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Molecular 2018 > Lecture 17 > Flashcards

Lecture 17 Flashcards

1
Q

True or False: Vesicular transport is Bidirectional

A

True

it is technically both directional and bidirectional (retrieval pathways are what makes it bidirectional)

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2
Q

What determines where a vesicle will end up and how it gets there?

A

the composition of it’s membrane and molecular markers on the surface of that membrane AND complementary receptors on the target membrane.

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3
Q

describe the location of the coat on coated proteins

A

on the cytosolic side of the membrane

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4
Q

What are the 2 major functions of the coat on coated vesicles?

A

Concentrates selected proteins for transport

Molds the vesicle to form a basket-like lattice (gives shape to the membrane)

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5
Q

The coat is _____ when the vesicle reaches the target membrane

A

discarded

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6
Q

What is the function of COPI?

A

mediates transport from the golgi cisternae

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7
Q

What is the function of COPII?

A

Mediates transport from the ER

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8
Q

What is the function of Clathrin-coated vesicles?

A

mediates transport from the golgi and from the plasma membrane

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9
Q

Describe the structure of a clathrin subunit and give the term that describes the structure they form.

A

3 large and 3 small polypeptide chains that come together to form a “3 legged structure” called the

Triskeleton

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10
Q

where are triskeleton’s found, and describe their structure in geometric terms.

A

Found on the cytosolic side of the membrane

basket-like structure of hexagons and pentagons that form coated pits

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11
Q

in clathrin coated vesicles, what forms the second layer between the clathrin cage and the membrane-bound cargo receptors?

A

adaptor proteins

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12
Q

Assembly of a protein molecule coat induces what effect on the membrane?

A

curvature

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13
Q

what type of recuitment of membrane and cargo molecules occurs in a vesicle?

A

selective

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14
Q

what are cargo receptors bound to?

A

cargo molecules on one end and adaptor proteins(which will be attached to a clathrin subunit) on the other

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15
Q

What family of molecules plays a major role in coat assembly, vesicle formation, and protein trafficking?

A

Phosphoinositides (PI)

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16
Q

What do different organelles have in order to facilitate interconversion?

A

unique sets of PI kinases and Phosphatases

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17
Q

What is the purpose of Phosphatidylinositol?

A

interconversion occurs to change it between various phosphoinisitides to control the recruitment and binding of adaptor proteins for the specific needs of that organelle/domain.

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18
Q

Define what interconversion is

A

rapid cycles of phosphorylation and dephosphorylation at the 3’, 4’, and 5’ positions of phosphoinositides to form various derivatives.

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19
Q

What part of Phosphoinositides is recognized by proteins?

A

the head group (inositol to be exact) that serves as a “signature”

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20
Q

What are BAR domains?

A

proteins with “coiled coils” that bend membranes

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21
Q

How do BAR domains bend membranes?

A

they have a positively charged inner surface that interacts with the negatively charged lipid head groups of the membrane (bends it)

22
Q

What removes clathrin coats from vesicles? how does this process happen?

A

Dynamin removes clathrin coats by first forming a ring around a clathrin bud.

The PIP2 binding domain and GTPase domain help “pinch” the membrane together

Dynamin recruits other proteins to “distort the lipid bilayer” and the vesicle looses it’s coat.

23
Q

Once dynamin recruits other proteins to distort the lipid bilayer, how are the adaptor proteins unbound?

A

PIP2 is degraded once the vesicle looses it’s clathrin coat and that weakens the binding of adaptor proteins.

24
Q

what protein physically peels off the clathrin coat?

A

HSP 70 chaperone protein and it uses ATP to do this

25
Q

What are Rab protiens and what do they do?

A

Rab proteins are monomeric GTPases that play a central role in the specificity of vesicular transport

26
Q

Compare and contrast the inactive and active forms of Rab protein. where are these found?

A

Inactive: Rab in the GDP-bound form ; found in the cytosol (soluble form)

Active: Rab in the GTP-bound form ; found in the membrane

27
Q

What are Rab effectors and where are they found?

A

motor proteins/tethering proteins that the active form of Rab binds to

in the target membrane

28
Q

(Rab Proteins)

name the sub-cellular location of Rab1

A

ER and Golgi

29
Q

(Rab Proteins)

name the sub-cellular location of Rab3A

A

Synaptic vesicles and secretory vesicles

30
Q

(Rab Proteins)

name the sub-cellular location of Rab5

A

Early endosomes, the plasma membrane, and in clathrin-coated vesicles.

31
Q

What is the general function of snares? what are the 2 types?

A

they catalyze the fusion of vesicles with membranes

v-SNAREs and t-SNAREs

32
Q

explain the locations of vSNAREs and tSNARES and how they interact

A

v: vesicle membrane
t: target membrane

they wrap around each other to lock 2 membranes together

33
Q

what is the first step of docking and the first step of fusion?

A

docking: the rab effector binds to RabGTP
fusion: the trans-SNARE complex is formed

34
Q

define the Rab5 domain on an endosome membrane

A

a “soft spot” of phosphorylated PI’s, filamentous tethering protiens, and Rab effector proteins in the membrane where the vesicle can be more easily received into the cell

35
Q

describe how Rab5 domains are formed

A

Rab5-GEF adds a phosphate to create Rab-GTP (from Rab-GDP)

Rab5-GTP activates the PI 3-kinase which creates PI(3)P (on the membrane)

PI(3)P creation recruits more Rab5-GEF, whose repeated activity form the Rab5 domain

36
Q

describe how a trans-SNARE complex is dissociated

A

NSF (activated by an accessory protein) hydrolyzes ATP to untangle the transSNARE complex

37
Q

what are newly synthesized proteins packaged into? where do these vesicles originate?

A

COPII coated transport vesicles

they bud off the ER

38
Q

What role to exit signals have in the formation of transport vesicles from the ER?

A

they are recognized by receptors on the COPII (this is what keeps the process selective)

39
Q

What happens to incompletely folded/mislfoded proteins that enter the ER?

A

they are retained in the ER by binding to BiP or calnexin

then they are degraded

40
Q

compare and contrast homotypic and hetertypic vesicle fusion. What does this result in?

A

homo: describes vesicles from the same compartment
hetero: describesV’s from a different compartment

these form vesicular tubular structures

41
Q

what is crucial to the process of vesicle fusion? where re these found?

A

vSNAREs and tSNAREs

both vesicles contribute both of these to the process

42
Q

how to vesicular tubular clusters migrate around the cell?

A

they use motor proteins to crawl along microtubules

43
Q

retrieval transport vesicles use what type of coat, and what is their origin/destination?

A

COPI coat

moving from cis Golgi back to the ER

44
Q

What does the retrieval pathway depend on? give 2 examples of these

A

ER retrieval signals at the C terminus

KKXX (in the ER) 
KDEL sequence (in soluble proteins)
45
Q

what is the main difference between KKXX and KDEL ER retrieval signals?

A

KKXX interacts with COPI directly while soluble proteins require a KDEL receptor to be packaged into COPI vesicles

46
Q

list and describe the 2 faces of the Golgi

A

Cis: network of fused vesicular tubular clusters arriving from the ER (proteins/lipids enter here)

Trans: region that allows the exit of secretory vesicles (part of secretory pathway)

47
Q

what lies between the cis and trans faces of the golgi?

A

the medial cisterna of the golgi

48
Q

Describe the cisternal maturation model that describes the golgi apparatus.

A

Says that the cis matures into the medial, and then those mature into the trans

49
Q

Describe the vesicular transport model that describes the golgi apparatus.

A

States that these 3 portions of the golgi are static and their vesicles are replenished as they are used

50
Q

Where can rab-GTP be found? what about Rab-GDP?

A

Rab-GTP: on the vesicle with the cargo in it

Rab-GDP: bound to the GDI?

51
Q

True or false: during docking, the Rab-GTP interacts with the membrane of the target cell before the SNAREs can interact with one another. explain why

A

False:

Rab-GTP interacts with the Rab effector (a tethering protein that extends out from the target cell’s membrane)

THEN the V and T SNARES can interact and form the transSNARE complex

Molecular 2018 (39 decks)

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