Unit 3 - Cell Signalling Flashcards
what is the difference between a protein kinase and phosphatase?
kinase - phosphorylates - switches proteins on - active form
phosphatase - dephosphorylates (removes a protein) - switches off - inactive form
what is the effect of protein kinase to the proteins?
conformational changes in proteins causes post-translational modifications in different parts of the protein
- phosphoserine/ phosphothreonine/ phosphotyrosine
what are the two main classes of kinases?
serine/ threonine kinases: - PKA, PKB, PKC - MAPK - cyclin dependent kinases tyrosine kinases: - growth factors - oncogenes
what is a protein kinase cascade?
receptor kinases is activated by hormone and becomes autophosphorylated and then series of phosphorylations which amplifies the amount of protein at each level
- e.g. MAPKKK - MAPKK - MAPK
what is the difference in calcium concentration in ECF and cytosol?
ECF = 1mM
cytosol = 100 nM
(thousandfold)
what causes release of calcium from endoplasmic reticulum?
neurotransmitter acts on voltage gated sodium channel
depolarisation causes sodium influx
triggers opening of voltage gated calcium channels on ER
OR
production of IP3 activates release of calcium
what protein does calcium bind to and what effect does this protein have?
calcium binds to calmodulin
calmodulin activates CAM kinase which triggers a protein cascade and targets different proteins such as:
- myosin light chain kinase = smooth muscle contraction
- nitrogen oxide synthase = release of nitrogen oxide
give five examples of 2nd messenger molecules
cAMP cGMP PIP3 DAG IP3
what is the effector of cAMP and describe what it activates
adenylate cyclase (catalyses conversion of ATP to cAMP)
cAMP activates PKA
(PKA inactivates myosin light chain kinase or activates glycogen phosphorylase)
what is the effector of cGMP and describe what it activates
guanylate cyclase (catalyses conversion of GTP to cGMP)
cGMP activates PKG
(PKG activates myosin phosphatase)
what is the effector of PIP3 and describe what it activates
PI3K (catalyses conversion of PIP2 to PIP3)
PIP3 activates PDK1 to activate PKB
(PKB activates mTOR leading to cascade of signalling for growth and proliferation)
what is the effector of DAG/ IP3 and describe what it activates
phosholipase C (catalyses hydrolysis of PIP2 to DAG/IP3) IP3 binds to calcium channels on ER to release more calcium DAG activates PKC (calcium also activates PKC) which activates PIP2 to produce more IP3 - amplify release of calcium
describe the structure of G proteins
7 transmembrane alpha helices with 3 subunits: alpha/ beta/ gamma
describe the mechanism of G proteins
ligand binds to GPCR - alpha subunit exchanges GDP fror GTP
- alpha subunit dissociates and regulates effector which relays signal by 2nd messenger molecules
how is GTP hydrolysed and what is the significance of this?
hydrolysed by GTPase back into GDP
rate of hydrolysis determines the length of time protein in active form
(can be modulated by RGS and GAP proteins)
name three classes of G proteins
Gas - activates adenylate cyclase
Gai - inhibits adenylate cyclase
Gaq - activates phospholipase C
describe the mechanism of enzyme- linked receptors e.g. RTK - receptor tyrosine kinases
agonist binds to domain on receptor
undergoes dimerisation reaction
phosphorylates each other
act as docking site for signal proteins
how is cGMP/cAMP/ PIP3 degraded?
cGMP/cAMP degraded by phosphodiesterase
PIP3 degraded by PTEN
how are GPCR regulated?
binding of arrestin blocks G protein binding
how does acetylcholine induce nitric oxide production?
Ach binds to G protein which uses class Gaq to activate phospholipase C - catalyses hydrolysis of PIP2 production of IP3 causes release of calcium activating calmodulin - stimulates NOS
what is the effect of nitrogen oxide?
activates guanylate cyclase which catalyses conversion of GTP to cGMP
cGMP activates PKG which activates myosin light chain phosphatase
- smooth muscle relaxation and vasoconstriction
how does insulin induced signalling promote glucose uptake?
insulin binds to RTK forms a docking site for IRS protein
IRS activates PI3K to convert PIP2 to PIP3
PIP3 activates PDK1 to PKB which stimulates more GLUT4 incorporated into membrane
how does glucagon promote glycogenolysis?
glucagon activates Gas - adenylate cyclase - PKA
PKA phosphorylates phosphorylase kinase which activates glycogen phosphorylase (glycogen - glucose 1P-glucose6P-glucose)
how does PKA promote gluconeogenesis?
phosphorylates PFK2 (substrate cycle) and activates FBPase2 which converts Fru 2,6 BP to Fru 6P fru 6P - glc 6P to glucose
