7: Cell Signalling And Transduction Flashcards
1
Q
Second messengers
A
Small non-protein molecules that relay a signal to the interior of the cell
- cAMP
- IP3
- DAG
- Ca2+
2
Q
Basic signalling pathways
A
- GPCRs
- activate G proteins which then kick off a cascade, involving second messengers (cAMP, IP3)
- Receptor kinases
- kinases
- when they bind a ligand their kinase activity is activated and they kick off a phosphorylation cascade
3
Q
GPCRs
A
- huge family of proteins
- 7 transmembrane domains (a helices)
- named because they activate heterotrimeric G proteins
- contain a variable region for ligands to bind on cytosolic side of membrane
- GTPases
- attached to GTP = ON
- Attached to GDP = OFF
4
Q
GTPases
A
- GTP = ACTIVE
- GDP = INACTIVE
- category 1
- monomeric and small
- ran, ARF, Sar 1
- category 2
- trimeric (3 subunits)
- a and g secure the G protein to the plasma membrane
- peripheral membrane proteins
- have small hydrophobic domain (can move around membrane)
5
Q
GPCR mechanism
A
- Resting state
- receptor not bound to ligand
- Ga is bound to GDP and associated with GBY
- Ligand binds receptor
- Ga releases GDP and acquires GTP (active)
- Ga and GBY subunits separate
- Ga leaves
- G protein subunits activate or inhibit target proteins
- imitates signal transduction events
- target protein = effector protein
- Ga subunit hydrolyzes its bound GTP to GDP
- now inactive
- target protein also inactivated
- Subunits recombine to form an inactive G protein
6
Q
Terminating GPCR response
A
- GRK (G protein receptor kinase) phosphorylates the GPCR
- Arresting binds the phosphorylated GPCR (now inactive)
- Arrestin recruits AP2
- AP2 recruits a clathrin coat
- GPCR is internalized by endocytosis
- GPCR in the endosome may have several fates
7
Q
Adenylyl Cyclase
A
- makes cAMP from ATP
- removes to phosphates and creates rung structure
- after ligand binds GPCR, G protein is activated, Ga subunit activates adenylyl cylase
- adenylyl cyclase makes cAMP
- GTP on Ga is hydrolyzed
- Ga dissociated from adenylyl cyclase so no more cAMP
8
Q
cAMP
A
- second messenger with many roles
- phosphodiesterase (PDE) will shut down signal
- convert cAMP to AMP
- main target is PKA (protein kinase A)
9
Q
PKA
A
- has 2 catalytic subunits (kinase activity) and 2 regulatory subunits (structural)
- regulatory subunits normally bind to catalytic subunits (inactive form)
- cAMP binds to the regulatory subunits of PKA and catalytic subunits are released
- catalytic subunits now available to phosphorylate/activate
10
Q
Fight or flight response
A
- mediated by cAMP/PKA
- PKA turns on transcription factors by going into nucleus and phosphorylation gets CREB
- also liberate glucose for use in muscles
- glycogen turned into glucose
11
Q
PLC
A
- phospholipase C
- makes lipid derived second messengers
- IP3 and DAG
- phosphotidylinositol with phosphates on inositol ring = PIP2
- PLC will cleave PIP2 into IP3 + DAG
- if a protein has a PH domain it will bind to PIP2
- PLC has a PH domain
- PLC will bind to PIP2 and cut it into IP3+DAG
- cuts between phosphate and glycerol
- IP3 made up of the phosphate+inositol
- DAG is the diagylglycerol tail
12
Q
PLC mechanism
A
- Ligand binds GPCR
- activates the G protein
- Ga stimulates PLC
- PLC cuts PIP2
- DAG remains in the membrane
- IP3 released into cytosol
13
Q
IP3 and DAG
A
- DAG stays in membrane and activates PKC
- IP3 goes into cytoplasm and binds IP3 receptors on ER to release Ca2+
14
Q
Calcium
A
- second messenger
- released by SER by IP3
- concentration of Calcium in SER is 10,000x higher than in cytoplasm
- once cell filled with calcium, ATP driven pumped will pump it back into SER
- need DAG and Ca2+ for PLC activation
15
Q
Calmodulin
A
- calcium binding protein
- contains 4 binding sites
- has very low affinity for calcium, so it is only activated when calcium concentration is VERY HIGH
- Calmodulin binds 4 calcium ions
- Calmodulin changes conformation, resulting in active complex
- The 2 globular hands of the complex wrap around a binding site on a target protein
