Protein sorting

Question 1

Some organelles have a doubled bilayer, which ones?

Answer 1

Nucleus, mitochondria & chloroplast

Question 2

Which are the three kinds of protein sorting?

Answer 2

Gated transport, transmembrane transport & vesicles

Question 3

Describe the gated transport.

Answer 3

Cytosol in/out of nucleus, bidirectional
Gated transport through nuclear pores
NPC - nuclear pore complex
Nuclear transport receptors (importins/exportins)
Direct the cargo to the pore by interacting with nuclear pore fibrils
Follows the cargo to its right position

Question 4

Describe the transmembrane transport.

Answer 4

Cytosol into ER, mitochondria, chloroplasts, peroxisomes, unidirectional.

Proteins enter the ER —> synthesised by ribosomes
Two types of proteins produced in ER:
Soluble proteins entering the ER lumen
Transmembrane proteins retained in the ER membrane

Question 5

What two types of proteins are produced in the ER?

Answer 5

Soluble proteins & transmembrane proteins

Question 6

Describe the transport through vesicles.

Answer 6

Between endomembrane systems (ex, ER —> Golgi)
Transport by vesicles, of proteins, lipids, brane proteins

Question 7

Describe the exocytosis.

Answer 7

Delivery of protein/lipids/carbohydrates
Protein modification in the ER: disulphide bond-formation, glycosylation
ER exit is controlled to ensure protein quality, chaperons help unfinished proteins to fold correctly
Protein exits the cell in two different ways: constitutive secretion (unregulated fusion) & regulated secretion (signal transduction)

Question 8

Describe the endocytic pathway.

Answer 8

Transport –> ER

Uptake of fluids/molecules from the external environment, endocytic vesicle is pinched off
Two types of endocytosis: Pinocytosis (cellular drinking) & Phagocytosis (cellular eating)

Question 9

Name some of the coated vesicles.

Answer 9

Clathrin - transport from golgi/plasma membrane
COPII - transport from ER/golgi cisterna
COPI - transport from ER/golgi cisterna

Question 10

What happens at the vesicles docking?

Answer 10

2 T-SNAREs coil together –> hemifusion

Question 11

Describe the sorting of receptors (in endosomes)

Answer 11

1. Recycling - return to the plasma membrane
2. Lysosome - for degradation
3. Transcytosis - redirected to another part of the plasma membrane