Vesicle Trafficking 2

Question 1

5 pieces of key revision. Can membrane proteins flip? Is fusion of vesicles with organelle leaky? In autosomal recessive inheritance which genes on paired chromosome have a defect,?are all proteins in the ER membrane bound? What do SNARES do?

Answer 1

Membrane proteins can’t flip within a biological membrane

Fusion of vesicles with organelle ISN’T leaky

Autosomal recessive inheritance diseases affect BOTH genes on a pair of chromosome

Not all proteins in the endoplasmic reticulum are membrane bound

SNAREs ensure vesicles fuse with the CORRECT target membranes

Question 2

What types of proteins do clathrin, COPI and COPII vesicles have?

Answer 2

They have peripheral proteins.

Their proteins do not embed into the membrane, they can associate BUT also dissociate.

Integral are embedded.

Question 3

Fusion of vesicles with the membrane?

Answer 3

Non leaky

Cytosolic compartments dont move out.

Question 4

Are membranes symmetrical or asymmetrical?

Answer 4

They are asymmetrical

Question 5

Material can move out or back into the endoplasmic reticulum.

What is the process? Where does material move to straight away from the ER? What happens to material that escape the ER?

Note this is NOT talking about vesicles

Answer 5

Material moves out of the ER and goes straight to the GOLGI apparatus

It then can move to the cell surface

If material escapes the ER (As in it doesnt willingly move out as vesicles) then the material can move from the golgi complex back into the ER.

Question 6

What is the process of moving material into the cell towards the ER? What can the early endosome do

Answer 6

This process is endocytosis

When material is taken from outside the cell it moves to the endosome, then to the late endosome (another structure) then to the golgi, then to the endoplasmic reticulum.

The early endosome can recycle material and send it back to the extracellular space instead of sending it to the late endosome

Question 7

Where can the late endosome send material? Instead of sending it to the golgi?

Answer 7

It can send material to lysosomes

Question 8

So movement to and from the endoplasmic reticulum in cells sees retrival of material and recycling.

Where does this occur?

Answer 8

Remember as said before retrival happens from the golgi to the endoplasmic reticulum. This is the retrival of escaped material

Recycling happens at early endosomes.

Question 9

In COPII vesicle formation where do the proteins for the protein coat come from?

Answer 9

They come from the ER. However note, these are packaged into COPII coated vesicles.

Question 10

What is ER translocation? How many proteins mare made by the RER?

Answer 10

ER translocation is the movement of newly synthesised proteins from the cytosol into the endoplasmic reticulum.

1/3 proteins made by the RER

Things like membrane proteins, growth factors, morphogens.

Question 11

What makes the RER good for protein synthesis?

Answer 11

It has lots of ribsomes on its surface which are tightly associated with the ER

Question 12

What does the SER do?

Answer 12

Its important in making lipids and has a smooth outer layer

In comparison the RER makes lots of proteins.

Question 13

How do proteins move from the ribosomes into the RER?

Remember ribosomes are on the outer surface of the RER

Answer 13

They move into the RER from the ribosomes by co translational translocation.

Question 14

What is post translational translocation? Difference between co translational translocation

Answer 14

This is when proteins are made in the cytoplasm

These are then translated on ribosomes away from the RER

These proteins are then folded (by chaperones) and are then moved into organelle (Which doesnt include the endoplasmic reticulum)

Question 15

What is common of proteins associated with the endoplasmic reticulum’s outer membranes?

Answer 15

They are co translationally translocated

Question 16

What are ribosomes important for? What is translocation?

Answer 16

Translation of proteins.

Translocation is movement! Such as the movement of proteins.

Question 17

How do proteins get into the ER? What is the signal hypothesis?

Answer 17

They need a signal

The proteins need a series of amino acids on them which allows the to bind to the ER., through signal peptidase. This signal allows them to be translocated from the cytoplasm into the lumen of the endoplasmic reticulum.

Signal hypothesis:
If a protein has a series of amino acids encoding an ER signal, such as a signal sequence, it can be translated and translocated into the ER.

So note proteins made outside of the ER move into the ER by their signal sequences binding to the cleaved signal peptidases on the ER. The proteins polypeptide chains then move into the ER

Question 18

So what is the sumamry of movement of proteins from the cytoplasm into the ER

Answer 18

These proteins have a signal sequence

This signal sequence binds to a signal peptidase on the the endoplasmic reticulum surface

This signal sequence can then be cleaved off of the protein

This allows the protein into the ER

Question 19

What is the typical feature of the proteins that enter the endoplasmic reticulum via pepitidases? What happens to these proteins once they’re inside the ER?

Answer 19

They are soluble proteins

Once they are inside of the ER they need to be folded by the help of chaperones in the ER

Question 20

Whats the difference between ptoteins synthesised by ribosomes away and from the RER and at the RE?

Answer 20

Proteins at the ER arent yet folded. They must move into the ER to be folded

They are described as soluble molecules

Proteins synthesised away from the ER by ribosomes do get folded

Question 21

What is the hole in the ER which lets proteins through?

Answer 21

This is called a translocator.

This can be opened with the help of a polypeptide

Question 22

Why is important that the hole proteins use to enter the RER has a flap?

Answer 22

This allows it to be closed. This is because the inside of the ER is different to the environment outside of the ER.

Question 23

Features of the translocator in the ER (the hole)

Answer 23

There is no leakage through the translocator (hole)

The translocator is either in the closed or open state

This allows the signal sequence to embed and feed through

This allows a protein (made on by the ribosomes on the RER) are able to move inside of the RER via co translational translocation

Question 24

Note - transmembrane proteins move into the CELL membrane (not ER) by the same mechanism that soluble proteins (made on ribosomes assoicated with the RER) do

However only part of the transmembrane protein moves into the CELL MEMBRANE

So how are transmembrane proteins anchored into the CELL MEBRANE?

Answer 24

You have a DOMAIN on the transmembrane protein which moves into the ER

The protein binds to the translocator hole of the ER in order to move in

The domain on the protein acts as a stop transfer sequence, this stops signals to the translocator to close over and not allow the transmembrane in

However at a certain point this domain is cleaved off by a signal peptidase. This means that the hole doesnt let anymore transmembrane proteins through.

This allows the transmembrane protein to be anchored into the membrane and it can’t move out.

Half of the protein gets stuck inside the CELL MEBRANE and half gets stuck outside

Question 25

Type one membrane protein?

Answer 25

This has its n terminus located in the extracellular (So outside of cell MEMBRANE)

Question 26

Type two transmembrane protein

Answer 26

Has its C terminus extracellular (so outside the CELL MEBRANE)

The orientation of type one membrane protein is reversed

Question 27

How do we get multiple Transmembrane proteins?

Answer 27

This is by having lots of stop start sequences on proteins which enter the cell membrane

Question 28

How do membrane proteins fold? Give on example of what folds the membrane protein?

Remember membrane proteins move from inside of the cell to the membrane. They dont come from outside of the cell.

Answer 28

The lumen of the ER is rich in chaperones

These ensure proteins fold. BIP is a specific chaperone example

Question 29

How is the chaperone BIP related to folding antibodies? And how do these antibodies move out of the ER

Answer 29

Within the ER there lots of these BIP chaperones

BIP associates with newly formed antibody molecules in cells

It helps to fold them so they have a specific arrangement

It ensures the antibodies stay in the lumen of the ER, until they are completely assembled

When they’re assembled correctly they can be packaged into transport vesicles and sent through secretory pathways

Question 30

Defects in folding proteins? Cysstic fibrosis example? And what does a new drug hope to do?

Answer 30

Chloride channel proteins are misfolded

The delta fibroid is misfolded so gets stuck in the ER. This means you dont get any channels in the cell surface, you get all the symptoms of cystic fibrosis

A new drugs? Orkambi
Helps to deliver the delta fibroid channel to the cell surface AND increase the liklihood that the channel opens

Note this channel protein doesnt work as well as the wild type version

Question 31

What is the unfolded protein response?

Answer 31

If the cell makes alot of unfolded proteins, they upregulate the unfolded protein response.

This increases number of ER chaperones and decreases protein syntheiss

This ensures high quality folding in cells

Question 32

What is Gauchers disease?

Answer 32

This leads to mutations in lysosomal enzymes required for glucosylceramide metabolism

This can be treated with drugs that activate the unfolded protein response

Question 33

Emphesemya?

This is a misfolding disease

Answer 33

This is the deficiency of secretion of alpha 1 antitrysin

This is also the failure to inactive neutrophil elastase in the lungs. This breaks down the ECM and makes the lungs permeable

It can be treated by enzyme replacement therapies

This helps proteins to be properly folded

Question 34

Liver damage caused by mutant unfolded protein?

Answer 34

The liver may not degrade this mutated protein and it thus accumulates in hepatocytes.

Question 35

Hypothyroidism cause and effect?

This is another misfolded protein condition

Answer 35

This leads to the production of mutant thyroglobulin, which results in massive proliferation of the ER in attempt to secrete correct amounts of hormones.