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Cell Bio > L8. Intracellular compartments & transport II > Flashcards

L8. Intracellular compartments & transport II Flashcards

1
Q

explain how proteins are glycosylated in the ER

A
  • they are glycosylated on asparagines and serines
  • they are glycosylated by the addition of a sugar group
  • the part of the protein that is getting the sugar faces ER lumen
  • the part the has the sugar will end up outside when it gets to the plasma membrane
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2
Q

what happens to misfolded or unfolded proteins in the ER

A
  • they bind to chaperon proteins in the ER and are retained there
  • if they fail to refold properly, they are transported back to the cytosol and are degraded
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3
Q

what happens when there is an accumulation of misfolded proteins

A
  • the proteins are recognized by transmembrane sensor proteins in the ER membrane
  • each activates part of the Unfolded Protein Response (UPR)
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4
Q

accumulation of misfolded proteins - what is the Unfolded Protein Response (UPR)

A
  • can be direct or indirect
  • some of the transmembrane sensor proteins will stimulate transcriptional regulators of chaperon-encoding genes
  • others may inhibit protein synthesis, reducing the flow of protein through the ER
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5
Q

what are the types of coated vesicles

A
  • clathrin-coated
  • COP-coated: COPI and COPII
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6
Q

coated vesicles: clathrin-coated - what are the coat proteins

A
  • clathrin + adaptin 1
  • clathrin + adaptin 2
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7
Q

coated vesicles: clathrin + adaptin 1 - what is the origin and the destination

A
  • origin: Golgi
  • destination: lysosome (via endosomes)
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8
Q

coated vesicles: clathrin + adaptin 2 - what is the origin and the destination

A
  • origin: plasma membrane
  • destination: endosomes
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9
Q

coated vesicles: COP-coated - explain COPI

A
  • retrograde transport
  • goes backward
  • from Golgi to ER
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10
Q

coated vesicles: COP-coated - explain COPII

A
  • anterograde transport
  • goes forward
  • from plasma membrane to endosomes
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11
Q

transport with clathrin-coated vesicles - how is the budding initiated

A
  • cargo receptors with their bound cargo are captured by adaptins
  • they then bind to clatherin molecules to the cytolytic side and budding initiates
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12
Q

transport with clathrin-coated vesicles - what happens after budding starts

A
  • dynmin proteins assemble around the neck of the budding vesicle
  • they are GTPAses and they hydrolyze their bound GTP
  • with the help of other proteins, it pinches off the vesicle
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13
Q

transport with clathrin-coated vesicles - what happens after budding finishes

A

coat proteins are removed and the naked vesicle can fuse with its target membrane

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14
Q

transport with clathrin-coated vesicles - what happens as the vesicle fuses with the target membrane

A
  1. tethering
  2. docking
  3. fusion
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15
Q

transport with clathrin-coated vesicles - tethering

A
  • a tethering protein on the target membrane must bind to a Rab protein (monomeric GTPAse) that is on the surface of the vesicle
  • provides the initial recognition between the vesicle and the target membrane
  • this allows docking to happen
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16
Q

transport with clathrin-coated vesicles - docking

A
  • v-SNARE on the vesicle binds with the t-SNARE on the target membrane
  • this ensures that the vesicles dock at their appropriate target membrane
17
Q

transport with clathrin-coated vesicles - fusion

A
  • Release of calcium from volted gated calcium channels activates SNARE fusing with membrane
  • the complimentary SNARE proteins catalyze the final fusion of the two membranes
18
Q

transport with clathrin-coated vesicles - how do SNAREs catalyze fusion of membranes

A
  • the pairing of the SNAREs force water molecules out
  • this allows lipids to flow together to form a continuous bilayer
19
Q

transport with clathrin-coated vesicles - what happens to the SNAREs after fusion

A

SNAREs are pried apart so they can be used again

20
Q

explain the structure of the Golgi

A
  • cis Golgi network = faces ER
  • trans Golgi network = faces PM
21
Q

explain the exocytosis pathways in secretory cells

A
  • many proteins are constitutively secreted
  • specialized secretory cells undergo regulated exocytosis and the pathways diverge in the trans Golgi
22
Q

exocytosis pathways in secretory cells - what are the two pathways

A
  1. constitutive secretion = unregulated and does not require a signal for the vesicle to release contents
  2. regulated secretion = regulated and requires a signal for the vesicle to release contents
    - mechanisms unclear
23
Q

explain receptor-mediated endocytosis

A
  • ligand binds to receptors on the surface of the cell and it will be internalized in clathrin-coated vesicles
  • vesicles will then lose their coat and fuse with endosomes
  • bc of the acidic environment, the ligand dissociates from the receptors
  • ligand will then go to the lysosome and is degraded
24
Q

receptor-mediated endocytosis - what are the fates of the receptors

A
  1. recycling
  2. degradation
  3. transcytosis
25
Q

receptor-mediated endocytosis: what are the fates of the receptors - recycling

A

retrieved receptors are return to the same membrane they came from

26
Q

receptor-mediated endocytosis: what are the fates of the receptors - degredation

A

receptors that are not received go to the lysosome and are degraded

27
Q

receptor-mediated endocytosis: what are the fates of the receptors - transcytosis

A

retrieved receptors that go to a different domain of the plasma membrane

28
Q

receptor-mediated endocytosis - how do lysosomes degrade ligands

A
  • the lysosome contains hydrolytic enzymes that are only active under acidic conditions
  • the acidity is maintained by a proton ATPase
29
Q

receptor-mediated endocytosis - proton ATPase

A
  • it hydrolyses ATP to move proton from PM into endosomes
  • causes a reduction in pH and increases acidity
  • this then causes the degrative enzymes to be turned on
30
Q

what is phagocytosis

A
  • it is a form of feeding in protozoa
  • phagocytic cells can take up large molecules
31
Q

phagocytosis - how can phagocytic cells take up molecules

A
  • Affirmation of pseudopod will wrap its membrane around target and engulf it
  • Will then fuse with lysosomes and breakdown contents
32
Q

what is autophagy

A
  • the cell eats itself
  • process begins with an enclosure of the organelle by a double membrane creating an autophagosome
  • then it fuses with a lysosome
33
Q

explain the cell’s route to degradation

A

early endosomes, phagosomes, and autophagosomes can fuse with lysosomes or late endosomes for degradation

Cell Bio (21 decks)

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