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Membrane Biology > Endocytosis > Flashcards

Endocytosis Flashcards

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1
Q

What is endocytosis?

A

Cells absorb molecules by engulfing them in membrane vesicles

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2
Q

What are the two fates for molecules engulfed by endosomes?

A

Plasma membrane
Lysosomes for degradation

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3
Q

What are the 3 endocytic pathways?

A

Receptor-mediated endocytosis
Phagocytosis
PInocytosis

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4
Q

Describe phagocytosis.

A

Whole particles are broken down by enzymes like cathepsins

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5
Q

Describe pinocytosis.

A

Cell engulfs material that has already been broken down
Non-specific

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6
Q

Describe phagocytosis?

A

Mechanism for the removal of pathogens and cell debris

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7
Q

How is a phagolysosome formed?

A

Particle is taken up by the phagosome
Fuses with lysosome

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8
Q

What is autophagy?

A

Cells digest their own cytoplasmic constituents within lysosomes

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9
Q

What is an autophagosome?

A

Double-membraned vesicle

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10
Q

What is cargo?

A

Transport vesicles fusing with one another and carrying membrane components and soluble molecules

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11
Q

What do cytosolic surfaces of each compartment contain?

A

Molecular markers

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12
Q

How do transport vesicles function effectively and maintain compartmental diversity?

A

Specifically take up appropriate cargo
Fuse only with correct target membranes

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13
Q

What allows the cell to segregate membranes into different sub-domains?

A

Specialized coat proteins

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14
Q

What are coat proteins 2 functions?

A

Form a specific patch
Deform membrane patch

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15
Q

What are 3 coat proteins?

A

Clathrin
COPI
COPII

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16
Q

Describe Clathrin’s structure.

A

3 large and 3 small polypeptide chains (triskelion)
Legs joined by trimerization domain
36 triskelions form a polyhedral lattice
N-terminal domains interact with inner layer of adaptor proteins

17
Q

What is the role of adaptor proteins?

A

Interact with cargo receptors that bind specific, soluble cargo molecules

18
Q

What is a retromer?

A

Heteropentameric protein complex

19
Q

What is the role of retromers?

A

Assemble on endosomes to form vesicles
Help recycling transmembrane receptors from endosome to trans-Golgi network

20
Q

When does retromer assembly only occur?

A

It can bind to tails of cargo receptors
It can interact with a curved phospholipid bilayer
It can bind to specific phosphoinositide

21
Q

How do phosphoinositides confer specificity?

A

Help determine when and where coats assemble
Used as molecular markers of compartment identity
Control trafficking

22
Q

What is Dynamin’s function?

A

Assembles around neck of clathrin coated buds
Contains phosphoinositide binding domain (tethers)
Recruits other proteins to assist in destabilizing lipid bilayers (vesicle release)

23
Q

What is the role of Rab proteins?

A

GTP-bound Rabs interact with Rab effector proteins on target membrane (guide vesicle targeting)

24
Q

What is the function of SNARE proteins?

A

Pair to dock the vesicle to target membrane
Catalyse fusion of 2 opposed bilayers

25
Q

What are the 4 steps of receptor-mediated endocytosis?

A
  1. Clathrin coated pits and vesicles uptake specific macromolecules in ECF
  2. Cargo proteins bind specific receptors in clathrin coated pits
  3. Clathrin and adaptor proteins are removed from vesicle and recycled
    Uncoated vesicle docks with its destination compartment via SNARE proteins
26
Q

What are lipid rafts?

A

Specialised cholesterol and sphingolipid-enriched microdomains

27
Q

What are the 4 types of Clathrin-independent-endocytosis (CIE)?

A

Dynamin dependent
Dynamin independent
macropinocytosis
phagocytosis

28
Q

What do invaginations of the cell membrane depend on?

A

Actin filaments

29
Q

What is the role of LDL?

A

Transport cholesterol to peripheral tissues and regulate synthesis of cholesterol at these sites

30
Q

How is LDL transported?

A

Receptor mediated endocytosis

31
Q

What are 2 regions of a LDL receptor?

A

Cytoplasmic region
Exoplasmic region

32
Q

What is hypercholesterolaemia?

A

Defective LDL receptor gene prevents binding to adaptor proteins

33
Q

What are endosomes?

A

First destination of uncoated vesicles
Heterogeneous membrane-rich set of membrane enclosed tubules/vesicles

34
Q

What are 3 classes of endosomes?

A

Early
Late
Recycling

35
Q

How do early endosomes mature into late endosomes?

A

Become more acidic by V-ATPase which breaksdown receptor/ligand complex

36
Q

Where do most ligands go after endosomes?

A

Lysosomes for degradation

Membrane Biology (19 decks)

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