More membrane trafficking

Question 1

What are COPII vesicles made up of?

Answer 1

Sar1 GTPase
COPII coat
Carries newly synthesised proteins

Question 2

What des COPI move through the golgi?

Answer 2

Newly synthesised proteins and retreived proteins. These are moved in an anterograde and retrograde direction

Question 3

Where are proteins usually coated by clathrin

Answer 3

Newly made lysosomal proteins at the TGN
Most material taken up by endocytosis

Question 4

Describe cranio-lenticulo-sultural dysplastia

Answer 4

Caused by a mutation in SEC23A, causing abnormal ER to golgi trafficking
Musculoskeletal issues
May have been issues with secretory pathway delivering collagen to the ECM

Question 5

What do SEC23A and SEC24 bind to, regardless of wild type of mutant?

Answer 5

GTP1

Question 6

How does COPII package procollagen (300-400nm)?

Answer 6

COPII vesicles are 60-80nm diameter
The COPII coat sorts procollagen into tubular structures which are modified for large cargo sorting

Question 7

Describe the Rab family of GTPases

Answer 7

Member of the Ras superfamily
Cycles between membrane and cytosol
Involved in membrane and vesicular trafficking
Originally identified for being active in a vesicle-SNARE fusion

Question 8

How do Rab-GTPs work in vesicles?

Answer 8

Recruit tethering proteins which wiggle into cytoplasm from the membrane to dock to the vesicle. This promotes SNARE assembly

Question 9

What cascades allow cargo to move between organelles?

Answer 9

Rab cascades
Cargo moves from a Rab5 to Rab7 compartment

Question 10

What can a missense of Rab7a lead to?

Answer 10

Charcot-Marie-Tooth 2B
Excessive activation
Reduced autophagic flux
Premature neurotrophine receptor degradation
Inhibition of neurite outgrowth

Question 11

How does Legionella pneumophila utilise Rab1?

Answer 11

It creates an ER-like compartment

Question 12

What is the role of the smooth ER

Answer 12

Site of lipid synthesis
Role in calcium storage

Question 13

Describe the inter membrane contact site between ER and microtubules

Answer 13

The ER forms a loop around mitochondria with its tubules

Question 14

Is there evience of the ER fusing with organelles?

Answer 14

No, it only has only contact sites

Question 15

What is CLEM?

Answer 15

Correlative light and electron microscopy.
Allows fluorescence to be identified and correlated with EM.
This shows an ultrastructure not shown in light microscopy

Question 16

What is tomography?

Answer 16

Imaging using a penetrating wave to build up 3D models of organelles.

Question 17

Describe some features of membrane contact sites

Answer 17

Ribosomes are excluded
Membranes are very close together (10-80nm)
ER contacts can be short or long-lived

Question 18

What proteins link two membranes together?

Answer 18

Tethers

Question 19

Describe tethers

Answer 19

Can be protein-protein or protein-lipid
Around 30nm
Inhibit fusion
Has a defined lipid proteome

Question 20

What tether transfers cholesterol?

Answer 20

Oxysterol binding protein (OSBP)
This is raft-like

Question 21

What do tethers provide platforms for?

Answer 21

Calcium mobilisation
Lipid transfer
Signalling
Organelle division

Question 22

How much calcium is there in the ER lumen compared to cytosol?

Answer 22

Cytosol- 0.1μm
ER lumen- 60-500μm
This is due to calcium taken up by the endocytic pathway

Question 23

What is the Stim1 receptor?

Answer 23

TM calcium sensor in the ER
Monomeric under resting conditions
When calcium levels fall, Stim1 is oligomerised

Question 24

What does oligomerised Stim1 interact with on the plasma membrane?

Answer 24

Ora1 channel
This is abundant in plasma membrane rich in PIP2

Question 25

How is cholesterol moved to plasma membranes?

Answer 25

Cholesterol sensors in the ER switch on its synthesis. LDL receptors take cholesterol, move through the endocytic pathway and are broken down in lysosomes, releasing free cholesterol

Question 26

What proteins move cholesterol through the cytosol?

Answer 26

Lipid transfer proteins (LTPs). Hydrophobic grooves to protect from the hydrophbic environment of the cytosol
Move along concentration gradients of lipids or ions

Question 27

Describe Niemann Pick C disease

Answer 27

Mutation in a TM protein important in contact sites.
Lipids accumulate in spleen, liver, lungs, bone marrow and brain
Sphingomyelin accumulates in lysosomes

Question 28

How are membrane contact sites involved with organelle fission?

Answer 28

ER surrounds fission enzymes acting on enzymes
MCSs interact these interactions

Question 29

Describe 2 diseases associated with MCS

Answer 29

TDP-43 is linked to ALS and regulates ER-mitochondria contacts
REEP1 is associated with hereditary spastic paraplegia, leading to disruption of the ER mitochondria contacts