Vesicular Transport

Question 1

Where do membrane bound vesicles carry cargo?

Answer 1

In their lumen

Question 2

Vesicles carry cargo from a _______ to a _______ compartment.

Answer 2

Donor

Recipient

Question 3

Where do vesicles bud from?

Answer 3

Specialised coated regions of the donor compartment

Question 4

Where are vesicles coated in COPII travelling from and to?

Answer 4

ER to golgi

Question 5

Where are vesicles coated in COPI travelling from and to?

Answer 5

Golgi to ER

Question 6

Where are vesicles coated in Clathrin travelling between?

Answer 6

Golgi, lysosomes and the plasma membrane

Question 7

What is the structure of a clathrin subunit?

Answer 7

3 large and 3 small polypeptide chains which form a 3 legged triskelion structure

Question 8

How do the individual subunits interact to form clathrin?

Answer 8

triskelions create a basket like framework of pentagons and hexagons

Question 9

Which side of the membrane is clathrin found on?

Answer 9

The cystolic side

Question 10

What is adaptin?

Answer 10

A protein complex which attaches clathrin to the membrane as well as interacting with transmembranous proteins

Question 11

What is dynamin?

Answer 11

A protein which binds in a ring to the neck of a vesicle allowing it to pinch off

Question 12

What do vesicles have on their surface which identifies the cargo and origin of the vesicle?

Answer 12

V-snare proteins

Question 13

Where are complementary receptors (of vesicle surface proteins) found?

Answer 13

On the target membrane

Question 14

What are v-snare proteins complementary receptors called?

Answer 14

T-snare proteins

Question 15

What happens when v and t snares meet?

Answer 15

They wrap around each other forming a stable trans-snare complex which locks the two membranes together

Question 16

How many different pairs of snares are there?

Answer 16

20

Question 17

What is exocytosis?

Answer 17

Secretion from the cell

Question 18

Where do the molecules that are secreted go?

Answer 18

Into the extracellular matrix

To the plasma membrane

Question 19

Why would a protein that has entered the golgi not be secreted?

Answer 19

If it is returned to the golgi
If it is retained in the golgi
If it is directed to another organelle

Question 20

What are the different pathways in which a molecule can be excreted from the cell?

Answer 20

Constitutive pathway

Regulated secretory pathway

Question 21

Which is the default pathway for exocytosis?

Answer 21

Constitutive pathway

Question 22

Describe the process of a protein being exocytosed in the constitutive pathway.

Answer 22

1. The vesicle buds from the golgi
2. The vesicle is headed to the plasma membrane
3. The vesicle fuses with the plasma membrane immediately
4. The vesicle contents is exocytosed

Question 23

Describe the process of a protein being exocytosed in the regulated secretory pathway.

Answer 23

1. The vesicle buds from the golgi
2. The vesicle is headed to the plasma membrane
3. The vesicle only fuses with the plasma membrane once a signal is received
4. The vesicle contents is exocytosed

Question 24

What type of proteins are exocytosed in the secretory pathway?

Answer 24

Secretory proteins

Question 25

What does the regulated secretory pathway allow for?

Answer 25

Storage of secretory proteins
Further processing of the protein
Release of the protein in response to a trigger

Question 26

Why is storage of secretory proteins important in the regulated secretory pathway?

Answer 26

Because it protects the cells from substances that may be harmful to it - hydrolytic enzymes

Question 27

Why is further processing of secretory proteins important in the regulated secretory pathway?

Answer 27

Because some proteins are synthesised in inactive forms and therefore can be activated before being exocytosed

Question 28

What is proteolysis?

Answer 28

The modification of proteins by breaking them down into smaller polypeptides or amino acids

Question 29

What might vesicles do whilst waiting for a signal to exocytose their contents?

Answer 29

‘Dock’ with the plasma membrane but not fuse

Question 30

Give three examples of substances that might be exocytosed from a cell in response to a signal.

Answer 30

Digestive enzymes in response to food in the gut
Insulin in response to high blood glucose levels
Histamine in response to the presence of antigens

Question 31

What is endocytosis?

Answer 31

Uptake into a cell

Question 32

When must the extra components found in the plasma membrane by removed and recycled?

Answer 32

After exocytosis because the surface area is increased

Question 33

What does the endocytotic-exocytotic cycle do?

Answer 33

Keep a balance between secretion and internalisation

Question 34

What percentage of the plasma membrane is clathrin coated pits?

Answer 34

2%

Question 35

Explain the process of pinocytosis.

Answer 35

1. Clathrin coated pits rapidly invaginate and form vesicles
2. Vesicles lose their coat and fuse with early endosomes
3. Any extracellular constituents that have been taken up can be delivered to lysosomes for digestion

Question 36

What substances are absorbed during receptor-mediated endocytosis?

Answer 36

Only receptor-specific substances
Proteins
Hormones
Metabolites

Question 37

Explain the process of receptor-mediated endocytosis.

Answer 37

The plasma membrane invaginates forming a vesicle containing the absorbed substance which then buds off

Question 38

Explain the process of phagocytosis.

Answer 38

1. Specialised white blood cells take up large particles (microorganisms, dead cells, cell debris)
2. The particle binds to the surface of the phagocyte and is recognised by cell surface receptors
3. The cell extends pseudopods which engulf the particle forming a large endocytotic vesicle = phagosome
4. The phagosome fuses with a lysosome and its contents is digested