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Cell Biology > Endocytosis > Flashcards

Endocytosis Flashcards

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1
Q

what is endocytosis?

A

the inward budding of the plasma membrane to form a vesicle/endosome

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2
Q

what is pinocytosis?

A
  • ‘cell drinking’
  • plasma membrane recycling
  • transcytosis - movement of molecules from apical to basolateral
  • pulling in extracellular fluid
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3
Q

what is constitutive and receptor mediated endocytosis?

A
  • inital acute response and then internalise the response
  • signalling
  • nutritional
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4
Q

what is secretory vesicle endocytosis?

A

partially fuse to release and then rapidly endocytose

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5
Q

what phaocytosis?

A
  • ‘cell eating’

- large particles

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6
Q

what are the criteria for endocytosis?

A
  • either clathrin dependent or independent endocytosis

- type of of endocytosis can be defined by the molecules involved

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7
Q

what are the principles of endocytosis?

A
  1. deform the membrane
  2. include or exclude proteins/lipids in the budding compartment
  3. ‘budding’ of the compartment and from the plasma membrane
  4. uncoat the vesicle and deliver (fuse) the cargo to another compartment
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8
Q

why does they membrane need to be deformed?

A
  • the lipid bilayer is extremely stable

- its very flat but needs to form a bud

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9
Q

what are amphipathic helices?

A
  • polar and hydrophobic amino acids on opposite sides of the helix
  • top half of the lipid bilayer becomes deformed (get a curve)
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10
Q

what is a loop insertion?

A

loops with a hydrophobic amino acid

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11
Q

what are classic lattices?

A
  • bend the membrane, forces it into a curve

- lattices bind cargo proteins but the lattice forms a curved polymer

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12
Q

what are BAR domain proteins?

A
  • proteins bind the bilayer via a curved surface
  • e.g. BAR domain containing proteins
  • binds in 2 different places
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13
Q

what does including or excluding cargo involve?

A
  • two protein complexes/molecular hubs
  • clathrin
  • adaptor protein 2 (AP-2)
  • these protein complexes form molecula hubs binding cargo at the plasma membrane
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14
Q

what does AP2 do?

A
  • binds a huge number of proteins
  • these protein complexes from molecular hubs
  • binds cargo at the plasma membrane with the aid of accessory proteins
  • can bind the same proteins
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15
Q

what do AP2 and clathrin allow?

A

allows the membrane to deform and can the internalise the transmembrane cargo proteins

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16
Q

what are cargo adaptors?

A
  • proteins that link cargo into the clathrin-coated pits

- AP2 is the adaptor protein at the plasma membrane

17
Q

what do appendage domains bind?

A
  • they bind accessory proteins
  • appendages
  • the hing regions bind to clathrin
  • binds motifs
18
Q

what do trunk domains do?

A

bind to membranes and cargo

19
Q

what is the process of AP2?

A
  • initially in a closed confirmation
  • AP2 docks with the plasma membrane where it binds the plasma membrane lipid PI(4,5)P2
  • 4 x PI(4,5)P2 per AP2 allows cargo binding following a conformation change
  • once AP2 is bound to cargo it can then bind to clathrin
20
Q

what is the structure of the clathrin coat?

A
  • consists of triskelions: 3 heavy and 3 light chains
  • assemble to form a clathrin cage around a membrane
  • hexagons and pentagons like a football
21
Q

what are the steps of clathrin mediated endocytosis?

A
  • AP2 and clathrin help to deform the membrane
  • receptor binds to ligand, binds AP2
  • AP2 binds PI(4,5)P2 and recruits clathrin
  • form clathrin triskelions allowing the membrane to deform
  • receptor is concnetrated in the vesicle
  • the stalk is cleaved
  • uncoating of the clathrin and AP2
  • these can be recycled
22
Q

what do clathrin and AP2 bind?

A
  • bind accessory proteins

- accessory proteins are not one to one

23
Q

how is clathrin dependent endocytosis achieved?

A

through sequential protin-protein interactions at the site of vesicle budding

24
Q

what is budding?

A
  • vesicle scission

- forms a clathrin cage but still attached to the plasma membrane

25
Q

what is the process of budding?

A
  • hexameric GTPase
  • forms a ring around the neck of the budding vesicle
  • uses GTP hydrolysis to achieve fission
26
Q

how does the does the vesicle finally bud off?

A
  • constrict (narrows in width)
  • twists in opposite directions
  • distance between subunits become smaller
  • pinches the membrane
27
Q

what is shibire?

A
  • temperature mutant, vesicles get pinched off and so line up at the plasma membrane
28
Q

what happens when the receptor associates with the clathrin-coated pit?

A
  • endocytosis
  • uncoating
  • fusion with early endosome
29
Q

how does fusion with early endosome occur?

A
  • maturation to late endosome (near Golgi, more acidic thatnEE and different Rabs)
  • fusing with/trafficking to lysosome for degradation
  • recycling to plasma membrane via transport vesicles that bind from EE and can fuse to form recycling endosomes
30
Q

what are the different receptor fates?

A
  1. receptor recycles between an intracellular compartment and plasma membrane
  2. transcytosis
  3. degradation
31
Q

what does the LDL receptor bind to?

A

ApoB

- association NPXY motif with AP2+ localises it to CCP

32
Q

what is the clathrin-coated pit?

A
  • coated vesicle

- uncoating and then fusion with an endosome

33
Q

how is the LDL receptor recycled?

A
  • acidic pH in endosome, dissociates ligand from receptor
  • receptor is recycled back to plasma membrane
  • LDL is sent to lysosome for degradation
34
Q

what happens in an inherited LDL trafficking disorder?

A
  • familial hypercholesterolemia (one of 2 defects)
  • mutations of NPXY motif
  • mutation of AP2 adaptor
35
Q

what is the process of EGF receptr degradation?

A
  • only associates with CCP on ligand binding (fast endocytosis)
  • EGF, tetrapeptide internalisation sequence interacts with AP2
  • internalisation involves tyrosine kinases activity
  • most EGF receptors are degraded in the lysosome
  • leading to receptor and ligand down-regulation/degradation

Cell Biology (10 decks)

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