L3. Cellular Transport+Lysosomes

Question 1

What are coat proteins

Answer 1

• recruit cargo
• drive vesicle formation
• energy dependent process

Question 2

What are the 3 different coat proteins?

Answer 2

1. COPII: ER
2. COPI: Golgi and ERGIC
3. clathrin: TGN, PM and endosomes

Question 3

State the process of vesicle targeting

Answer 3

1. initiation and cargo selection:GTPase recruits coat proteins and cargo to budding site
2. budding: coat assembles into spherical cage that drives vesicle formation
3. scission: vesicle is released
4. tethering: tethering proteins (Rab GTPases) and other tethering factors target the vesicles to the target membrane
5. docking: SNARES on both vesicles and target membranes engage in fusion
6. fusion: fusing of lipid bilayers between vesicles and targets

Question 4

What are SNARE proteins

Answer 4

alpha helical membrane proteins that drive vesicle fusion

Question 5

How do SNARE proteins assist in vesicle fusion

Answer 5

there is 1 v-sare and 3 t-snares which form coiled coils as they bind together

Question 6

What is membrane traffic

Answer 6

coupled process between exocytosis and endocytosis

-exocytosis adds to the membrane and endocytosis balances it

Question 7

What are the types of endocytosis

Answer 7

1. phagocytosis: engulfing of large matter
2. pinocyotsis: fluid, small vesicles fuses with PM
3. receptor-mediated endocyotsis. ligands bind to receptor on PM and get transported into membrane

Question 8

How are enzymes transported to the lysozyme?

Answer 8

1. proteins are made in the ER and are processed in the golgi - the enzyme is phosphorylated on mannose in cis-golgi face
   2, M6P receptor binds to the phosphorylated enzyme
2. clatharin coat assembles and the vesicle forms and leaves the ER
3. the clatharin coat disocciates and the tethering proteins followed by SNARES binds the vesicle to a late endosome.
4. the lower pH causes the dissociated of the enzymes and receptors, the receptors are returned to the trans golgi
5. the late endosome fuses with the lysosome

Question 9

Describe receptor mediated endocytosis

Answer 9

1. receptors are present on the PM and have ligands bind to it, the clatharin coat forms and buds into cell
2. clatharin uncoats and fuses with early endosomes
3. early endosome fuses with late endosome of lower pH causes the receptor to release the ligand
4. receptors are recycled back to the trans golgi network
5. enzymes are dephosphorylated and transported to the lysosome

Question 10

What are the functions of the lysosome

Answer 10

degrade and recycle cellular components
receive hydrolytic enzymes from the golgu
acidity maintained by proton pumps
degrade material from endocytic pathways

Question 11

What are residual bodies?

Answer 11

material that cannot be degraded by lysosome remain in the lysosome– either get excytose from the cell

Question 12

Tay Sachs

Answer 12

Hex-A deficiency

cannot break down lipid GM2

Question 13

Xanthomas

Answer 13

LDL receptor deficiency on PM- means LDL cannot enter cell and be degraded by lysosomes
-cells cannot uptake LDL to make cholesterol

Question 14

What are the problems posed with lipid trafficking

Answer 14

• hyrdophobic

- may disrupt membrane properties

Question 15

What are the solutions to lipid trafficking?

Answer 15

1. vesicles
2. LTP :protein carriers for lipids
3. membrane contact sites between ER junctions and other organelles

Question 16

What are the 3 different classes of lipids?

Answer 16

1. glycolipids
2. splingolipids
3. sterols

Question 17

Lipid synthesis

Answer 17

• compartmentalized into different organelles

- occurs in the absence of vesicular transport

Question 18

What lipid is synthesized by the mitochondria?

Answer 18

PC: phospatidylcholine

PS->PE->PC: after playing play station, do PE,then started eating fats while playing PC games

Question 19

What lipid is synthesized by the golgi?

Answer 19

sphingolipid (ceramide->splingolipid)

Question 20

What lipid is synthesized in lipid droplets?

Answer 20

cholesterol

oxidbsqualene->lanosterol->cholesterol

Question 21

Lipid Transfer Proteins

Answer 21

(LTPs)

• highly conserved in eukaryotes
• does not have transcellular membranes
• associates with intracellular membranes
• binds lipids and membranes in traget membrane
• has a hydrophobic core to allow lipid to be buried within it.

Question 22

Describe lipid transport by LTPs

Answer 22

free energetic process ( by diffusion)
LTP binds to donor membrane
lipid binds to hydrophobic core with lid that covers it
LTP dissociates from membrane and diffuses to the acceptor membrane
LTP unloads to lipid
LTP returns to donor membrane

Question 23

How is the specificity of the transported lipids determined for LTPs?

Answer 23

class of LTPs and the other proteins and lipids it associates with

Question 24

What are ER junctions

Answer 24

regions where ER comes close with other organelles
10-50nm apart
membranes do not fuse
stable structures

Question 25

What are the functions of the ERJ

Answer 25

-excitation contraction coupling of muscles (allow Ca2+ release from SR )

Question 26

mitochondria ERJ functions

Answer 26

apoptosis
Ca2+ trafficking
PC synthesis

Question 27

What is a tethering protein?

Answer 27

Rab GTPase