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Eukaryotic cellular biology 1 > Secretory Pathway > Flashcards

Secretory Pathway Flashcards

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1
Q

What can be the final destination of proteins in the secretory pathway?

A

ER, Golgi, plasma membrane, lysosome, outside of cell

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2
Q

What is the difference between regulated and constitutive secretion?

A

Constitutively secreted materials are always secreted and are secreted right away after leaving the trans-Golgi network. Regulated secretion involves vesicles that won’t be secreted unless there is a signal that triggers secretion

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3
Q

What are the 5 steps common to all proteins going to the lysosomes, plasma membrane, or outside the cell?

A
  1. Proteins get targeted to the ER with an ER signal sequence
  2. ER and cis-golgi vesicles fuse and form the new cis-golgi cisterna
  3. Missorted ER proteins and some vesicle proteins get sent back to the ER
  4. The cis-golgi cisterna undergoes maturation and moves towards the plasma membrane
  5. In each cisterna, resident Golgi proteins make modifications to proteins and then sent back to the right cisterna with retrograde transport
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4
Q

What are the 4 very general steps for how vesicles work?

A

They bud off from a donor organelle, get transported to the target organelle, “dock” to the target organelle, then fuse

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5
Q

How do vesicles bud off from a donor organelle?

A

When there is enough cargo, coat proteins polymerize and that causes the membrane to curve until the vesicle gets pinched off

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6
Q

What are the 3 types of coat proteins?

A

COPI, COPII, and clathrin

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7
Q

Why are coat proteins necessary? Why do they have to be removed?

A

They are necessary because the vesicle can’t form the circular shape without them, so it can’t bud off. The receptors on the vesicle can’t bind with the target because they’re under the coat proteins, so they have to be removed

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8
Q

What direction do COPI coated vesicles go?

A

Retrograde transport from the Golgi to the ER or from a later cisterna in the Golgi to an earlier one

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9
Q

What direction do COPII coated vesicles go?

A

Anterograde transport from the ER to the Golgi

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10
Q

What direction do clathrin coated vesicles go?

A

From the trans-Golgi network to the lysosomes, and from the plasma membrane to the lysosomes

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11
Q

How do we know that a G-protein is responsible for coat assembly and disassembly?

A

Coated vesicles accumulate when around non-hydrolyzable GTP

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12
Q

How do the G-proteins trigger the coat to be assembled or disassembled?

A

The coat is assembled when bound to GTP and disassembled when bound to GDP

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13
Q

What are the two G-proteins used for coat assembly and disassembly?

A

Sar1 and ARF

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14
Q

Which coat proteins use Sar1?

A

COPII

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15
Q

Which coat proteins use ARF?

A

COPI and clathrin

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16
Q

What key shape change occurs with Sar1 and ARF to allow for coat assembly?

A

When bound to GTP, they have a tail that becomes an anchor into the membrane and allows for the coat proteins to bind to it

17
Q

What are the 4 steps in the formation of the coat of a vesicle?

A
  1. Sar1 or ARF interacts with a GEF and the tail anchors into the membrane
  2. They become a binding site for the coat proteins
  3. The GTP gets hydrolyzed and the tail retracts out of the membrane
  4. coat dissembles
18
Q

What are the two proteins responsible for directly docking and fusing vesicles to their targets?

A

v-SNARES and t-SNARES

19
Q

What is the G-protein that is involved in keeping the vesicle close enough to the target for the SNAREs to interact?

A

Rab

20
Q

How does Rab work?

A

It can put a lipid anchor into the membrane of the vesicle when bound to GTP and interacts with effectors on the target membrane. That keeps the vesicle in place long enough for the SNAREs to interact

21
Q

What happens if a vesicle tries to dock and fuse to the wrong place?

A

Nothing. The wrong t-SNAREs are around and the v-SNAREs won’t interact with them. The vesicle moves on

22
Q

How do the SNAREs draw the vesicle close to the target membrane for fusion?

A

They coil up really tight and pull the vesicle closer as they coil up

23
Q

What two proteins are needed to separate the coiled up SNAREs?

A

NSF and SNAPs, and they need ATP

24
Q

How do motor proteins work?

A

They constantly hydrolyze ATP and change shape, which makes them “walk” along the cytoskeletal filaments

25
Q

Are microtubules charged?

A

No. The “+” and “-“ ends refer to directionality and not charge

26
Q

Which motor protein moves from the + end of the microtubule to the “-“ end?

A

Dynein

27
Q

Which motor protein moves from the “-“ end of the microtubule to the + end?

A

Kinesin

28
Q

What happens when a motor protein reaches the end of a microtubule?

A

They can’t walk back in the other direction, so they hitch a ride on the cargo being carried by the other type of motor protein

29
Q

What is the microtubule organizing centre (MTOC)?

A

A location where microtubules start and extend out from

30
Q

Where is the MTOC located?

A

Right after the trans-Golgi network

31
Q

Which ends of the microtubules are anchored to the MTOC and which end extends out?

A

The minus end is attached to the MTOC and the plus end extends out

32
Q

For vesicles going from the ER to the Golgi and cis-golgi to trans-golgi:

a) what is the coat protein used
b) the G-protein that triggers coat formation
c) the motor protein
d) which direction (anterograde or retrograde)

A

a) COPII
b) Sar1
c) dynein
d) anterograde

33
Q

For vesicles going from the Golgi to the ER and trans-golgi to cis-golgi:

a) what is the coat protein used
b) the G-protein that triggers coat formation
c) the motor protein
d) which direction (anterograde or retrograde)

A

a) COPI
b) ARF
c) kinesin
d) retrograde

34
Q

Why does retrograde transport occur?

A

To bring back ER resident proteins that ended up in a vesicle by accident, recycle the membrane to keep the size constant, retrieve v-SNAREs, bring Golgi resident proteins back to the cisterna where they function

35
Q

How do ER proteins know if they are supposed to go to the Golgi?

A

They have a signal sequence, a DXE (aspartate, anything, glutamate)

36
Q

How do missorted ER proteins get sent back to the ER?

A

They have a retrieval sequence: KDEL (lysine, aspartate, glutamate, leucine) for soluble proteins and a KKXX for membrane proteins. The KDEL sequence binds to the KDEL receptor and a COPI coated vesicle forms around it and it gets brought back to the ER

37
Q

How is the KDEL receptor able to release the cargo ER protein that was brought back to the ER?

A

Affinity is lower when the pH is higher, and the pH is the highest in the ER and gets lower the further along the secretory pathway. The small change in pH makes the KDEL receptor release the KDEL

38
Q

What sort of proteins reside in the Golgi? What do they do?

A

Glycosyltransferases and glycosidases. They make modifications to the cargo proteins, most notably the sugar branches

39
Q

Why do Golgi resident proteins constantly have to be transported back with retrograde transport?

A

They are only active in a certain cisterna. So when the Golgi moves, they become inactive because of the pH change, so they have to be sent back to the right cisterna where they can do their jobs

Eukaryotic cellular biology 1 (14 decks)

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