphofructokinase4 active sites, used in glycolysis
    controlled by allosteric effectors
    inhibited by ATP - feedback inhibition when cell doesn't need energy from glucose enzyme turned off
    AMP activates - back on when ATP low
  44. 44Cooperative bindingBehave like haem
    T state has lower oxygen affinity.
    Converted to higher R affinity by binding
    When R, easier for rest to bind
  45. 45CompartmentationKey reaction pathways catalysed by different enzymes
    Allows greater control so can activate synthesis whilst inhibiting degradation - amplifies change
    Eukaryotes can do forward and reverse in different compartment, preventing products being immediately used in opposite reaction

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Beschreibung
Biology of Cells IA (Macromolecules in the Cell) Karteikarten am Enzymes, erstellt von Alice Hathaway am 07/01/2019.
Erstellt von
Alice Hathaway
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