M&R Session 6- Principles Of Receptor- Mediated Endocytosis

Question 0

What mechanism is used in phagocytosis?

Answer 0

Membrane zippering.

Question 1

Define phagocytosis

Answer 1

The internalisation of particulate matter.

Question 2

What is pinocytosis?

Answer 2

The internalisation of plasma membrane to form a vesicle.

Question 3

What does pinocytosis allow the uptake of?

Answer 3

Extracellular solutes

Question 4

What is endocytosis?

Answer 4

The selective internalisation of molecules by binding to specific cell surface receptors.

Question 5

What does cholesterol have to be packaged in?

Answer 5

LDLs

Question 6

Describe the components of an LDL

Answer 6

Core- esterified cholesterol esters

Lipid monolayer- phospholipids, cholesterol and apoB

Question 7

In cholesterol RME, where are LDL receptors clustered?

Answer 7

Over coated pits

Question 8

What happens to the coated pits

Answer 8

They invaginate and pinch off from the plasma membrane to form coated vesicles

Question 9

What happens to the coated vesicles?

Answer 9

They are quickly uncoated

Question 10

What happens to the uncoated vesicles?

Answer 10

They bind with larger smooth vesicles called endosomes

Question 11

What pH is the endosome maintained at?

What maintains it?

Answer 11

5.5-6

ATP- dependent proton pump

Question 12

What happens due to the pH of the endosome?

Answer 12

The LDL receptor has low affinity for the LDL so they dissociate

Question 13

What is the endosome known as?

Answer 13

Compartment for Uncoupling of Receptor and Ligand (CURL)

Question 14

What happens to the receptor and LDLs in the endosome after dissociation? (2)

Answer 14

The LDL receptors bud off in a vesicle and are returned to the plasma membrane.
The LDLs are budded of in a vesicle and fused with the lysosome so that the cholesterol can be hydrolysed from the esters and released into the cell.

Question 15

What are coat structures called and made up of?

Answer 15

Triskeletons

Clathrin and two light chains

Question 16

Do clathrin coated pits from spontaneously?

Answer 16

Yes

Question 17

What uncoates clathrin coated vesicles?

Answer 17

ATP dependent in coating protein

Question 18

What happens to the ligand and receptor in cholesterol RME?

Answer 18

Ligand- degraded

Receptor- recycled

Question 19

Describe RME of Fe3+ ions

Answer 19

• 2 Fe3+ ions bind to apotransferrin to form transferrin
• transferrin binds to transferrin receptor on coated pit and is internalised as cholesterol example.
• Fe3+ ions are released at acidic endosome, leaving apotransferrin attached to receptor.
• apotransferrin-receptor complex is recycled to plasma membrane and dissociate as neutral pH again.

Question 20

What happens to the ligand and receptor in Fe3+ RME?

Answer 20

Ligand- recycled

Receptor- recycled

Question 21

What is the fate of the ligand and receptor in insulin RME?

Answer 21

Both are degraded

Question 22

What does the insulin mechanism allow for?

Answer 22

Reduction in number of insulin receptors at cell surface- down regulation

Question 23

What is the fate of the ligand and receptor in transcytosis of immunoglobulin?

Answer 23

Ligand and receptor are transported

Question 24

How do membrane-enveloped viruses and toxins exploit endocytic pathways?

Answer 24

They bind to receptors on plasma membrane, and once in the endosome, they fuse with the endosomal membrane and release their RNA into the cell which can be translated to give more viral particles.