G-alpha subunits

4 G-alpha-type subunits

Gs

Gi

Gq

G12

Members of Gs

Gs

Golf

Members of Gi

Gi, Go, Gz

Gt, Ggust

Members of Gq

Gq, G11, G14, G15, G16

G12

G12 and G13

Gs function

Simulates activity of adenylate cyclase —> increased cAMP production —> PKA activationG

Gs also activates

calcium channels

Golf function

Stimulates activity of adenylate cyclase in olfactory sensory neurons

Gi, Go, Gz function

Inhibit adenylate cyclase —> inhibit cAMP productionT

The beta,gamma subunits associated with Gi activates

potassium channels

The beta,gamma subunits associated with Go activates

potassium channel and inactivates calcium channel

Gt, Ggust

Activates cyclic GMP phosphodiesterase —> increased hydrolysis of cyclic nucelotides

Gt is the alpha subunit of

transducing involved in night vision (rod photoreceptors)G

Ggust is the alpha subunit of

gustducin involved in gustatory system

Gq, G11, G14-G16 function

Activates phospholipase C-beta —> increased production of IP3 and DAG

G12 and G13 function

Activates Rho family of monomeric G-proteins and regulate the actin cytoskeleton

GPCRs are

7 pass transmembrane receptors

GCPRs activate

G proteins

(guanine nucleotide binding proteins)

G proteins made up of 3 subunits

alpha

beta

gamma

alpha and gamma subunits of G proteins

anchored to cell membrane and keep G protein right next to receptor

G proteins bind to ___ when they’re inactive

GDP

(guanosine diphosphate)

When ligand binds to GCPR

changes shape —> allows G protein to release GDP and bind GTP instead, activated protein

When alpha subunit bound to GTP…

it separates from beta and gamma subunits so it can interact with other proteins

To act on other proteins, alpha subunit turns

GTP —> GDP which causes 3 subunits to come together and G protein turned off

Gq activates

phospholipase C found in cell membrane —> cleaves phosphatidylinositol 4,5-bisphosphate into IP3 and DAG

IP3

soluble, diffuses freely through cytoplasm and into ER where it opens up calcium channels —> can lead to depolarization

DAG

attached to cell membrane and attaches to Kinase C which requires calcium to activate

Protein kinase C activates proteins by

adding phosphoryl groups to them

Only when there is increased calcium concentration

Gs stimulates

adenylate cyclase

Active adenylate cyclase

takes ATP, removes 2 phosphate molecules and transforms ATP into cAMP

cAMP moves throughout cytoplasm, binds to protein kinase A

Protein Kinase A has

2 parts = regulatory subunit and catalytic subunit

cAMP binds the ___ of protein kinase A

regulatory subunit —> causes it to dissociate from catalytic subunit

Once dissociated from regulatory subunit, catalytic subunit can

go target proteins to trigger cellular response

Gi also bound to

adneylate cyclase, but it inhibits it causing negative feedback on G proteinsG

Gi important to help

inactivate cells