Cell Bio ch 15 intracellular compartments and transport

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  1. endoplasmic reticulum (ER)
    synthesis of most lipids; synthesis of proteins for distribution to many organelles and to the plasma membrane
  2. Golgi apparatus
    modification, sorting, and packaging of proteins and lipids for either secretion or deliver to another organelle
  3. endosomes
    sorting of endocytosed material
  4. Cytosol % of total cell volume and approximate number per cell
    54% cell volume, 1 per cell
  5. Mitochondria % of total cell volume and approx. number per cell
    22% cell volume, 1700 per cell
  6. Endoplasmic reticulum % of total cell volume and approximate number per cell
    12% cell volume, 1 per cell
  7. Nucleus % of total cell volume and approximate number per cell
    6% cell volume, 1 per cell
  8. Golgi Apparatus % of total cell volume and approximate number per cell
    3% cell volume, 1 per cell
  9. 3 general types of transport
    • 1) nuclear pores such as mRNA
    • 2) across intracellular membranes into other organelles, or across plasma membrane from outer environment
    • 3) by vesicles to either the Golgi or another membrane bound organelle, or to the plasma membrane for secretion
  10. Signal sequence of import into ER
    Leucine and hydrophobic amino acids
  11. Signal sequence of retention of lumen in ER
    negatively charged amino acids and contains asp
  12. Signal sequence of import into mitochondria
    positively charged and arginine
  13. signal sequence into the nucleus
    positively charged and lysine
  14. Perinuclear space of nucleus is analogous to
    the ER lumen
  15. transport into the nucleus
    • proteins must have a nuclear signal sequence.
    • then becomes bound by a nuclear transport receptor
    • nuclear transport receptor and nuclear pore interactions pull protein into the nucleas where a GTP then binds to the receptor
    • receptor and GTP leave together while the protein stays inside
    • GTP is then hydrolyzed to GDP
  16. transport into mitochondria
    • initial contact is between signal sequence and receptor protein on outer mitochondrial membrane (also attached to a protein translocator)
    • entire complex diffuses in membrane until it reaches another contact site on inner membrane that has another protein transporter
    • chaperones pull protein in and refold it, then signal sequence is cleaved
  17. transport into ER lumen
    • Signal recognition particle (SRP) binds to the ER signal sequence on growing polypeptide
    • complex then binds to SRP receptor located in the ER membrane
    • entire protein passes through a translocation channel and SRP dissociates and recycles
    • As polypeptide chain passes through translocation as a loop at some point the signal sequence is cleaved by peptidase
  18. peptidase
    cleaves off signal sequence of polypeptide chain
  19. what anchors a transmembrane protein in the membrane
    hydrophobic stop-transfer sequence
  20. Clathrin coated pits
    • receptors bind to their ligands, then are bound by adaptins
    • adaptins then bind to clathrin and vesicle is pinched off by dynamin
    • once inside uncoating occurs to leave only the ligand~receptor complex inside the cell
  21. Clathrin+adaptin 1 origin and destination
    • origin = Golgi appartus
    • destination = lysosomes (via endosomes)
  22. Clathrin+adaptin 2 origin and destination
    • origin = plasma membrane
    • destination = endosomes
  23. COP (coat proteins) origin and destination
    • origin = ER, Golgi cisterna, and Golgi apparatus
    • destination = Golgi apparatus, Golgi cisterna, and ER
  24. Delivery of an uncoated vesicle to its destination:
    • Tethering - involves a family of proteins called Rab, that bind to outer membrane of the vesicles. Rab engages tethering proteins on the target membranes
    • Docking - mediated by SNARE proteins (v-SNARE and t-SNARE) which are embedded in the vesicle and target membranes
    • Fusion - membrane fusion and ligand delivery
  25. SNARE proteins
    serve to bring vesicle and target membranes into close contact prior to membrane fusion
  26. N-linked oligosaccharides
    • within the ER lumen, a common glycolipid, dolichol, donates its oligosaccharides to new proteins at Asn residues through a transferase
    • this modification of this common oligosaccharide chain yields protein with specific sugar motifs attached
  27. What if there is an excess of proteins in the lumen?
    • the ER only expands up to a point and if there is too much the apoptotic program is triggered
    • controlled by unfolded protein response (UPR)
    • ER doesn't allow immature or misfolded proteins to pass cytosol or to be packaged in vesicles for transport.
  28. Cis golgi
    • adjacent to the ER
    • vesicles either move through the stacks of cisterna towards the trans Golgi or are routed back to the ER
  29. trans golgi
    • oriented towards the plasma membrane
    • vesicles are destined for either lysosomes or the plasma membrane for export of contained products
  30. Constitutive secretion
    replacement of lipids/proteins for the plasma membrane, basement membrane components, etc.
  31. regulated secretion
    • specialized products
    • hormones, mucus, digestive enzymes, etc. Insulin. Secretion in response to a signal
  32. Macrophages
    professional phagocytes that engulf microbial invaders in phagocytic vacuoles, which then fuse with lysosomes
  33. lysosomes
    • acidification due to H+ ATPase which brings pH to 5.0
    • also contain other degradative enzymes that destroy endocytosed or phagoytosed organisms
  34. Phagolysosome
    • lysosomes fused with phagosomes for microbial destruction
    • these can be beaten by pathogens that inhibit phagolysosomal fusion
    • ex. Mycobacteria multiply inside the phagosome
    • Listeria break out of phagolysosome into the cytoplasm
  35. Mycobacteria
    inhibit phagolysosomal fusion by inserting waxy lipids into the phagosomal membrane
  36. Receptor mediated phagocytosis
    • low density lipoprotein (LDL) is a protein that binds cholestorl and is implicated in cardiovascular disease
    • LDL is bound by cell surface receptor in a clathrin coated vesicle. vesicle uncoats and fuses with endosome
    • receptor buds off within transport vesicle for recycling to the cell surface
    • LDL~cholesterol is transferred to a lysosome, where hydrolytic enzymes destroy LDL and free cholesterol into the cytosol
  37. Different receptor pathways from endocytic compartments
    • 1) recycling of receptors can occur from early endosomes. Late endosomes found near nucleus or fused with lysosomes
    • 2) degradation of receptors due to endosomal-lysosomal fusion
    • 3) transcytosis of endosomal contents in transport veislces that bud off early endosomes. this usually takes place in polarized cells like gut epithelial cells
  38. Pathways to lysosomal function
    • 1)phagocytosis - phagosomes fuse with lysosomes to yield phagolysosomes -> destruction of microbial invaders
    • 2) endocytosed materials from outside can be taken in as endosome, early endosome -> late endosome -> incorporation into a lysosome for destruction
    • 3) autophagy of old mitochondria which is very important since any mitochondrial leaks lead to apoptosis. tip off is finding cytochrome C which shouldn't be there
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Cell Bio ch 15 intracellular compartments and transport
cell bio intracellular compartments and transport
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