MCB 2050 Midterm Questions With Complete Solutions
What is the active G-protein able to bind to?
Downstream effector proteins
What is one of the most frequently activated enzymes in signal
transduction?
Adenylyl cyclase
What does adenylyl cyclase do?
Convert ATP to cAMP
What is the structure of GPCRs?
7 transmembrane alpha helices, with N terminus projecting out
and C terminus projecting in
What makes the ligand binding domain of a GPCR?
The combination of the exterior parts of the protein (links
between helices)
What is the G-protein structure?
Galpha = GTPase switch protein. Attached to GTP/GDP,
hydrophobic end keeps it anchored to membrane
Gbeta/gamma = rest of it, Ga dissociates from it when active.
Also bound to membrane
What is the mechanism of G-protein switches?
1. Ligand binds to inactive receptor, causing a conformation
change
,2. Active receptor binds Galpha (bound to Gbeta and gamma
3. Active receptor does GEF act - GDP leaves and GTP binds
4. Active Galpha dissociates
5. Galpha activates effector
6. Galpha does GTPase to go back to inactive, turning off
effector
What is the FRET technique?
Used to determine protein-protein interactions, one is tagges
with CFP (cyan) and one with YFP (yellow). When excited and
close, the light from cyan excites the yellow and yellow light is
emitted. When far, only cyan is emitted.
In graph: when light goes down, means Galpha dissociated, so
the thing added was a ligand to the receptor
What are the steps of the adenylyl cyclase pathway?
1. ligand binds receptor
2. receptor activates G protein
3. G protein activates adenylyl cyclase
4. Adenylyl cyclase makes cAMP
The same pathway on a diff receptor can inhibit adenylyl
cyclase
5. cAMP activates PKA by binding to it's inhibitor
6. inhibitor falls off, PKA goes into nucleus
7. PKA phosphorylates CREB
,8. Active CREB binds with CBP/p300 and together bind to CRE
regulatory element on promoter of many genes
9. Stimulates txn of target genes
What is the difference between tyrosine kinase receptor
pathways and Adenylyl cyclase pathway?
RTKs use phosphorylation, and not GDP-GTP switching. These
are different mechanisms
What are 4 different types of signal transduction pathways?
1. Receptor Kinases: kinase phosphorylate and activate txn
factor
2. Cytosolic kinases: receptor activates G-switch proteins
3. Protein subunit dissociation pathways: ligand makes
dissassembly of a complex, one of the components is a txn
factor
4. Protein cleavage pathways (irreversible signaling)
What are the steps of RTK activation?
1. Growth factor ligand activate RTKs on membrane
2. RTKs dimerize, bringing the activation loops in a different
formation: makes RTK more active
3. Autophosphorylation of RTKs
- starts with activation loop tyrosines
- then rest of tyrosines
What are the steps of the Ras-MAPK pathway?
1) Ligand binds RTKs: dimerize and autophosphorylate
2) SH2 in Grb2 recognizes the phosphorylated tyrosines and
, binds. SH3 of Grb2 recognizes prolines in Sos and bind
3) Binding of Grb2 to RTK and Sos couples the receptor to
inactive Ras (GDP)
4) Sos acts as GEF and activates Ras
5) active Ras-GTP detaches from Sos, but is bound to membrane
6) Active Ras-GTP binds to inactive MapKKK (MapKKK is
bound to 14-3-3, which inhibits it)
7) Ras does GTPase, phosphorylating MapKKK, releasing 14-3-
3
8) MapKKK phosphorylates MapKK
9) MapKK phosphorylates MapK
10) MapK activates p90^RSKinase
11) Both MapK and p90Rskinase move to nucleus
12) MapK phosphorylates TCF on promoter, p90rsk
phosphorylates SRF
13) 2 SRFs bind to promoter with TCF = mini enhancer,
stimulates transcription
What does PI-3 kinase do?
It makes the signaling complexes (membrane bound 2nd
messengers) that activate PKB:
IP2 : Phosphoinositol 3,4-biphosphate or 4,5-biphosphate
IP3: phosphoinositol 3,4,5-triphosphate
What is the PI-3 kinase pathway?
- RTK activate PI-3 kinase, which is bound to them with SH2
- PI-3 makes PI-3 phosphates IP2 and IP3
- IP2 and IP3 (membrane bound) binds to PH domain of PKB
(inactive PKB to partially active PKB)
What is the active G-protein able to bind to?
Downstream effector proteins
What is one of the most frequently activated enzymes in signal
transduction?
Adenylyl cyclase
What does adenylyl cyclase do?
Convert ATP to cAMP
What is the structure of GPCRs?
7 transmembrane alpha helices, with N terminus projecting out
and C terminus projecting in
What makes the ligand binding domain of a GPCR?
The combination of the exterior parts of the protein (links
between helices)
What is the G-protein structure?
Galpha = GTPase switch protein. Attached to GTP/GDP,
hydrophobic end keeps it anchored to membrane
Gbeta/gamma = rest of it, Ga dissociates from it when active.
Also bound to membrane
What is the mechanism of G-protein switches?
1. Ligand binds to inactive receptor, causing a conformation
change
,2. Active receptor binds Galpha (bound to Gbeta and gamma
3. Active receptor does GEF act - GDP leaves and GTP binds
4. Active Galpha dissociates
5. Galpha activates effector
6. Galpha does GTPase to go back to inactive, turning off
effector
What is the FRET technique?
Used to determine protein-protein interactions, one is tagges
with CFP (cyan) and one with YFP (yellow). When excited and
close, the light from cyan excites the yellow and yellow light is
emitted. When far, only cyan is emitted.
In graph: when light goes down, means Galpha dissociated, so
the thing added was a ligand to the receptor
What are the steps of the adenylyl cyclase pathway?
1. ligand binds receptor
2. receptor activates G protein
3. G protein activates adenylyl cyclase
4. Adenylyl cyclase makes cAMP
The same pathway on a diff receptor can inhibit adenylyl
cyclase
5. cAMP activates PKA by binding to it's inhibitor
6. inhibitor falls off, PKA goes into nucleus
7. PKA phosphorylates CREB
,8. Active CREB binds with CBP/p300 and together bind to CRE
regulatory element on promoter of many genes
9. Stimulates txn of target genes
What is the difference between tyrosine kinase receptor
pathways and Adenylyl cyclase pathway?
RTKs use phosphorylation, and not GDP-GTP switching. These
are different mechanisms
What are 4 different types of signal transduction pathways?
1. Receptor Kinases: kinase phosphorylate and activate txn
factor
2. Cytosolic kinases: receptor activates G-switch proteins
3. Protein subunit dissociation pathways: ligand makes
dissassembly of a complex, one of the components is a txn
factor
4. Protein cleavage pathways (irreversible signaling)
What are the steps of RTK activation?
1. Growth factor ligand activate RTKs on membrane
2. RTKs dimerize, bringing the activation loops in a different
formation: makes RTK more active
3. Autophosphorylation of RTKs
- starts with activation loop tyrosines
- then rest of tyrosines
What are the steps of the Ras-MAPK pathway?
1) Ligand binds RTKs: dimerize and autophosphorylate
2) SH2 in Grb2 recognizes the phosphorylated tyrosines and
, binds. SH3 of Grb2 recognizes prolines in Sos and bind
3) Binding of Grb2 to RTK and Sos couples the receptor to
inactive Ras (GDP)
4) Sos acts as GEF and activates Ras
5) active Ras-GTP detaches from Sos, but is bound to membrane
6) Active Ras-GTP binds to inactive MapKKK (MapKKK is
bound to 14-3-3, which inhibits it)
7) Ras does GTPase, phosphorylating MapKKK, releasing 14-3-
3
8) MapKKK phosphorylates MapKK
9) MapKK phosphorylates MapK
10) MapK activates p90^RSKinase
11) Both MapK and p90Rskinase move to nucleus
12) MapK phosphorylates TCF on promoter, p90rsk
phosphorylates SRF
13) 2 SRFs bind to promoter with TCF = mini enhancer,
stimulates transcription
What does PI-3 kinase do?
It makes the signaling complexes (membrane bound 2nd
messengers) that activate PKB:
IP2 : Phosphoinositol 3,4-biphosphate or 4,5-biphosphate
IP3: phosphoinositol 3,4,5-triphosphate
What is the PI-3 kinase pathway?
- RTK activate PI-3 kinase, which is bound to them with SH2
- PI-3 makes PI-3 phosphates IP2 and IP3
- IP2 and IP3 (membrane bound) binds to PH domain of PKB
(inactive PKB to partially active PKB)
