Lecture 13: Intracellular Signalling Pathways & Regulation Of Calcium

Question 1

What are the three fundamental components of a signalling cascade?

Answer 1

Receptor
G-protein
Effector molecule can be enzyme or ion channel

Question 2

What does heterotrimeric proteins mean?

Answer 2

G-proteins are made up of 3 distinct subunits: alpha, beta and gamma

Question 3

What are the 2 regions of GPCR that ligands can bind?

Answer 3

1. Between transmembrane domains

2. N-terminal region

Question 4

What happens when ligands bind?

Answer 4

Change conformation of GPCR

Question 5

What is a G protein?

Answer 5

Guanine nucleotide binding protein

Question 6

What does G protein do?

Answer 6

G proteins contain GTPase which cleaves off 3rd phosphate from GTP to make GDP

Question 7

How does the GPCR-G protein interaction activate the G protein?

Answer 7

GTP exchange for GDP on the G protein alpha subunit

Question 8

What happens when G protein is activated?

Answer 8

alpha-beta gamma complex dissociates into alpha-GTP and free betagamma subunits and each can then interact with effector proteins

Question 9

How does G protein signalling terminate?

Answer 9

Alpha GTP and/or Beta gamma interaction with effectors last until the alpha subunit GTPase activity hydrolyses GTP back to GDP. alpha-GDP and beta gamma subunits then reform an inactive heterotrimeric complex

Question 10

What are 3 most studied G protein types?

Answer 10

G-alpha I, S and Q

Question 11

What does G alpha S do?

Answer 11

Stimulate adenylyl cyclase

Question 12

What does G alpha I do?

Answer 12

Inhibits adenylyl cyclase

Question 13

What does G alpha Q do?

Answer 13

Stimulates phospholipase C

Question 14

What are 2 toxins that can interfere with G protein function?

Answer 14

Cholera toxin and pertussis toxin

Question 15

How does pertussis toxin (PTx) interfere with G protein function?

Answer 15

It uncoupled GI-preferring GOCRsa from mediating signal transduction events by stopping GTP GDP exchange

Question 16

What does PTx pertussis toxin cause?

Answer 16

Pertussis (whooping cough)

Question 17

How does cholera toxin interfere with G protein function?

Answer 17

Prevents termination of signalling by Gs preferring GPCRs leading to long-lasting activation of downstream pathways - cannot inactivate

Question 18

What does cholera toxin cause?

Answer 18

Cholera

Question 19

How does G protein act as a transducer on/off switch with a timer?

Answer 19

When ligand binds and GDP/GTP exchange occurs, it switches it on, the length of the timer is equivalent to the length of time taken for GTP hydrolysis on the G subunit,

Question 20

What are the three ways that. A2+ homeostasis is maintained in the whole body?

Answer 20

1. Intestinal Ca2+ uptake
2. Ca2+ reabsorption in kidneys
3. Bone calcium regulation

Question 21

What are 3 examples of what intracellular [Ca2+] is responsible for?

Answer 21

Muscle contraction, neurotransmission and cell death

Question 22

What are 3 ways to set up and maintain Ca2+ concentration gradients?

Answer 22

• relative impermeability of plasma membrane to Ca2+
• pumps and transporters that move Ca2+ out of the cytoplasm
• Ca2+ buffer proteins that bind to Ca2+

Question 23

What are 2 ATP-dependent mechanisms to control Ca2+ concentration gradient?

Answer 23

PMCA and SERCA

Question 24

What is the transporter that regulates [Ca2+]?

Answer 24

Na+ Ca2+ exchanger

Question 25

What are 2 mechanisms that increases [Ca2+] by allowing Ca2+ to move across plasma membrane into the cell?

Answer 25

Ligand-gated ion channels and voltage-operated Ca2+ channels

Question 26

What are 2 ways that can increase [Ca2+] by moving Ca2+ out of the ER/SR?

Answer 26

IP3R and CICR ryanodine receptors

Question 27

What happens when agonist binds to a receptor and adenylyl cyclase is stimulated?

Answer 27

Adenylyl cyclase enzyme acts to hydrolyse cellular ATP to generate cyclic AMP

Question 28

What does cyclic AMP do?

Answer 28

Binds to regulatory subunits of protein kinase A and cause release of catalytic subunits which phosphorylation target proteins in the cell

Question 29

What does protein kinase A do?

Answer 29

PKA phosphorylates a variety of other proteins within the cell to increase or decrease their levels of activity

Question 30

What are 3 examples of receptors that causes stimulation of adenylyl cyclase?

Answer 30

GI coupled receptors

Beta-adrenoceptors
D1 dopamine receptors
H2 histamine receptors

Question 31

What happens when agonist binds to GPCR and inhibits adenylyl cyclase?

Answer 31

Cyclic AMP not produced, PKA not activated

Question 32

What are 3 examples of receptors that causes inhibition of adenylyl cyclase?

Answer 32

Gs coupled receptors

Alpha 2 adrenoceptor
D2 dopamine receptor
Opioid receptor

Question 33

What does phospholipase C do?

Answer 33

Catalyzes cleavage of membrane phospholipid PIP2 into 2 secondary messengers - IP3 and DAG

Question 34

What are 3 examples of receptors that regulate phospholipase C?

Answer 34

Gq coupled receptors

Alpha 1 adrenoceptors
M1 muscarinic receptors
H1 histamine receptors

Question 35

What does IP3 do?

Answer 35

Bind to IP3 receptors that control movement of Ca2+ from endoplasmic reticulum into cell cytoplasm

Question 36

What does DAG do?

Answer 36

Interact with protein kinase C and activates protein kinase C to phosphorylation other things

Question 37

What is signal amplification?

Answer 37

Relatively small changes in extracellular signals can cause physiologically significant changes in cellular behavior

Question 38

How does signalling pathway affect inotropy in the heart?

Answer 38

Adrenaline and noradrenaline can interact with ventricular beta1-adrenoceptors to increase force of contraction

Question 39

How do signaling pathways affect smooth muscle contraction?

Answer 39

Noradrenaline interact with vascular smooth muscle alpha1 receptors to cause vasoconstrictiom

Acetylcholine can interact with bronchiolar smooth muscle M3 muscarinic receptors to cause bronchoconstriction