ion channels and g proteins

Question 1

3 steps of a signal transduction?

Answer 1

1) extracellular signal molecule activates membrane receptor
2) intracellular molecules transduced via a pathway
3) cell response activated

Question 2

what is an extracellular signal? (Give examples)

Answer 2

A first messenger
- amines (adrenaline)
-steroid hormones
- proteins and peptides

Question 3

what is an intracellular signal?

Answer 3

a second messenger molecule

Question 4

what act as transducers between systems?

Answer 4

membrane proteins

Question 5

4 classes of receptors?

Answer 5

ligand-gated ion channels
g-protein coupled receptors
enzyme-linked receptors
nuclear hormone receptors

Question 6

what are ionotropic receptors?

Answer 6

ligand gated ion channels that form an ion pore

Question 7

example of an ionotropic receptor

Answer 7

nicotinic acetylcholine receptor
Gaba A receptor

Question 8

Stages of nicotinic Ach receptor?

Answer 8

1) binding of Ach opens channel for Na+
2) binding of nicotine
3) electrical event triggers response
4) calcium released
5) muscle contraction

Question 9

What does Gaba A receptor inhibit?

Answer 9

inhibitor of neurotransmitters in CNS

Question 10

What drug class activates Gaba A?

Answer 10

benzodiazepines

Question 11

what are Gaba A receptors selective to?

Answer 11

chlorine ions

Question 12

what are muscarinic receptors?(example)

Answer 12

type of Ach g protein coupled receptor

Question 13

Examples of muscarinic receptors?

Answer 13

muscarinic ach receptor
Gaba B receptor- activated K+ channels

Question 14

How many domains do GPCR have?

Answer 14

7 transmembrane domains

Question 15

what are the 3 polypeptide chains of a g protein?

Answer 15

alpha, beta, gamma subunits

Question 16

what does the alpha subunit bind to?

Answer 16

GTP/GDP

Question 17

conditions of alpha-GDP?

Answer 17

resting condition - inactive g protein
high affinity to beta-gamma subunit

Question 18

affinity of alpha-GTP?

Answer 18

low affinity to beta-gamma subunit

Question 19

what does alpha subunit hydrolyse?

Answer 19

GTP to GDP

Question 20

structure of PKA?

Answer 20

2 catalytic 2 regulatory polypeptides

Question 21

what activates PKA?

Answer 21

binding of cAMP to R subunits

Question 22

what happens when C + R subunits are bound?

Answer 22

R supresses activity of C so PKA is inactive

Question 23

what happens when cAMP binds?

Answer 23

subunits dissociate
phosphorylation of other proteins allowed

Question 24

what responses rely on cAMP/PKA pathway?

Answer 24

• kidney collecting duct
• vascular smooth muscle and cardiac muscle
• pancreas release of glucose

Question 25

what hydrolyses cAMP?

Answer 25

phosphodiesterase (PDE)

Question 26

what happens when cAMP unbinds?

Answer 26

increases R affinity to C protein reassembles becomes inactive PKA

Question 27

what inhibits PDEs?

Answer 27

caffeine so cell response is prolonged PKA active for longer

Question 28

what does desensitization of a receptor do?

Answer 28

feedback mechanism to reduce signal transduction reduced cell response despite a sustained stimulus

Question 29

Different alpha subunits of g protein?

Answer 29

alpha s alpha i alpha q

Question 30

what does alpha s subunit do when activated?

Answer 30

simulates adenyl cyclase (AC) uses ATP to produce cAMP cAMP activates PKA phosphorylation of target protein

Question 31

what does alpha i subunit do?

Answer 31

inhibits AC decreases cAMP inactivates PKA

Question 32

Receptor that couples to Gs?

Answer 32

beta2-adrenoreceptors - vasodilation decrease BP vasopressin receptor

Question 33

Examples of receptor that couples to Gi?

Answer 33

alpha2 adrenoreceptors A1/3 adenosine receptors M2 muscarinic receptor

Question 34

Another class of g proteins?

Answer 34

Gq proteins with alpha q11 subunit

Question 35

what do Gq proteins do?

Answer 35

allow activation of phospholipase C (PLC)

Question 36

what does PLC do when stimulated by Gq protein?

Answer 36

cleaves PIP2 into IP3 and DAG

Question 37

what is IP3 and what does it do?

Answer 37

water-soluble part - hydrophilic travels through cytosol to stimulate calcium release from ER promotes cell response

Question 38

what does DAG do?

Answer 38

remains in membrane recruits protein kinase C (PKC)

Question 39

What are IP3, Calcium and DAG examples of?

Answer 39

second messengers

Question 40

what are calcium mediated responses?

Answer 40

mediated by Ca2+ binding proteins

Question 41

example of Ca2+ binding protein?

Answer 41

calmodullin CaM

Question 42

what does CaM do?

Answer 42

binds 4 Ca2+ ions complex activates PDE and CaM kinases (CaMKs)

Question 43

what do CaMKs do?

Answer 43

phosphorylate serine and threonine residues on proteins

Question 44

example of Gq protein receptor?

Answer 44

alpha 1 adrenoreceptor for vascular smooth muscle contraction Vasoconstriction increase BP

Question 45

Effects of DAG?

Answer 45

presence increases activity of Ca2+ dependent protein kinase phosphorylates PKC mediates desensitization