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

    1. 1. Fluid Mosaic Model
    2. 2. Fluid Mosaic Model <ul><li>the current understanding of all membrane structures is the fluid mosaic model </li></ul><ul><li>bilayers of amphipathic phosphlipids separate bodies of water (inside / outside cell; inside / outside organelles) </li></ul><ul><li>some integral proteins span the membrane to help with transport of some molecules across the membrane </li></ul>
    3. 3. Types of Transport <ul><li>passive transport – requires no energy; [high]  [low] </li></ul><ul><ul><li>diffusion </li></ul></ul><ul><ul><li>osmosis </li></ul></ul><ul><ul><li>facilitated diffusion </li></ul></ul><ul><li>active transport – requires energy; [low]  [high] </li></ul>
    4. 4. 1. Passive Transport - Diffusion <ul><li>molecules naturally spread from areas of [high] areas of [low] </li></ul><ul><li>membranes may or may not be involved </li></ul>
    5. 5. 1. Passive Transport - Osmosis <ul><li>diffusion of water from areas of [high] to areas of [low] across a selectively permeable membrane </li></ul>
    6. 6. 1. Passive Transport - Osmosis <ul><li>Why are membranes selectively-permeable? </li></ul><ul><ul><li>outside of membrane = polar; inside membrane = non-polar </li></ul></ul><ul><ul><li>large molecules cannot squeeze between phospholipids </li></ul></ul><ul><ul><ul><li>gases (O 2 , N 2 , CO 2 ) and small molecules (H 2 O) may pass </li></ul></ul></ul><ul><ul><ul><li>glucose, too large </li></ul></ul></ul><ul><ul><li>larger molecules need the presence of its corresponding transport proteins </li></ul></ul>
    7. 7. 1. Passive Transport – Facilitated Diffusion <ul><li>molecules across a membrane from an area of [high] to and area of [low] facilitated by a transport protein </li></ul><ul><li>transport protein may: </li></ul><ul><ul><li>be a channel or pore </li></ul></ul><ul><ul><li>need to change its shape to help move the molecules </li></ul></ul>
    8. 8. 1. Passive Transport – Facilitated Diffusion
    9. 9. 2. Active Transport <ul><li>molecules move across a membrane from an area of [low] to an area of [high] facilitated by a protein and the consumption of energy </li></ul><ul><li>What is the source of this energy? </li></ul><ul><ul><li>ATP </li></ul></ul>
    10. 10. 2. Active Transport
    11. 11. Membrane Transport http://www.youtube.com/watch?v=ULR79TiUj80&feature=related http://www.youtube.com/watch?v=1ZFqOvxXg9M&feature=related
    12. 12. Naming Enzymes <ul><li>most enzymes have an –ase ending </li></ul><ul><li>the root of the enzyme name typically indicates what the substrate which it acts upon </li></ul><ul><li>ATPase </li></ul><ul><li>amylase </li></ul>
    13. 13. Enzymes <ul><li>biological catalyst </li></ul><ul><li>speeds up chemical reactions without being consumed </li></ul>activation energy  E A
    14. 14. Activation Energy <ul><li>enzymes lower E A of reactions </li></ul><ul><li>enzymes DO NOT change  G of reaction </li></ul>
    15. 15. Enzyme Reactions <ul><li>enzymes can only speed up reactions which would normally occur anyway </li></ul><ul><li>substrate – reactant that binds to enzyme </li></ul><ul><li>enzymes bind very specific substrates, often an isomer will not bind </li></ul>
    16. 16. Enzymes are Substrate Specific
    17. 18. Enzyme Models <ul><li>Recall: Enzymes are proteins and proteins are macromolecules with unique 3D conformations. The specificity of an enzyme results from its shape. </li></ul><ul><li>active site – pocket in which the substrate binds </li></ul><ul><li>R-groups of amino acids interact with the substrate </li></ul>
    18. 19. Substrate Binding <ul><li>induced-fit model - enzyme changes shape upon substrate binding </li></ul>enzyme-substrate complex
    19. 20. Induced Fit: The active site is an enzyme’s catalytic center. <ul><li>Change in shape to: </li></ul><ul><li>bring R-groups closer to substrate </li></ul><ul><li>bend bonds to make them easier to break / react </li></ul><ul><li>reduce E A (makes transition state easier) </li></ul><ul><li>bring two reactants close together </li></ul><ul><li>provide a microenvironment for reactions </li></ul>
    20. 21. Steps to Enzyme Reactions <ul><li>Substrate binds to available active site pocket. </li></ul><ul><li>Enzyme changes shape to envelope substrate(s) </li></ul><ul><li>Reaction occurs </li></ul><ul><li>Products lose affinity for the active site </li></ul><ul><li>Enzyme is set for another substrate </li></ul>
    21. 22. Limitations of Enzymes <ul><li>only a set number of each type of enzyme in body </li></ul><ul><ul><li>reactions have a maximum rate </li></ul></ul><ul><li>enzymes operate at optimal temperature and pH </li></ul>
    22. 23. Enzyme Factors <ul><li>some enzymes require non-protein molecules to operate </li></ul><ul><li>cofactors – inorganic molecules (e.g. iron in haemoglobin) </li></ul><ul><li>coenzymes – organic molecules (NAD + ) Nicotinamide adenine dinucleotide </li></ul>
    23. 24. Enzyme Inhibition <ul><li>competitive inhibitor – binds to the same active site as the substrate </li></ul><ul><li>noncompetitive inhibitor – binds to an alternate site on the enzyme to keep it in an inactive form (no longer has affinity for substrate) </li></ul>
    24. 25. Enzyme Inhibitor Examples <ul><li>Poisons – DDT are inhibitors of key enzymes in the nervous system. </li></ul><ul><li>Penicillin blocks the active site of an enzyme that many bacteria use to make their cell walls. </li></ul>
    25. 27. Enzyme Regulation <ul><li>allosteric site – alternative binding site away from the active site </li></ul><ul><ul><li>often found in enzymes with 4 ° structure </li></ul></ul><ul><ul><li>molecules can bind allosteric site to activate or inhibit enzyme activity </li></ul></ul><ul><li>allosteric activator – molecules which bind to allosteric site and supports an active enzyme form </li></ul><ul><li>allosteric inhibitor – molecules which bind to allosteric site and supports an inactive enzyme form </li></ul>
    26. 29. Feedback Inhibition <ul><li>a method for cells to regulate metabolic pathways </li></ul><ul><li>often, products at the end of a series of a reaction will act as an allosteric inhibitor to shut the reactions down </li></ul>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 .
    27. 31. Cooperativity <ul><li>binding of one substrate causes the binding of additional substrates to occur more easily. </li></ul>
    28. 33. Cheese
    29. 34. Rennet <ul><li>Coagulates milk to cheese </li></ul>