L14 - cell signalling

Question 1

what are 4 modes of cell communication

Answer 1

1. endocrine
2. paracrine
3. neuronal
4. contact dependant

Question 2

how many subunits does Gprotein have

what is it

Answer 2

3 (heterotrimeric) α β γ

Question 3

explain the mechanism of G-protein coupled receptors at the membrane

Answer 3

1. signal molecule binds GPCR
2. G protein (bound to GDP in inactive state) associates with receptor
3. GDP exchanged for GTP
4. causes G protein to dissociate from receptor
5. g protein dissociates into Gα-ATP and Gβγ
6. Gα-ATP diffuses along membrane until it reaches effector enzyme (adenylyl cyclase)
7. AC catalyses production of cAMP from ATP
8. eventually Gα hydrolyses ATP to ADP
9. Gαβγ complex reforms and signal ends

Question 4

define 2nd messenger

Answer 4

substance whose release is prompted by a substance binding receptor outside cell (hormone)

Question 5

how is cAMP produced

Answer 5

adenylyl cyclase catalyses reaction of ATP to cAMP

Question 6

describe structure of cAMP dependant protein kinase A

Answer 6

heterodimeric (2 subunits)
one regulatory subunit
one catalytic subunit
regulatory stops catalytic from working

Question 7

how does cAMP activate protein kinase A (signalling pathway)

Answer 7

1. cAMP binds to R subunit and they both diffuse away from the C
2. C subunit activated and can then phosphorylate other target proteins using ATP-ADP energy

Question 8

explain the activation of protein kinase C

Answer 8

1. target binds to GPCR on outside membrane
2. G protein Gαβγ (bound to ADP) associates with GPCR
3. ADP transferred to ATP
4. causes Gαβγ to dissociate from GPCR and Gα-ATP to dissociate from Gβγ
5. Gα-ATP diffuses along membrane finds and activates phospholipase C
6. phospholipase C hydrolyses inositol phospholipid releasing inositol 1,4,5 triphosphate (IP3) and diacylglycerol
   - —> potent 2nd messengers
7. IP3 causes Ca2+ release from channels
8. diacylglycerol diffuses along membrane until in contact with PKC and Ca2+ - PKC can then be activated

Question 9

what role does phospholipase C play in the activation of protein kinase C
(cell signalling pathway)

Answer 9

hydrolyses inositol phospholipid releasing inositol 1,4,5 triphosphate (IP3) and diacylglycerol
which are potent 2nd messengers

Question 10

what role does IP3 play in the activation of protein kinase C
(cell signalling pathway)

Answer 10

binds to Ca2+ channels in ER opening them and causing Ca2+ release

Question 11

what role does diacylglycerol play in the activation of protein kinase C
(cell signalling pathway)

Answer 11

diffuses along the membrane until it reaches protein kinase C
which it activates together with Ca2+

Question 12

role of Ca2+ in the activation of protein kinase C

cell signalling pathway

Answer 12

activates protein kinase C together with diacylglycerol at the membrane

Question 13

what does protein kinase C do after acivation

Answer 13

phosphorylate other proteins

Question 14

what are some other examples of signalling pathways

Answer 14

ACh

adrenaline

Question 15

what is a function of activated protein kinase A

Answer 15

activates glycogen synthase inhibitor (by phosphorylating)

decreases glycogen synthesis

Question 16

what 5 processes occur due to cell signalling

Answer 16

1. division
2. cell growth
3. differentiation
4. movement
5. cell death

Question 17

what amino acids can protein kinase A phosphorylate

Answer 17

serine

threonine

Question 18

characteristics of Gq linked GPCR

Answer 18

activates phospholipase C (2nd messenger) and eventually protein kinase C

Question 19

characteristics of Gs linked GPCR

Answer 19

activates cAMP (2nd messenger)

Question 20

example of a GPCR

Answer 20

B-adrenergic receptors binding adrenaline