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Ppt 5   transport and enzymes-2010
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Ppt 5 transport and enzymes-2010






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  • Q: What is an enzyme? A: Biological catalyst; speeds up reactions without being consumed (true for organic and inorganic catalysts) Let’s review the potential energy diagram: 1) Relative energy of reactants and products determine endothermic / exothermic 2) Difference between reactants and transition state = activation energy Q: How does an enzyme change the shape of a potential energy diagram? (refer back to the animation) A: Lowers E A so that more reactions can happen.
  • Enzymes lower E A . Energy stored in the reactants and products don’t change. Therefore, free energy of a reaction does not change. (delta G)
  • Enzymes which act on glucose will not act on galactose.
  • Q: What part of AAs interact with substrate? A: R-groups  also involved in the t - negative acid group is attracted to the positively charged part of substrate.
  • Enzymes are not static.
  • - enzymes increase reaction rate, but only according to how many enzymes are available - enzymes are also limited by temperature and pH - think about bacteria which prefer certain environments (psychrophile vs. thermophiles) Q: What happens in “extreme” conditions? A: Denaturation (remember why we have buffers!!!) - but some enzymes prefer extreme conditions... think pH 2 stomach
  • Enzymes don’t always act alone.
  • Competitive: estrogen / tamoxifen / BPA example
  • Note the two enzyme forms. - identify various allosteric sites - note the different shapes between subunits

Ppt 5   transport and enzymes-2010 Ppt 5 transport and enzymes-2010 Presentation Transcript

  • Fluid Mosaic Model
  • Fluid Mosaic Model
    • the current understanding of all membrane structures is the fluid mosaic model
    • bilayers of amphipathic phosphlipids separate bodies of water (inside / outside cell; inside / outside organelles)
    • some integral proteins span the membrane to help with transport of some molecules across the membrane
  • Types of Transport
    • passive transport – requires no energy; [high]  [low]
      • diffusion
      • osmosis
      • facilitated diffusion
    • active transport – requires energy; [low]  [high]
  • 1. Passive Transport - Diffusion
    • molecules naturally spread from areas of [high] areas of [low]
    • membranes may or may not be involved
  • 1. Passive Transport - Osmosis
    • diffusion of water from areas of [high] to areas of [low] across a selectively permeable membrane
  • 1. Passive Transport - Osmosis
    • Why are membranes selectively-permeable?
      • outside of membrane = polar; inside membrane = non-polar
      • large molecules cannot squeeze between phospholipids
        • gases (O 2 , N 2 , CO 2 ) and small molecules (H 2 O) may pass
        • glucose, too large
      • larger molecules need the presence of its corresponding transport proteins
  • 1. Passive Transport – Facilitated Diffusion
    • molecules across a membrane from an area of [high] to and area of [low] facilitated by a transport protein
    • transport protein may:
      • be a channel or pore
      • need to change its shape to help move the molecules
  • 1. Passive Transport – Facilitated Diffusion
  • 2. Active Transport
    • molecules move across a membrane from an area of [low] to an area of [high] facilitated by a protein and the consumption of energy
    • What is the source of this energy?
      • ATP
  • 2. Active Transport
  • Membrane Transport http://www.youtube.com/watch?v=ULR79TiUj80&feature=related http://www.youtube.com/watch?v=1ZFqOvxXg9M&feature=related
  • Naming Enzymes
    • most enzymes have an –ase ending
    • the root of the enzyme name typically indicates what the substrate which it acts upon
    • ATPase
    • amylase
  • Enzymes
    • biological catalyst
    • speeds up chemical reactions without being consumed
    activation energy  E A
  • Activation Energy
    • enzymes lower E A of reactions
    • enzymes DO NOT change  G of reaction
  • Enzyme Reactions
    • enzymes can only speed up reactions which would normally occur anyway
    • substrate – reactant that binds to enzyme
    • enzymes bind very specific substrates, often an isomer will not bind
  • Enzymes are Substrate Specific
  • Enzyme Models
    • Recall: Enzymes are proteins and proteins are macromolecules with unique 3D conformations. The specificity of an enzyme results from its shape.
    • active site – pocket in which the substrate binds
    • R-groups of amino acids interact with the substrate
  • Substrate Binding
    • induced-fit model - enzyme changes shape upon substrate binding
    enzyme-substrate complex
  • Induced Fit: The active site is an enzyme’s catalytic center.
    • Change in shape to:
    • bring R-groups closer to substrate
    • bend bonds to make them easier to break / react
    • reduce E A (makes transition state easier)
    • bring two reactants close together
    • provide a microenvironment for reactions
  • Steps to Enzyme Reactions
    • Substrate binds to available active site pocket.
    • Enzyme changes shape to envelope substrate(s)
    • Reaction occurs
    • Products lose affinity for the active site
    • Enzyme is set for another substrate
  • Limitations of Enzymes
    • only a set number of each type of enzyme in body
      • reactions have a maximum rate
    • enzymes operate at optimal temperature and pH
  • Enzyme Factors
    • some enzymes require non-protein molecules to operate
    • cofactors – inorganic molecules (e.g. iron in haemoglobin)
    • coenzymes – organic molecules (NAD + ) Nicotinamide adenine dinucleotide
  • Enzyme Inhibition
    • competitive inhibitor – binds to the same active site as the substrate
    • noncompetitive inhibitor – binds to an alternate site on the enzyme to keep it in an inactive form (no longer has affinity for substrate)
  • Enzyme Inhibitor Examples
    • Poisons – DDT are inhibitors of key enzymes in the nervous system.
    • Penicillin blocks the active site of an enzyme that many bacteria use to make their cell walls.
  • Enzyme Regulation
    • allosteric site – alternative binding site away from the active site
      • often found in enzymes with 4 ° structure
      • molecules can bind allosteric site to activate or inhibit enzyme activity
    • allosteric activator – molecules which bind to allosteric site and supports an active enzyme form
    • allosteric inhibitor – molecules which bind to allosteric site and supports an inactive enzyme form
  • Feedback Inhibition
    • a method for cells to regulate metabolic pathways
    • often, products at the end of a series of a reaction will act as an allosteric inhibitor to shut the reactions down
    A, B, C and D are molecules along a metabolic pathway. E 1 , E 2 and E 3 are enzymes required for this metabolic pathway. D is an allosteric inhibitor of E 1 .
  • Cooperativity
    • binding of one substrate causes the binding of additional substrates to occur more easily.
  • Cheese
  • Rennet
    • Coagulates milk to cheese