Cell Bio 406 Lecture 5

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smichonjohnson
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229002
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Cell Bio 406 Lecture 5
Updated:
2013-08-02 21:48:34
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Cellular Biology 406
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Channels and Gating
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  1. What makes the bilayer impermeable to polar, hydrophillic, and large molecules?
    The interior hydrophobic layer
  2. How are membrane transport proteins separated?
    channels and carriers, depending on the mode of transportation.
  3. What do ion channels do?
    catalyze the rapid and selective transport of ions down their electrochemical gradient
  4. What carries proteins?
    transporters and pumps.
  5. Why do transporters and pumps require energy?
    They transport against the electrochemical gradient.
  6. Which is faster? channels or carriers?
    channels
  7. what mediates permeation of a channel protein?
    gating mechanisms
  8. Where do channels allow permeation?
    channel pore
  9. Which membrane transport protein uses passive transport?
    Channel proteins.
  10. What is the process by which channel proteins open and close in response to stimuli?
    Gating
  11. What are the types of gating?
    • ligand-activated
    • voltage-activated
    • stretch-activated
    • temperature-activated
  12. How are carrier proteins subdivided?
    transporters and pumps
  13. How are transporters further divided?
    • uniporters
    • symporters
    • antiporters
  14. How do transporters work?
    couple with energy stores in electrochemical membrane gradients to facilitate movement
  15. How to pumps work?
    Use ATP hydrolysis to drive energetically less favorable substrate accumulation
  16. What type of transport requires energy?
    active
  17. What does primary active transport use?
    ATP
  18. How does secondary active transport work?
    electrochemical potential difference
  19. What is negative resting membrane potential?
    inside the cell is slightly more negative than outside
  20. what changes the membrane potential?
    ion movement across the membrane
  21. What is membrane potential?
    a voltage difference
  22. What is used to generate signals in electrically excitable cells?
    membrane potential
  23. how long for a movement of ions through an ion channel?
    millisecond
  24. Are large or small changes in concentration necessary for a change in membrane potential?
    very small
  25. What are action potentials?
    electrical signals that depend on several types of ion channels.
  26. What do action potentials do?
    enable rapid communication between cells.
  27. What are key elements of action potentials?
    • Na+
    • K+
    • Ca2+ currents
  28. How is membrane depolarization mediated?
    by the flow of Na+ ions into the cell through voltage dependent Na+ channels.
  29. How is repolarization controlled?
    transport of K+ ions through several different types of K+ channels.
  30. What does an alteration of action potentials signal?
    a predisposition for arrhythmias or epilepsy.
  31. What is membrane targeting of proteins?
    cells localizing proteins to specific organelles and membranes.
  32. What is the entry point into the secretory pathway?
    ER
  33. How are proteins localized to organelles?
    targeting/sorting signals (amino acid sequences in polypeptide)
  34. Where are proteins folded into correct three-dimensional structures?
    ER
  35. What are the two basic targeting pathways?
    post-translational and co-translational
  36. What is the targeting/sorting signal called?
    protein tag
  37. What happens to a polypeptide if there is no protein tag?
    It remains in the cytoplasm.
  38. How does the secretory pathway work?
    By small vesicles that bud off the membrane of the source organelle and fuse with the membrane of the distention organelle, releasing the enclosed protein within.
  39. Where do signa'/sorting sequences target nascent secretory membrane proteins to and why?
    ER for translocation
  40. What happens to secretory proteins?
    they translocate completely
  41. What happens to transmembrane proteins?
    They are integrated into the ER membrane
  42. What does the ER do?
    Fold and modify proteins
  43. How does the ER fold and modify proteins?
    enzymes and chaperones
  44. How does translocation into the cytoplasm occur?
    SRP binds to the new sequence as it emerges from the ribosome and docks it to the ER membrane
  45. What is required to translocate SRP bound ribosome/RNA into the ER?
    energy
  46. What are the steps to targeting of secretory proteins?
    • 1. Signal sequence translated at 5' end of mRNA.
    • 2. Sequence recognized by SRP and translation halted.
    • 3. SRP recognizes docking protein and brings ribosome to rough ER and signal sequence is inserted.
    • 4. SRP is released. 
    • 5. Preotein synthesis restarts and polypeptide chain is pulled through membrane. Signal sequence is cleaved off.
    • 6. Protein in lumen of RER. Ribosome is recycled.
  47. What assists in folding of newly translocated proteins?
    Chaperones
  48. What are examples of chaperones?
    Hsp-70 and Hsp-90
  49. What is BiP?
    a chaperone
  50. Where is BiP located?
    In the ER lumen
  51. How do chaperones often function?
    with cochaperones
  52. What happens to terminally misfolded proteins?
    They are targeted for degradation
  53. What degrades misfolded proteins?
    proteosome?
  54. What tells the proteosome to degrade misfolded protein?
    ubiquitin attachment
  55. what is UPR?
    • unfolded protein response activates ATF6 an d Xbp1.
    • UPR inhibits protein synthesis.
    • Triggers cell protective and cell death responses.
  56. What does rough er do?
    secretion
  57. What does smooth er do?
    steriod synthesis and drug detox
  58. What is sarcoplasmic reticulum for?
    calcium storage and release
  59. Where is sarcoplasmic reticulum?
    in contractile cells
  60. When does the composition of the ER change?
    in response to the needs of the cell
  61. How does the composition of the ER change?
    Reticulons (proteins in ER that change its curvature) form tubules
  62. What do TOM and TIM do for the mitochondrial matrix?
    associate physically and the protein being imported passes directly from one to the other.
  63. What provides energy for import into the mitochondria?
    Hsp70 (ATPase chaperone)
  64. When do proteins fold?
    before they are imported into the peroxisomes
  65. What is a peroxisome involved in?
    catabolism of fatty acids and other metabolic pathways
  66. Where are peroxisomal signal sequences recognized?
    in the cytosol
  67. Where are peroxisomal signal sequences targeted?
    To a translocation channel
  68. How many pathways are there for a peroxisomal protein?
    2
  69. What is endocytosis?
    bringing in of material from outside cell
  70. What are the three types of endocytosis?
    • phagocytosis
    • pinocytosis
    • receptor-mediated endocytosis
  71. what is exocytosis?
    discharge of material from vesicles at the cell surface to outside
  72. What is the exocytic pathway?
    ER and golgi
  73. What is the endocytic pathway?
    • early and late endosomes
    • and lysosomes
  74. What happens in vesicle-mediated transport?
    a membrane bound vesicle buds from one compartment and fuses with another
  75. Transport to plasma membrane can be ____ or ______ in the exocytic pathway.
    constitutive or regulated
  76. What is important in processing endocytosed material?
    low pH and degradative enzymes in endosomes
  77. What is the endocytic pathway for?
    used to internalize nutrients and regulate the cell surface expression of proteins
  78. What happens to endocytosed macromolecules
    they are recycles or degraded
  79. What is the pH of each endosome/lysosome
    • 6.5- early endosome
    • pH of organelle0 late endosome
    • 4.5- lysosome
  80. What is phagocytosis?
    engulfing a solid particle by a phagocyte or a protist to form an internal phagosome
  81. what is pinocytosis?
    small particles are brought into the cell forming an invagination (liquids)
  82. what is receptor mediated endocytosis?
    clathrin-mediated or caveolin-mediated
  83. What are the steps to vesicle-mediated transport?
    • 1.budding
    • 2. fission
    • 3. uncoating
    • 4. tethering
    • 5. docking
    • 6. fusion
    • (recycle)
  84. What are Rab proteins?
    small GTPases that localize to particular organelles.
  85. GDP-bound is
    cytosolic
  86. GTP-bound is
    membrane associated
  87. What happens to receptors?
    some are recycles to the cell surface. Others are degraded in lysosomes.
  88. sorting of proteins using endo/exocytic pathways leads to..
    cell polarity.

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