WHAT A LADD

Question 1

(1) Structure of GPCRs

Answer 1

• 7 transmembrane domains
• Exoplasmic N-terminal binds ligand
• Cytoplasmic loop 3 interacts with G protein
• Cytoplasmic C-terminal tail involved in regulating GPCR

Question 2

(1) 3 main mammalian GPCR subfamilies

Answer 2

A: Rhodopsin-like group (most of GPCRs)
B: Secretin receptor family
C: Venus fly trap: Metabotropic gluatmate and GABAa receptor family

Question 3

(1) VAS IS DAS Orphan receptors

Answer 3

GPCRs that are identified which family they are in by homology cloning but unknown activating ligand

Question 4

(1) What are RGS

Answer 4

Regulators of G protein signalling

Question 5

(1) G proteins and 2nd messenger

Answer 5

Gs = mediated by alpha (adenylyl cyclase + Ca2+ channels)
Gi = alpha = inhibits adenylyl cyclase
Gq = alpha = activates phospholipase C-B

Question 6

(1) G-protein cycle thingy

Answer 6

1) Resting (GDP-bound) state
2) Ligand binding and nucleotide exchange in Ga (GDP to GTP)

3) Active (GTP-bound state)
Ga dissociates and binds effector
GB and Gy bind other effector (Internal signalling occurs

4) GTPase activates
RGS binds Ga (GTP to GDP)

5) Ligand dissocaition, G-protein timer formation

Question 7

(1) Common experimental tools used to study GPCRs

Answer 7

1) Cholera toxin
-Causes ADP ribsoylation of Gas
-Prevents GTP hydrolysis
-ALWAYS activating adenylate cyclase
-Lots of cAMP
DEATH

2) Pertussis Toxin (PTX)
- Causes ADP ribosylation of Gai
- Prevents release of GDP. INACTIVE
- Prevents inhibition of adenylate cyclase
- Same as cholera

Question 8

(1) RGS proteins function

Answer 8

Negative regulators of G protein signalling

-Enhance Ga proteins intrinsic GTPase activity

Question 9

(1) Regulation of GPCR function

Answer 9

1) De/resensitisation: Decrease in responsivness during continous drug application (right-shift in drug dose response curve)
- Long term desense: Changes in G protein levels, mRNA expression
- Rapid desense: Receptor phos, arrestin binding, receptor internalisation

Question 10

(1) 2 types of densensitisation

Answer 10

Heterologous desense: 2nd messneger kinase (PKA/PKC) = Then arrestin bindig

Homologous desense: G-protein coupled receptor kinase (GRK)

B-arresting binding to phos GPCR is required to decrease GTPase activity prior to densense

Question 11

(1) Arrestin mechanisms

Answer 11

• Promotes uncoupling of G protein
• Desense by binding to clathrin and calthrin adaptor protein AP2
• Promotes G-protein independent signalling

Question 12

(1) GPCR heterodimers

Answer 12

Family C GPCRs
ALSO Rhodopsin homodimers
(e.g. Vasopressin and OT Rs)

Question 13

(1) VAS IS DAS Orthosteric site

Answer 13

The site where agonists and antagonists bind to on a GPCRs
PAM: Positive allosteric modulator
NAM: Negative allosteric modulator

Question 14

(1) VAS IS DAS Signal bias

Answer 14

GPCRs have a preference and higher affinity for certain ligands over other and produce a greater response to them.

Question 15

(2) Diabetes

Answer 15

A metabolic disorder of multiple aetiology characterised by chronic hyperglyceamia with disturbances of carbohydrate, fat and protein metabolism resulting from defects in insulin secretion or action or both.

Question 16

(2) Type 1 diabetes treatments

Answer 16

1) Islet transplantation
2) Insulin
3) Diet, exercise
4) Lifestyle

Question 17

(2) Type 2 diabetes treatments

Answer 17

1) Lifestyle
2) Diet, exercise (decrease fat content as its assocaited with increased insulin sensitivity)
3) Oral monotherapy
4) Oral combination therapy
5) Insulin (with or without oral agent)

Question 18

(2) Supplemtments in type 2 diabetes

Answer 18

1) statins: Stop liver cholesterol
2) Fibrates: Less effective lowering LDL, improve HDL and triglyceride levels). Improve insulin resistance
3) Resins: Bind cholesterol
4) Orlistat: Inhibits pancreatic lipase, prevent triglyceride digestion from gut. Decreases fat absorption

Question 19

(3) GLP-1 effects in humans

Answer 19

1) B cell: Enhances glucose-dependent insulin secretion
2) A cell: Suppresses postprandial glucagon secretion
3) Liver: Reduces hepatic glucose output
4) Stomach: Slows rate of gastric emptying
5) Brain: Promotes satiety and reduces appetite

Question 20

(3) Treatments of Hyperglycaemia

Answer 20

1) Increased carbohydrate intake: Alpha glucosidase inhibitors
2) Decreased Insulin secretion: Sulphonylureas
3) Decreased pheripheral glucose uptake (insulin resistance): Metformin / Thiazolidinediones
4) Increased hepatic glucose output: Metformin (Glucophage)

Question 21

(3) How Thiazolidinediones work

Answer 21

1) Bind PPARy nuclear receptor
2) PPARy complexes with Retinoid X receptor (RXR)
3) Enhances insulin selective genes (e.g. GLUT-4 and Lipoprotein lipase)
RESULT: Increased glucose uptake and lipogenesis and decreased circulating fatty acids

Question 22

(3) How metformin works

Answer 22

-Its a biguanide
-Unchanged by kidneys
ACTION
1) Reduces hepatic gluconeogenesis
2) Decreased absorption of glucose from GI tract
3) Increased insulin sensitvity by increasing peripheral glucose uptake and utilisation

Question 23

(3) How Alpha-glucosidase inhibitors work

Answer 23

Act as competitive inhibtors of enzymes required to digest carbohydrates.

• Used to decrease current blood glucose levels
  (e. g. Acarbose)