Week 1

Question 1

GPCR

Answer 1

G protein Coupled receptors

-transmission of signals from ligand (ex. NT, hormone etc)

Question 2

G protein

Answer 2

1) Subunits:
- Alpha
- Beta
- Gamma
2) Can act as GTPases (alpha subunit)
- converts GTP->GDP

Question 3

G-S type signaling pathway

Answer 3

1) Stimulatory
2) Ligand= Epinephrine (1st messenger)
3) 2nd Messenger= cAMP
4) Steps
- Epi released from adrenal medulla binds to B-1 receptor
- Conformational change of the receptor on the 3rd intracellular loop
- Causes conformational change of G protein
- Alpha subunit is released attached to GDP (inactive form) and Beta/Gamma released within cell
- GDP attached to alpha subunit is phosphorylated to GTP (active form of alpha subunit)
- alpha subunit activates adenylyl Cyclase-> ATP-cAMP
- cAMP binds to PKA
- PKA phosphorylates other proteins changing their function
5) Increases HR

Question 4

How do you reverse the effects of G-S type signaling pathway

Answer 4

1) No more epinephrine
2) GTPase of the G-Protein cleaves GTP->GDP
- alpha subunit reattached to Beta/Gamma subunits
- goes and find the receptors
3) still have a lot of cAMP conc./High cAMP conc
- Phosphodiesterases-PDEs converts cAMP to AMP
- PKA lowers in activity
4) Phosphatase dephosphorylates whatever was phosphorylated by PKA

Question 5

G-I type signaling pathway

Answer 5

1) Inhibitory
2) Ligand=Ach
3) Decreases Heart Rate (opposite of stimulatory G pathway)
4) Steps
- Ach binds to M2 receptor of heart causing a conformation change
- and conformational change of G protein
- alpha subunit with GDP converted to GTP
* *Does not go to ADENYLYL CYCLASE (AC) instead PLC on PM
* breaksdown PIP2 into DAG and IP3
* IP3 binds to IP3 receptor on smooth ER, stimulating it
- now acts as an ion channel, Ca2+ goes to cytosol (high concentration in smooth ER)
- Ca2+ stimulates PKC which phosphorylates other proteins

Question 6

How do you reverse the effects of G-I type signaling pathway

Answer 6

1) Ligand goes away (Ach(
2) G protein alpha subunit acts as an GTPase converts GTP to GDP
3) GDP binds to B/Y subunit
- doesn’t change IP3 and DAG
4) IP3 and DAG resynthesizes to PIP2
5) Ca2+ goes back into SER via SERCA (smooth ER calcium ATPase-uses ATP)
- primary activity transport