Intracellular Membrane Traffic

Question 1

What is the secretory pathway?

Answer 1

Delivers new proteins, carbs, lipids, etc to extracellular space or plasma membrane. Exocytosis

Question 2

Where do cells move plasma membrane components to in endocytosis?

Answer 2

Endosomes (endocytotic pathway)

Question 3

Where can cells bring stuff from endosomes?

Answer 3

Lysosome (degradation) or rest of the cell

Question 4

Where does the secretory pathway start and where does it move towards?

Answer 4

Starts in ER, goes out to golgi and cell surface (side route to lysosomes)

Question 5

What’s the role of retrieval pathways?

Answer 5

Balance membrane flow (same # of lipids in sending / receiving areas)

Question 6

How do vesicles know where to go?

Answer 6

Specific combination of molecular markers on cytosolic surface of membranes to differentiate them

Question 7

What are vesicle coats for?

Answer 7

Getting specific molecules and going too specific places

Question 8

What are the three types of coats on vesicles?

Answer 8

COP1, COPII, and Clathrin

Question 9

Which vesicle coat buds from Golgi compartments?

Answer 9

COP1

Question 10

Which vesicle coat buds from ER?

Answer 10

COPII

Question 11

Which vesicle coat transports stuff from the plasma membrane and between endosomal/golgi compartments?

Answer 11

Clathrin

Question 12

What are Clathrin subunits called? Where are they?

Answer 12

triskelions, outer coat

Question 13

What type of proteins are on the inner layer of the clathrin coat?

Answer 13

Adaptor proteins

Question 14

What are cargo receptors?

Answer 14

Transmembrane receptors that capture soluble cargo molecules inside the vesicle. Adaptor proteins trap them

Question 15

How many subunits to the best characterized adaptor proteins have?

Answer 15

4; others are single chain

Question 16

What is the purpose of multiple types of adaptor proteins?

Answer 16

To be specific for a different set of cargo receptors

Question 17

What are the light chains of a triskelion for?

Answer 17

Link to the actitn cytoskeleton, generating force for membrane budding / vesicle movement. Phosphorylation regulates coat assembly

Question 18

What are heavy chains of triskelions for?

Answer 18

Fom an outer shell that binds to adaptor proteins

Question 19

What on the membrane do adaptor proteins bind to? Why?

Answer 19

Phosphoinositides (lipids). So that cargo receptors can come bind

Question 20

What gives phosphoinositols their name?

Answer 20

They’re phospholipids with inositol sugars at the top

Question 21

How are PIPS regulated?

Answer 21

Phosphorylation / dephosphorylation by kinases / phosphatases

Question 22

What assembles at bud necks as clathin-coated buds grow?

Answer 22

Dynamin

Question 23

What on Dynamin regulates how fast vesicles pinch off from the membrane?

Answer 23

Its GTPase domain

Question 24

How is Dynamin recruited?

Answer 24

PIPs in the neck

Question 25

What happens to the clathrin coat when a vesicle is leaving the membrane?

Answer 25

Vesicle loses the clathrin coat

Question 26

What enzymes regulate coat formation?

Answer 26

Coat-recruitment GTPases

Question 27

What turns coat-activating GTPases on and off?

Answer 27

On = guanine nucleotide exchange factors (GDP\>GTP) Off = GTPase-activating proteins (GTP\>GDP, hydrolysis)

Question 28

Which type of coat assembly is Sar1 responsible for?

Answer 28

Assembly of COPII at ER

Question 29

If coats aren't dissasembled by the time they get to their target membrane (and SAR1 is still bound) what happens?

Answer 29

Kinases phosphorylate the coat proteins, and coat disassembly is completed. Coats need to be gone before fusion

Question 30

What is the function of Rab proteins and Rab effectors?

Answer 30

Guide vesicles to the right place once they leave their original membrane

Question 31

What is the function of SNARE proteins and SNARE regulators?

Answer 31

Mediate fusion of lipid bilayers

Question 32

What type of protein is Rab

Answer 32

Monomeric GTPase (it has one subunit and binds GTP)

Question 33

Where are Rab proteins?

Answer 33

On transport vesicles, on target membranes, or on both

Question 34

How are Rab proteins activated?

Answer 34

Bind to GTP, makes them insoluble in cytosol and bind to membrane of organelle or transport vesicle

Question 35

What is the function of Rab effectors?

Answer 35

Grab GTP-activated Rab proteins

Question 36

Why are SNARE proteins needed?

Answer 36

Water needs to be displaced from hydrophilic surface of membrane for membranes to fuse - this is energetically unfavorable

Question 37

Where are v- and t-SNARES found?

Answer 37

v-snares = vesicle membranes t-snares = target membranes

Question 38

How do v-SNARES and t-SNARES bind together?

Answer 38

Helical domains on each protein wrap around each other

Question 39

How are interacting SNARES pried apart for reuse?

Answer 39

NSF cycles bewteen membranes and cytosol, catalyzes disassembly

Question 40

What pH are lysosomes? Why?

Answer 40

Low (5.0, about 2 lower than cytoplasm). So that hydrolytic enzymes can activate and eat things. Protect lysosomes from damaging cells (enzymes that leak out are inactivated at lower pH)

Question 41

After macromolecules are digested in lysosomes, what happens to their useful products (amino acids, sugars, nucleotides)?

Answer 41

Transport proteins in lysosome membrane carry them to the cytosol

Question 42

How does H+ get into lysosomes to keep pH low?

Answer 42

vacuolar h+ ATPases pump protons in

Question 43

What happens when late endosomes and newly synthesized lysosomal hydrolases fuse?

Answer 43

Form endolysosomes, which fuse with each other to become lysosomes

Question 44

Which lysosome degradation pathway specializes in nonspecific uptake of fluids / membrane particles attached to the plasma membrnae?

Answer 44

macropinocytosis

Question 45

What is the benefit of autophagy over other forms of degradation (e.g. proteosomes)?

Answer 45

Autophagy can remove large objects from the cell

Question 46

How are autophagosoes formed? What happens after it's formed?

Answer 46

Double membrane surrounds cargo, then it merges with lysosome for degradation

Question 47

What happens to endocytotic vesicles after they enter the membrane?

Answer 47

Fuse with the early endosome

Question 48

What types of pinocytic vesicles form lipid rafts and originally were recognized by their ability to transport molecules across endothelial cells?

Answer 48

Caveolae

Question 49

How do most aniaml cells take up cholesterol into the cell?

Answer 49

Receptor-mediated endocytosis

Question 50

How do LDL's get into the cell? What are they for?

Answer 50

Transmembrane receptors grab them and they get inserted. For getting cholesterol for membrane synthesis.

Question 51

What do LDL receptors transport while they're still going to the lysosome?

Answer 51

Cholesteryl ester. Turns into cholesterol in the lysosome