Effector Mechanisms in Intracellular Signalling -- 7.2

Question 1

At what part of teh cell does signal transduction tend to take place?

Answer 1

At the edge of the cell

Question 2

What does adenylyl cycles cause the conversion of?

What does this effector do?

Answer 2

ATP to cAMP
– uses ~1% of cells ATP concentration

cAMP causes the action of cAMP dependent protein kinase (PKA)
– binding of cAMP to regulatory subunits activates catalytic subunits which phosphorylate target proteins in the cell

Question 3

What does phospholipase C cause the conversion of?

Answer 3

PIP2 to IP3 and DAG

Question 4

What does phosphonositide 3-kinase cause the conversion of?

Answer 4

PIP2 to PIP3

Question 5

What does cGMP phosphodiesterase cause the conversion of?

Answer 5

Cyclic GMP to 5’GMP

Question 6

Which receptors have an effect on adenylyl cyclase?

Answer 6

Gs-coupled receptors
-- β-adrenoceptors
-- D1 dopamine receptors 
-- H2 histamine receptors
Gi coupled receptors
-- α2-adrenoceptors
-- D2 dopamine receptors 
-- μ-opioid receptors

Question 7

What receptors have an effect on phospholipase C?

Answer 7

Gq-coupled receptors

• • α1-adrenoceptors
• • M1 muscarinic receptors
• • H1 histamine receptors

Question 8

How are signals amplified?

Answer 8

The enzyme in the reactions causes a multiple product molecules, which causes the amplification

Question 9

Describe the action of phospholipase C

Answer 9

Catalyses the cleavage of PIP2 into IP3 and DAG

1. Agonist binds and causes a conformational change
2. GTP for GDP eachange takes place
3. Alpha-q GTP activates PLC
4. PLC cleaves PIP2 to IP3 and DAG

Question 10

What does IP3 cause?

Answer 10

Opens IP3 receptor

causes Ca2+ to flow into cytoplasm from SR/ER

Question 11

Describe positive ionotropy in the heart

Answer 11

Adrenaline in the blood and noradrenaline bind to B1 adrenoceptors in the ventricular walls –> releases cAMP –> activates PKA –> phosphorylates and activates VOCC –> increase [Ca] –> Ca induced Ca release

ALSO – alpha-s GTP directly interacts with VOCCs

Question 12

Describe arteriolar vasoconstriction

Answer 12

Noradrenaline binds to alpha1 adrenoceptors, stimulating phopholipase C

• • generates InsP3 (releases ER Ca2+) giving a contractile response
• • DAG activates protein kinase which phosphorylates target proteins to maintain the vasoconstriction

Question 13

The action of what hormone causes venoconstriction on which receptors?

Answer 13

noradrenaline acts on alpha1 adrenoceptors to cause venoconstriction

Question 14

The action of what hormone causes bronchoconstriction on which receptors?

Answer 14

Parasympathetic ACh acts on M3 muscarinic receptors

Question 15

Where else can smooth muscle be contracted?

Answer 15

GI tract and genitio-urinary smooth muscle

Question 16

Though which effector does smooth muscle contraction come about?

Answer 16

Gq phospholipase C to IP3 (Ca2+) and DAG (PKC)

– Increasing [CA] will increase contractility

Question 17

What regulates neurotransmitter release?

Answer 17

presynaptic G protein- coupled receptors are regulators in both the PNS and CNS

Question 18

How is neurotransmitter release regulated?

Answer 18

G-beta/gamma subunits inhibit specific types of VOCCs reducing Ca2+-influx which limits neurotransmitter release

Question 19

What receptors are involved in neurotransmitter release?

Answer 19

μ-opioid receptors