Membranes and Receptors (ESA 2)

Question 1

Haemolytic Anaemias

Answer 1

hereditary spherocytosis: spectrin depleted by 40-50%, RBCs become spherical, less resistant to lysis and the RBCs are broken down by the spleen Hereditary elliptocytosis: defect in spectrin, cannot form heterotetramers, forms fragile elliptoid cells

Question 2

two toxins that have an effect on the G-protein cycle

Answer 2

cholera

pertussus

Question 3

effects of cholera and pertussus toxins on the g-protein cycle

Answer 3

cholera: elimates GTPase activity of Galp_s -> Galp_s becomes irreversibly activated
pertussus: interferes w/ GDP/GTP exchange on Galp_i -> irreversibly inactivated

Question 4

give 3 disease caused by mutations to GPCRs

Answer 4

genetic changes -> gain/loss of function

retinitis pigmentosa- loss of function to rhodopsin

nephrogenic diabetes insipidus- loss of function to V₂ vasopressin receptor

familial male precocious puberty- gain of function (ie receptor active w/o ligand) to Luteinising hormone (LH) receptor

Question 5

retinitis pigmentosa

Answer 5

loss of function to rhodopsin

Question 6

nephrogenic diab insip

Answer 6

loss of function to V₂ vasopressin receptor

Question 7

familial male precocious puberty

Answer 7

gain of function (ie receptor active w/o ligand) to LH receptor

Question 8

mutations affecting LDL receptor in hypercholesterolaemia

Answer 8

1 non functioning receptor: mutation to binding site of LDL receptor -> prevent binding and uptake of LDL

2 receptor binding is normal: deletion of C terminal cytoplasmic domain -> prevents interaction between receptor and clathrin coat -> LDL receptors will be distributed all over the cell, not just 2%

3 receptor deficiency: mutation -> prevents expression of LDL receptor