Protein trafficking 3

Question 1

How can proteins be selectively recruited into buds?

Answer 1

Some integral proteins may have cytoplasmic domains that interact with coat proteins that will concentrate them into buds.

Question 2

How can lumenal cargo proteins be selectively recruited into buds?

Answer 2

They can interact with cargo receptors that span the ER membrane and interact with coat proteins.

Question 3

What proteins may be excluded from entering budding vesicles?

Answer 3

Those that mis-fold in the ER.

Question 4

How does the ER act as a quality control station in the secretory pathway?

Answer 4

Certain molecules need to be correctly assembled before they can enter ER transport vesicles, such as antibodies.

Question 5

What is the function of BiP in antibody formation?

Answer 5

It keeps the immunoglobin from entering the ER exit when it is not fully assembled.

Question 6

What is retrograde transport?

Answer 6

When proteins are returned to the ER after originally being transported from the ER to the golgi.

Question 7

Where is a KDEL sequence found?

Answer 7

At C-termini.

Question 8

What makes up KDEL?

Answer 8

Lysine, Aspartic acid, glutamic acid and leucine.

Question 9

How can proteins undergo retrograde transport?

Answer 9

KDEL containing proteins are recognised by KDEL receptors (transmembrane proteins) and are selectively packaged into COPI coated vesicles for retrograde traffick back to the ER.

Question 10

How can the KDEL receptor be reused?

Answer 10

When in the ER, the KDEL receptor releases the protein and can return to the Golgi in COPII vesicles.

Question 11

How does a vesicle know the correct membrane to fuse with?

Answer 11

Rab’s and SNARE proteins give vesicles and target membranes a molecular identity. Fusion can only occur if the molecular identities of the two membranes are compatible.

Question 12

What is the difference between tSNAREs and vSNAREs?

Answer 12

tSNAREs = target SNARE proteins, vSNARE = vesicle SNARE proteins.

Question 13

What is the specific way in which the two SNARE proteins interact?

Answer 13

The pairing brings the membranes together and forces them to fuse. The SNAREs coil around each other.

Question 14

What is a fusion pore?

Answer 14

A channel through which secretions are released from the vesicle to the cell exterior.

Question 15

What are the intermediates before the formation of a fusion pore?

Answer 15

Stalk and hemifusion.

Question 16

How does botox work?

Answer 16

It cleaves SNARE proteins so that neurotransmitter vesicles cannot fuse with the plasma membrane. This causes paralysis.

Question 17

What is an example of protein modification?

Answer 17

Glycosylation.

Question 18

Where does N-linked glycosylation occur?

Answer 18

In the ER.

Question 19

Where do O-linked modifications occur?

Answer 19

In the Golgi.

Question 20

What transfers the oligosaccharide from the lipid to the protein?

Answer 20

Oligosaccharyl transferase.

Question 21

How does N-linked glycosylation occur?

Answer 21

Sugars are transferred from dolichol (which is a lipid) onto proteins containing NXS/T sequences in the lumen of the ER.

Question 22

What does the golgi do?

Answer 22

Further modification of oligosaccharides and protein.

Question 23

What is the difference between the cis and trans golgi stacks?

Answer 23

Cis receive vesicles from the ER and trans package vesicles for delivery to the plasma membrane.

Question 24

What is the difference beteen constitutive secretion and regulated secretion?

Answer 24

Regulated secretion involves a signal such as hormones/neurotransmitter causing the secretion of vesicles.

Question 25

Give some examples of hydrolases found in lysosomes.

Answer 25

Nucleases, proteases, glycosidases and sulfatases.

Question 26

How is the lumen of the lysosome kept acidic?

Answer 26

There is a proton pump that hydrolyses ATP to ADP and Pi.