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Cell Bio > Membrane Trafficking > Flashcards

Membrane Trafficking Flashcards

1
Q

proteins are transported to organelles by while mechanisms

A
  • pores
  • protein translocators
  • transport vesicles
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2
Q

what are pores

A

selective gates that actively transport specific molecules and allow free diffusion of smaller molecules

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3
Q

what do protein translocators do

A

transport proteins (typically unfolded) into organelles

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4
Q

how do transport vesicles work

A

pinch off from the membrane of one compartment and then fuse with another

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5
Q

what are the two methods of vesicular transport

A
  • exocytosis
  • endocytosis
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6
Q

what is exocytosis

A
  • vesicle releases contents to extracellular space
  • a vesicle fuses w the plasma membrane, releasing its contents to the extracellular space
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7
Q

what is endocytosis

A
  • extracellular materials come into the cell via a vesicle
  • extracellular materials are captured by vesicles that bus inward from the plasma membrane and are carried into the cell
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8
Q

where do transport vesicles move stuff

A
  • in and out of the cell
  • between compartments of the cell
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9
Q

what is the endomembrane system

A

a collection of organelles that are interconnected by the movement of vesicles

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10
Q

vesicle budding is driven by what and why

A
  • the assembly of a protein coat
  • helps shape the vesicle and capture molecules for transport
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11
Q

the best studied vesicles are which

A

those that have an outer coat made of the protein clathrin

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12
Q

what do adaptins do

A

help select cargo receptors and cargo for movement

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13
Q

what do clathrins do

A

bind to the adaptins and help shape the vesicle from the cytosolic surface

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14
Q

describe the steps of vesicle formation w clathrins

A
  • adaptins select cargo receptors and cargo for movement
  • clathrins bind to the adaptins, to help shape the vesicle from the cytosolic surface
  • dynamin assembles around the neck of the budding vesicle, then hydrolyzes their bound GTP and pinches off the vesicle
  • the coat proteins (clathrin and adaptin) are removed, and the vesicle is free to fuse to its target membrane
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15
Q

what is dynamin

A

a GTP-binding protein

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16
Q

where are vesicles often transported and how

A
  • actively transported
  • along the cytoskeleton
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17
Q

how does identification/ recognition happen in vesicular docking

A
  • depends on GTPases called Rab proteins on the vesicle surface
  • Rab proteins are recognized by corresponding tethering proteins on the cytosolic organelle surface
  • SNAREs which are transmembrane proteins also help
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18
Q

describe the steps of vesicular docking

A
  • Rab proteins on the vesicle surface are recognized by corresponding tethering proteins on the cytosolic organelle surface
  • once tethered, v-SNAREs and t-SNAREs firmly dock the transport vesicle
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19
Q

what is the role of SNAREs in vesicular docking

A
  • additional recognition
  • v-SNAREs and t-SNAREs dock the vesicle
  • also catalyze the fusion of transport vesicles to their target membrane
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20
Q

describe what happens in vesicle fusion

A
  • sometimes requires a stimulatory signal
  • fusion complexes bring the membranes closer together so that their lipid bilayers can interact (ie displacing water from the hydrophilic surface)
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21
Q

what is the major secretory pathway of the endomembrane system

A

ER to golgi to plasma membrane

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22
Q

what is the major endocytic pathway of the endomembrane system

A

plasma membrane to early endosome to late endosome to lysosome

23
Q

which processes balance the amount of membrane added to or removed from the surface

A
  • major secretory pathway
  • major endocytic pathway
24
Q

what are common protein modifications that happen in the ER

A
  • chemically modified (happens en route but starts in the ER)
  • converted to glycoproteins
  • transfer of oligosaccharides to new proteins
25
Q

why does the ER transfer oligosaccharides to new proteins sometimes

A
  • glycosylation enzymes are present exclusively in the ER lumen
  • these transfer oligosaccharides to Asp residues in the newly synthesized protein
26
Q

what bonds help with protein folding and stability

A

disulfide bonds

27
Q

what helps guide protein folding and prevent misfolded or partially assembled proteins from leaving the ER

A

chaperone proteins

28
Q

what do chaperone proteins do

A

helps guide protein folding and prevent misfolded or partially assembled proteins from leaving the ER

29
Q

how do chaperones helps guide protein folding and prevent misfolded or partially assembled proteins from leaving the ER

A
  • The chaperones bind to newly synthesized or partially folded chains
  • help them to fold along the most energetically favourable pathway
  • requires ATP binding and hydrolysis.
30
Q

how do isolation chamber chaperones helps guide protein folding and prevent misfolded or partially assembled proteins from leaving the ER

A
  • provides an enclosed chamber in which a newly synthesized polypeptide chain can fold without the risk of aggregating with other polypeptides in the crowded conditions of the cytoplasm.
  • requires an input of energy from ATP hydrolysis
31
Q

what happens if too many misfolded proteins accumulate

A

the unfolded protein response (UPR) is generated

32
Q

what does the unfolded protein response (UPR) do

A
  • boosts the production of proteins involved in quality control (like chaperones)
  • allows a cell to adjust the size of its ER according to the load of proteins entering the secretory pathway
33
Q

describe the structure of the golgi

A
  • 3 20 membrane bound sacs called cisternae in the middle (cis, medial and trans)
  • surrounded by cis golgi network and trans golgi network
34
Q

describe vesicular transport through the golgi

A
  • proteins leaving the ER move to the cis face of the golgi and fuse
  • they are sorted and modified here w addition of oligosaccharides
  • they head through the stack and exit on the trans face to go in diff direction
35
Q

what are the two methods of secretion by the golgi

A
  • constitutive pathway
  • regulated pathway
36
Q

what does the constitutive pathway do

A

provides a steady stream of proteins and lipids to the plasma membrane and extracellular space

37
Q

where is the constitutive pathway active

A

in all eukaryotes

38
Q

what does the regulated pathway do

A

large quantities of signals stores in vesicles for later release

39
Q

where is the regulated pathway active

A

in cells specialized for secretion

40
Q

what happens when proteins are ready to be secreted

A
  • they aggregate and accumulate in high [ ] in vesicles
  • there contends are finally released through docking and fusion in response to a signal
41
Q

what is phagocytosis

A
  • “cell eating”
  • ingestion of large particles such as microbes via large vesicles called phagosomes
42
Q

where does phagocytosis occur

A

in specialized phagocytic cells

43
Q

what is pinocytosis

A
  • “cell drinking”
  • indiscriminate ingestion of fluid and molecules via small pinocytic vesicles
  • vesicles fuse w endosomes and lysosomes, the material inside is degraded
44
Q

where does pinocytosis occur

A

in all cells (with the aid of coat proteins)

45
Q

how is specific material taken up in the pinocytosis

A

receptor-mediated endocytosis

46
Q

describe the steps of receptor-mediated endocytosis- LDL

A
  • cholesterol binds to LDL to be transported through the bloodstream
  • LDL binds to receptors on the plasma membrane and is internalized in clathrin-coated vesicles
  • vesicles lose their coat and fuse w endosomes
  • endosomes are acidic, which dissociates the LDL from its receptor
  • LDL is delivered to a lysosome, where it is degraded, releasing the cholesterol
  • LDL receptors return to the plasma membrane to be used again
47
Q

how do viruses exploit receptor-mediated endocytosis

A
  • virus binds to receptors on cell surface
  • receptor-mediated endocytosis of virus
  • fusion of virus w cell and entry of viral genome
48
Q

how are the golgi and endosomes alike

A
  • golgi serves as a sorting station in the secretory pathway
  • endosomes do the same in the endocytic pathway
49
Q

what routes can be taken by receptors once they have released their cargo

A
  • recycling back to plasma membrane
  • degredation to lysosomes
  • transcytosis to diff domains of plasma membrane
50
Q

where does much of the material that is endocytosed end up

A

in lysosomes (where it is degraded)

51
Q

how do lysosomes break down macromolecules

A

contains a large variety of hydrolytic enzymes which function at a low pH

52
Q

where does material that has been digested in lysosomes go

A

into the cytoplasm for reuse

53
Q

how do cells digest old organelles or groups of proteins

A

via autophagy

54
Q
A

Cell Bio (11 decks)

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