Transport of Macromolecules

Question 1

What are macromolecules?

Answer 1

Larger molecules (proteins, pathogens)

Question 2

What is exocytosis?

Answer 2

• Excretion/secretion of large molecules out of cell, across cell membrane into extracellular space
• Allows transport of membrane proteins from Golgi to cell surface

Question 3

What are 2 types of exocytosis?

Answer 3

1. Constitutive

2. Regulated

Question 4

Where does constitutive exocytosis occur?

Answer 4

In all cells, all the time

Question 5

What method is used to move plasma membrane proteins from Golgi apparatus to cell surface?

Answer 5

Constitutive exocytosis

1. Vesicles bud off Golgi and move to plasma membrane
2. Fuse with plasma membrane and are secreted

Question 6

Where are proteins destined to be secreted from the cell translated?

Answer 6

On ribosomes attached to the RER

Question 7

What is regulated exocytosis?

Answer 7

• Only occurs in specialised cells (e.g. neuronal cells, pancreatic cells)
• Ca2+ dependent

Question 8

How does regulated exocytosis occur?

Answer 8

Vesicles from Golgi will only fuse with cell membrane when they receive a signal –> usually in form of Ca2+

Question 9

Describe regulated exocytosis in nerve terminal

Answer 9

1. Synaptic vesicles containing neurotransmitters wait for signal
2. Nerve stimulation leads to depolarisation of cell resulting in action potential that travels along axon to nerve terminal
3. Depolarisation activates voltage-gated ion channels that allow Ca2+ to rapidly enter nerve terminal
4. Ca2+ allows vesicles to fuse with synaptic membrane and release their contents into synaptic cleft

Question 10

What is endocytosis?

Answer 10

Ingestion/uptake of extracellular macromolecules across the plasma membrane into the cell

Question 11

What are the 3 processes involved in endocytosis?

Answer 11

1. Phagocytosis
2. Pinocytosis
3. Receptor-mediated endocytosis

Question 12

What is pinocytosis?

Answer 12

‘Cell drinking’ - uptake of fluid (cell samples fluid by taking it into cytoplasm via vesicle)

Question 13

What is phagocytosis?

Answer 13

Ingestion of large particles by specialised cells

1. Cell ingests pathogen
2. Fuses with lysosome and then digests pathogen through enzymes
3. Remnants are displayed on cell surface of phagocyte –> alerts other immune cells
4. Utilisable material transported into cytosol
5. Indigestible material remain in lysosomes are residual bodies

Question 14

What is receptor-mediated endocytosis?

Answer 14

Selective uptake of macromolecules from extracellular fluid via clathrin-coated pits and vesicles

Involves receptor recognition of ligands

Question 15

Describe process of receptor-mediated endocytosis?

Answer 15

1. Ligand binds to specific cell surface receptor (integral membrane protein)
2. Receptor-macromolecule complex accumulates in a clathrin-coated pit and then endocytose in a clathrin-coated vesicle
3. Receptor recycled

Question 16

Give example of receptor-mediated endocytosis

Answer 16

Cholesterol uptake (LDL receptor)

Question 17

What are the professional phagocytes?

Answer 17

1. Macrophages
2. Neutrophils
3. Dendritic cells