Exam II Pt. 3

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  1. Endocytosis
    - what is it?
    explain phagocytosis
    •                                                               i.      Endocytosis: process by which the cell internalizes cell-surface receptors and bound extracellular ligands
    •                                                             ii.      Phagocytosis: uptake of particulate matter
  2. Endocytosis can be divided into what?
    • bulk-phase
    • 1.      receptor mediated
  3. Explain bulk phase
    • 1.      bulk-phase: (aka: pinocytosis) nonspecific uptake of EC fluids
    • a.      any molecules within fluid go into cell
    • b.      bulk-phase removes portions of the plasma membrane and may function primarily in the recycling of membrane between the cell-surface and interior compartments
  4. receptor mediated endocytosis
    a.      brings about the uptake of specific extracellular macromolecules (ligands) following their binding to receptors on the external surface of the plasma membrane
  5. Receptor-mediated endocytosis and the role of coated pits

                                                                  i.      provides a means for __uptake of macromolecules that may be present at relatively low concentrations in the EC fluid
                                                                ii.      receptors can take up dif. types of __(hormones, GFs, etc)
                                                              iii.      substances that enter a cell by means of clathrin-mediated RME become bound to receptors that collect in specialized domains of the plasma membrane, called coated pits
    • selective and efficient 
    • ligands
  6. 1.      receptors are concentrated in __ at 10-2__0 times their level in the rest of the plasma membrane
    a.      __ __ into the cytoplasm and then pinch free of the plasma membrane to form __
                                                                ii.      from cytoplasmic side, the bristly coat appears as polygons
    1.      geometric construction of the coat is derived from the structure of its clathrin building blocks
    • coated pits
    • coated pits
    • coated pits invaginate
    • coated vesicles
  7.                                                               i.      Clathrin
    1.      Each clathrin molecule consists of __ and __, joined together at the center to form a __ assembly called a __.
    a.      __in such a way that each __of a polygon contains a center of one of the component __
                                                                                                                                          i.      overlap extensively
    • three heavy chains and three light chains
    • three-legged
    • triskelion
    • overlap 
    • vertex 
    • triskelions
  8.                                                               i.      The coated vesicles that form during __also contain a layer of __situated between the __ and the surface of the __ facing the __
    1.      the best adaptor operating in connection with __ is __
    • Endocytosis 
    • adaptors 
    • clathrin lattice
    • vesicle
    • cytosol
    • clathrin-mediated Endocytosis
    • AP2
  9. AP2
    contain multiple subunits having different functions
    - alpha subunit?
                                                                                                                                          i.      μ subunit of AP2 adaptors engages the cytoplasmic tails of specific plasma membrane receptors, leading to the concentration of these selected receptors and their bound cargo into the emerging coated vesicles
  10. AP2
    contain multiple subunits having different functions
    - beta subunit?
    ii. β-adaptin subunit of AP2 adaptors binds and recruits the clathrin molecules of the overlying lattice
  11.                                                               i.      coated vesicles may have upwards of __ that form a __ of interacting molecules
    1.      these proteins have roles in __, __, __, interaction with __components, __, and __
    • two dozen different accessory proteins
    • dynamic network
    • cargo recruitment
    • coat assembly
    • membrane bending and invagination
    • cytoskeletal 
    • vesicle release
    • membrane uncoating
  12. One is dynamin. Explain it.
                                                                                                                                          i.      large GTP-binding protein that is required for the release of a clathrin-coated vesicle from the membrane on which it forms
  13.                                                                                                                                       i.      dynamin self-assembles into a __ around the __of an __, just before it pinches off from the membrane
                                                                                                                                        ii.      __of the bound __by the __ molecules induces a twisting motion in the __ that severs the __ from the plasma membrane
    1.      according to this mechanism, dynamin acts as an enzyme capable of utilizing the chemical energy of __to general mechanical forces
    • helical collar
    • neck 
    • invaginated coated pit
    • hydrolysis 
    • GPT 
    • polymerized dynamin
    • dynamin helix
    • coated vesicle
    • GTP
  14. 1.      dissociation of the __from the vesicle requires the help of an additional protein __, which is recruited to the clathrin coat by a cofactor, __
    • clathrin coat 
    • ATPase Hsc70
    • auxilin
  15.                                                               i.      __also play an important role in formation of coated vesicles
    1.      __groups can be added to different positions of the sugar ring of the phospholipid __, converting them into __
    • phospholipids 
    • phosphate 
    • PI
    • phosphoinositides
  16. a.      the phosphorylated rings of these __reside at the surface of the membrane where they can be recognized and bound by particular proteins = “__”
    • phosphoinositides 
    • surface identity
  17.                                                                                                                                       i.      The inner leaflet of the plasma membrane tends to contain elevated levels of __, which plays an important role in __
    • PI(4,5)P2
    • recruiting proteins involved in clathrin-mediated Endocytosis, such as dynamin and AP2
  18. 1.      not only can a __aid in recruiting specific proteins, it can also induce __ in a bound protein that facilitate a molecular process
    Explain an example. 
    • phosphoinositide 
    • conformational changes

    a.      the clatrhin adaptor AP2, for ex., normally exists in the cytosol in a locked conformation until binding of the AP2 complex to PIP2 causes a conformational change in AP2 that opens a cargo binding site within the adaptor, allowing it to interact with the cytoplasmic tails of specific membrane receptors
  19.                                                               i.      a __species like __can have a dynamic regulatory role because it can be __that are localized at particular places and times within the cell
    1.      in Endocytosis, PIP2 disappears from a site of Endocytosis about the time the coated vesicle is pinched away from the plasma membrane
    • lipid 
    • PIP2 
    • rapidly formed and destroyed by enzymes
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Exam II Pt. 3
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