Cell: secretory pathway

Question 1

What are 2 key enzymes involved in phospholipid synthesis?

Answer 1

Scramblase
Energy-dependent flippase

Question 2

What is the role of scramblase?

Answer 2

equilibrates lipids (makes sure leaflets are same size)

Question 3

What is the role of energy-dependent flippase?

Answer 3

ensures membrane asymmetry is maintained

Question 4

Describe the ER

Answer 4

• Dynamic network that is continuously breaking and reforming
• Connected to the nuclear envelope
• Forms hollow tubes and flattened sacs → chambers are cisternae
• rough (ribosomes)
• smooth

Question 5

What are the functions of the ER?

Answer 5

Quality control
Synthesis
Storage (e.g antibodies - IGM)
Detoxification e.g SER in liver

Question 6

Describe how the RER is used for quality control.

Answer 6

• Newly made membrane and secreted proteins need to be translocated into the ER
• Ribosome sits tightly on the pore = no leakage as ionic conc. in lumen is v diff to the cytosol
• Chaperone proteins (e.g BiP) help newly synthesised linear sequences of amino acids to fold correctly into tertiary and quaternary structures
• Ensures only properly folded proteins move through the secretory pathway

Question 7

In the RER, why does the ribosome need to sit tightly on the pore?

Answer 7

To ensure there’s no leakage as the ionic conc. in the ER lumen is v diff to the cytosol

Question 8

What are the roles of the SER?

Answer 8

• Phospholipid and cholesterol synthesis
• Steroid hormone production
• Synthesis and storage of glycerides
• Synthesis and storage of glycogen
• Important role as a calcium store

Question 9

An overload of which ion can cause pancreatitis?

Answer 9

Ca++ overload
Alcohol / biliary disease
Aberrant activation of intracellular trypsin
Vascularisation and necrosis
Failure to maintain Ca+ homeostasis in part due to failure of Ca++ pumps at the PM

Question 10

How are materials transported between the ER and Golgi?

Answer 10

Vesicles and tubules
- vesicles bud (high SA:V) off the ER and are recieved by the Golgi
= lipid asymmetry mainitained and no cargo leakage

Question 11

Describe the coating of vesicles

Answer 11

• Cage of specialised (peripheral membrane) proteins
• Aid the formation of the vesicle
• 3 types: Clathrin, COPI, COPII

Question 12

Why are vesicle coats discarded before it fuses with target compartment?

Answer 12

To reveal recognition proteins (SNARE proteins)

Question 13

Describe SNARE proteins

Answer 13

→ soluble N-ethylmaleimide sensitive factor adaptor protein receptor
- Transmembrane domain
2 types
v-SNARE = found in vesicle membrane
t-SNARE = found in target membrane

Question 14

Describe the golgi apparatus

Answer 14

• Made up of flattened discs (cisternae)
• A typical Golgi will consist of 5-6 cisternae
• Diff cells have diff numbers of Golgi
• Tends to lie near the nucleus
• Communicate with the ER and cell membrane through vesicles and tubules

Question 15

Describe the functions of the golgi

Answer 15

Modification and packaging of secreted proteins
Renewal and modification of the plasma membrane
Delivery of material to other organelles → especially endocytic pathway

Question 16

Vesicles from the ER bind to the ___ face of the golgi.

Answer 16

Vesicles from the ER bind to the cis face of the golgi.

Question 17

Vesicles from the ER are processed and excreted from the ___ face of the golgi.

Answer 17

Vesicles from the ER are processed and excreted from the trans face of the golgi.