Receptor Mediated Endocytosis

Question 1

Is the uncoating of a clathrin coat spontaneous or need ATP?

Answer 1

Needs enzymes which are ATP dependent

Question 2

How does the formation of a clathrin coat in insulin differ from others?

Answer 2

Clathrn coat only forms when a receptor has a ligand bound

Question 3

What are the general stages of RME?

Answer 3

Receptors cluster over clathrin, ligand binds causing conformational change, spontaneous constitutive invagination of membrane, forms coated vesicles, ATP dependent uncoating, vesicle fuses with endosome.

Question 4

What receptors are present for the uptake of cholesterol?

Answer 4

Cells that require cholesterol produce receptors for apoprotein B

Question 5

When LDL and its receptor reaches an endosome what happens?

Answer 5

The acidity reduces affinity of receptor for LDL TF it dissociates, receptor buds off in own vesicle and is recycled back to membrane. LDL buds off to lysosome. Cholesterol is de-esterified and released into the cell.

Question 6

What binds to the receptor in the uptake of FE3+?

Answer 6

Transferrin

Question 7

At what ph does transferrin bind to the receptor?

Answer 7

Neutral

Question 8

What forms transferrin?

Answer 8

Apotransferring and Fe3+

Question 9

In the uptake of cholesterol, what happens to the receptor and ligand?

Answer 9

Receptor: recycled. Ligand: degraded.

Question 10

In the uptake of Fe3+ what happens to the receptor and ligand overall?

Answer 10

Receptor: recycled. Ligand: degraded.

Question 11

When transferrin and the receptor reach an endosome what happens?

Answer 11

Acidity of the endosome lowers affinity of transferrin for Fe3+, so Fe3+ dissociates leaving behind apotransferrin bound to the receptor.

Question 12

What happens to the apotransferrin once Fe3+ has dissociated in RME?

Answer 12

Receptor with apotransferrin bound bud off in vesicle and are recycled to membrane. When the extracellular pH drops (more acidic) affinity of receptor for apotransferrin drops and so it dissociates.

Question 13

What happens in the RME of insulin that is different to others?

Answer 13

In the late endosome, the receptor and insulin remain bound and so both are delivered to the lysosome. Lysosomal enzymes TF degrade both receptor and insulin.

Question 14

How does the way the RME of insulin work lead to desensitisation of target cells to insulin?

Answer 14

Every time insulin binds, receptor complex is internalised and degraded. (More insulin, more degradation). Rate of synthesis cant keep up, TF overall loss of receptors.

Question 15

Is the formation of Clathrin spontaneous or need ATP?

Answer 15

Spontaneous

Question 16

What can result from mutations regarding receptors in RME?

Answer 16

Can lead to receptor deficiency (if mutation prevents expression of receptor), non-functioning receptor (TF ligand cant bind), normal receptor but there has been a deletion of the C terminus domain meaning receptor cant interact with the clathrin TF cant be internalised.