Receptors 1

Question 1

Outline the concept and nature of receptor signalling.

Answer 1

Transfer a signal from the outside of a cell to the interior. may be by opening or closing membrane ion channels, or stimulating enzyme activity causing synthesis of a product or 2nd messenger

Question 2

Describe the structure of G-protein coupled receptors.

Answer 2

7 transmembrane alpha-helices, G protein has 3 subunits (a,B, y).

Question 3

Outline the signalling cascades in GPCR signalling.

Answer 3

Agonist occupies receptor couples with alpha subunit, GTP replaces GDP, alpha subunit and GTP travel to interact with effector enzyme, hydrolyzing GTP, alpha subunit reunites with By complex

Question 4

Explain how G-proteins regulate effector enzymes

Answer 4

G proteins activate or inhibit effector proteins depending on the subunit family. G(as) activates AC, G(ai) inhibits AC, By subunits activate or inhibit AC depending on AC isoform

Question 4

Explain how G-proteins regulate effector enzymes

Answer 4

G proteins activate or inhibit effector proteins depending on the subunit family. G(as) activates AC, G(ai) inhibits AC, By subunits activate or inhibit AC depending on AC isoform

Question 5

Adenylate cyclase mechanism of action.

Answer 5

Adenylate cyclase- activated by B-adrenergic receptors, inhibited by a2 adrenergic receptors, activated by G(as), II, IV, VII activated by By, I and VIII inhibited by By. G(as) stimulates AC to produce cAMP, which activates protein kinases, which activate many ion channels and metabolic pathways, cAMP is then broken down by phosphodiesterase. G(ai) inhibits AC.

Question 6

Phospholipase C-B mechanism of action.

Answer 6

Regulated by G proteins, hydrolyses phosphoinositide from the membrane, produces DAG and inositol triphosphate (IP3) second messengers. IP3 is water soluble, binds IP3 receptor in ER, causing release of Ca++, signal terminated by removal of terminal phosphate. Ca++ causes smooth muscle contraction, increases force of cardiac muscle contraction, transmitter release from neurons, hormone release. DAG is lipid soluble, activates protein kinase C in the membrane, which causes hormone release, contraction and relaxation of smooth muscle, Ca++ and K+ ion transport.

Question 7

Phospholipase C-B mechanism of action.

Answer 7

Regulated by G proteins, hydrolyses phosphoinositide from the membrane, produces DAG and inositol triphosphate (IP3) second messengers. IP3 is water soluble, binds IP3 receptor in ER, causing release of Ca++, signal terminated by removal of terminal phosphate. Ca++ causes smooth muscle contraction, increases force of cardiac muscle contraction, transmitter release from neurons, hormone release. DAG is lipid soluble, activates protein kinase C in the membrane, which causes hormone release, contraction and relaxation of smooth muscle, Ca++ and K+ ion transport.