Bio Exam II. 4

  1. Briefly summarize the LDL receptor-mediated endocytosis process?
    • LDL binds to receptors proteins
    • by endocytosis, the membrane pinches in, into a vesicle coated with clathrin
    • The clathrin-coated vesicle uncoats so that the now uncoated vesicle can fuse with another vesicle, usually an endosome.
    • The endosome will fuse with primary lysosomes, whose hydrolytic enzymes are present
    • The receptors are recycled back to the membrane and the cholesterol becomes free in th eblood
  2. Explain the transferrin cycle.
    • Ferrotransferrin (transferrin bearing an iron molecule) binds to a transferrin receptor. 
    • A coated vesicle (with clathrin) forms. The vesicle then becomes uncoated.
    • After uncoating, the vesicle fuses with an endosome. 
    • The acidity of the endosomal environment causes the iron to be released from the transferrin, which is now called apotransferrin. Iron is released into the bloodstream. 
    • Apotransferrin is recycled to the cell surface, where it dissociates from the receptor due ot the neutral pH.
  3. The transferrin process is __ dependent.
  4. Transferrin cycle:
    After endocytosis, __ is released from the __ in the __. The iron dissociates and remains in the cell. The __ remains bound to its receptor at this __, and they cycle to the cell surface together. When the __ encounters the __ of the exterior medium, the __ is released to gather its next load of iron.
    • iron
    • transferrin-receptor coplex
    • acidic late endosome/ CURL compartment
    • transferrin protein
    • pH
    • receptor-transferrin complex
    • neutral pH
    • iron-free transferrin
  5. Pathway One: Extremely brief. Explain LDL
    • coated pit
    • coated vesicle
    • uncoated vesicle
    • early endosome
    • carrier vesicle
    • late endosome
    • fuse with primary lysosomes
    • ligand degraded

    receptor recycled
  6. Pathway Two: Extremely brief. Explain transferrin.
    • coated pit
    • coated vesicle
    • uncoated vesicle
    • early endosome
    • carrier vesicle
    • late endosome
    • carrier vesicle
    • receptor and ligand recycled
  7. Pathway Three: Extremely brief. Explain EGF.
    • coated pit
    • coated vesicle
    • uncoated vesicle
    • early endosome
    • carrier vesicle
    • late endosome
    • carrier vesicle
    • receptor and ligand degraded
  8. Pathway Four: Transcytosis
    • coated pit
    • coated vesicle
    • uncoated vesicle
    • early endosome
    • carrier vesicle
    • late endosome
    • carrier vesicle
    • transcytosis
  9. What is transcytosis and what is an example?
    • the process of moving something from side of the cell to the other
    • (example: how antibodies get moved from the mom's bloodstream to the fetus)
  10. What is the major mechanical force that causes the pit to form?
    forming the lattice (polymeration)
  11. Why does (or how does) clathrin bind to the membrane?
    other proteins are involved because clathrin won't bind to the membrane itsel
  12. What is the structure of clathrin?
  13. Explain the triskelion structure.
    How do they fit together.
    • each arm is made of a heavy and a light chain (basic structure)
    • the way they fit together with another clathrin molecule is a way that forms a lattice (hexagonal kind of shape)
  14. Pathway 5
    • material can be stored in cell and taken in by receptor mediated endocytosis
    • fate: long-term storage
    • eventually, the material will be broken down
  15. __ bind on the inner side of the membrane.
    How many lipids involved? Which one?
    What does it do?
    • cytosolic proteins
    • one
    • PIP2 membrane lipid that has been phosphorylated
    • - binds proteins, assembly particles, etc. to the membrane
    • on one side, it'll bind to the membrane. On the other side, it'll bind clathrin
  16. AP-180-2
    • only in brain cells
    • may fiunction as an assembly particle
  17. One of the things that these assemblies bind to are __. They can...
    • receptors
    • help detect which receptors will be involved in pits
  18. True or False:
    there are not many assembly molecules
    • False
    • alot
  19. Adaptor complex
    each made of a complex of proteins called adaptor proteins and usually about four different kinds
  20. Assembly particles
    • found bound to both clathrin (on one side) and the membrane (on the other)
    • there is a space between the clathrin lattice and the membrane (20 nm)
  21. What do these proteins do?
    promote clathrin to form into the lattice and promote it
  22. Receptors that bind to the assembly particles have what?
    very specific ctosolic domains
  23. If there is no signal for a receptor to bind, it will be __. What varies is the __ that determines involvement in pits.
    • excluded from the pit
    • domain
  24. __ is the main mechanical force that caues the pt to form. It is facilitated by __.
    • assembly of clathrin
    • membrane proteins
  25. Explain dynamin.
    • binds to PIP2 in the membrane 
    • goes all the way around
    • molecules of dynamin are polymerizing around the neck
    • Uses GTP to sever the membrane
    • GTP is hydrolyzed and the energy is used
    • it is a cytosolic protein (components found in cytosol); 900 amino acids; absolutely essential
  26. What causes detachment of the vesicle from the membrane?
    dynamin by severing the vesicle from membrane
  27. Briefly describe a clathrin coated pit formation.
    • clathrine lattice formation and budding is regulated by AP-2, AP180, and epsin
    • Vesicle scission regulated by dynamin
    • Cuncoating induced by PIP2 dephosphylation
  28. The lipid __ is a principal player in the assembly of the molecular machinery that governs __. The __ of __, __ and __ to the plasma membrane results in __ and the __. __, recruited to the neck of the forming vesicle by binding to __, causes scission of the vesicle from the plasma membrane. The __ of vesicles are disassembled when __ dephosphorylates __, converting it to __.
    • PIP2
    • endocytosis
    • PIP-regulated recruitment
    • AP2
    • AP180
    • epsin
    • clathrin lattice formation 
    • budding of clathrin-coated vesicles
    • Dynamin
    • PiP2
    • clathrin coats
    • synaptojanin
    • PIP2
    • PIP
  29. What are the three theories of the detachment of the vesicle from the membrane?
    • When GTP hydrolyzes to GDP, it causes dynamin to change shape and sever the vesicle
    • When GTP is hydrolyzed, dynamin changes shape, causing activation of effector protein to sever vesicle
    • When GTP is hydrolyzed, it causes dynamin to contract, severing the vesicle (no disassembly)
  30. What is absolutely necessary for detachment of vesicle from teh membrane?
    GTP hydrolysis
  31. The __ of certain membrane proteins bind specificially to assembly particles that, in turn, bind to __ as it __ spontaneously over a region of membrane. Protens that do not bind to assembly particles are __ from these vesicles. __ then polymerizes over the neck of the pit; regulated by __, the neck pinches off, forming a __. __ initiates the process of vesicle budding.
    • cytosolic domains
    • clathrin
    • polymerizes
    • excluded
    • dynamin
    • dynaim-catalyzed hydrolysis of GTP
    • clathrin-coated vesicle
    • Binding of ARF-GTP to the membrane
Card Set
Bio Exam II. 4