kowluru signal transduction

summarize homeostasis of blood glucose

1. low blood glucose-> pancreas alpha cells-> glucagon to liver-> glucose released

2. high blood glucose-> pancreas beta cells-> insulin to fat cells-> glucose taken in

islets of langerhans

areas of pancreatic cells that produce insulin and glucagon

a hormone stain of the islets of langerhans would have what colors? what do they represent?

green= beta cells-> insulin (60%= majority)

blue= alpha cells-> glucagon

pink= delta cells-> somatostatin

which cells of the pancreas form the majority of the islets of langerhans and what do they secrete

beta cells (60%)= insulin

summarize how insulin is released from beta cells

1. glucose lands on GLUT2= enters beta cell

2. metabolism

3. increased ATP/ADP ratio [AND GPCR activation-> Ip3-> calcium]

4. ATP causes K channel to close (K cannot leave)

5. membrane depolarization (more +)

6. Voltage dependent calcium channel opens (VDCC)

7. Ca2+ rushes in

8. increased Ca promotes insulin granule exocytosis

insulin is stored as ______ in ________ cells

granules; beta

what prevents movement of insulin granules to membrane under basal conditions? what stops these barriers?

cytoskeleton (ex: F-actin); glucose stimulus disrupts these barriers

3 major classes of G proteins

1. Trimeric= alpha, beta, gamma

2. Monomeric= single subunit; cytoskeletal reorganization

3. Tau= less studied, protein biosynthesis

t/f: all G proteins bind to GTP

true

GTP-bound form is ________

GDP-bound form is _________

gtp= active

gdp= inactive

inhibitory vs stimulatory G protein on cAMP

inhibitory decreases cAMP

stimulatory increases cAMP via adenylyl cyclase

t/f: under basal conditions, the heterotrimeric G protein stays as a complex, with the alpha subunit only dissociating upon activation

true; alpha dissociates when bound to GTP

the alpha subunit is active when it is bound to

GTP

which enzymes hydrolyzes GTP back to GDP

GTPase

t/f: both alpha and beta/gamma can activate effectors

true

small molecular mass G proteins role

- single subunits (20-25kDa)

- several classes that have many functions : cytoskeletal remodeling, vesicle fusion, docking

ex: Ras, Rho, Rac1

small G protein activation and deactivation

Gprotein + GDI (GDP dissociation inhibitor) = INACTIVE/GDP

->GEF (guanine nucleotide exchange factors): makes G-protein ACTIVE/GTP

->GAP= GTPase-activating protein= deactivates back to G + GDI

G-protein + GDI=

GEF=

GAP=

involved in small G protein activation/deactivation

GDI= GDP dissociation inhibitor= INACTIVE

GEF= guanine nucleotide exchange factors (MAKES ACTIVE)

GAP= GTPase activating protein (MAKES INACTIVE)

t/f: activation of small G proteins follows the same steps as the trimeric G proteins

false. small G protein involves GEFs, GAP, GDI

t/f: heterotrimeric G proteins are not anchored to the membrane and are allowed to float through the cytoplasm

false. they are anchored to the membrane via lipids

which post-translational modification steps assist in G protein lipid anchoring

alpha subunit= myristylation (N-terminus) and palmitoylation (cysteine)

gamma subunit= prenylation (C-terminus)

*note beta is attached to gamma which is attached to membrane

t/f: G protein lipid anchoring is a post-translational step

true

effects of lipidation of G-proteins (lipid anchoring)

1. increase hydrophobicity= translocation to membrane

2. increase interactions btwn proteins and receptors

3. increase association btwn subunits (alpha, beta, and gamma)

phospholipase C

enzymes that hydrolyzes phospholipids on the membrane; activated by GTP-alpha

cleaves PIP2 into DAG and IP3

PIP2 is a phospholipid cleaved by __________ into ____________

phospholipase C: DAG and IP3

DAG

diacylglycerol

stays in membrane (hydrophobic); activates protein kinase C

IP3

inositol triphosphate

hydrophilic; promotes calcium release

t/f: DAG is a hydrophilic molecule that forms upon PIP2 cleavage and leads to increased calcium

false. that is IP3. DAG stays in membrane (hydrophobic) and activates protein kinase c

upon PIP2 cleavage and IP3 formation, what does IP3 do?

lands on IP3 gated calcium channels, releasing calcium from the ER

DAG is hydro_____ while IP3 is hydro_____. where do they reside?

DAG= hydrophobic (stay in plasma membrane)

IP3= hydrophilic (cytosol)

t/f: cAMP, cGMP, and calcium are all hydrophilic second messengers

true. all soluble in cytosol

what does DAG activate

protein kinase C

what does cAMP activate?

protein kinase A

functions of cAMP

1. intracellular second messenger

2. regulate ion channels

3. activate protein kinase A

4. regulate guanine nucleotide exchange factors

adenylate cyclase equation

ATP-> cAMP + PPi (makes cAMP)

phosphodiesterase equation

cAMP + H2O -> AMP (inactive)

which enzyme makes cAMP? breaks?

makes: adenylate cyclase

breaks: phosphodiesterase

protein kinase vs protein phosphatase

kinase: phosphorylates OH of serine, threonine, tyrosine to make ACTIVE protein

phosphatase: removes phosphate

how does protein kinase add a phosphate group

phosphorylates OH group of amino acids (serine, threonine, tyrosine)

nearly ________ protein kinases are encoded in the human genome

500

t/f: the activity of protein kinases and phosphatases regulate enzyme activity by activation and inactivation

true

which molecule does protein kinase remove a phosphate from in order to add to an amino acid

ATP-> ADP

how is protein kinase C activated and what does it do

activated by DAG, calcium, TPA; it is a kinase so it phosphorylates OH on amino acids

what activates protein kinase A? what does it do?

cAMP; phosphorylates enzymes

which molecule can activate protein kinase C without G protein stimulation

TPA= tissue plasminogen activator (goes right through membrane)

_____________ are the antagonists of protein kinases

protein phosphatases

t/f: phosphatases can activate a protein through dephosphorylation or they can dampen the effects of kinases

true

summarize GTP cell signaling transduction (big overview)

1. ligand lands on GPCR

2. alpha subunit+GTP dissociate

3. activates phospholipase C: PIP2-> DAG and IP3

-DAG [along w calcium, TPA] activates protein kinase C

-IP3 promotes calcium release

3. activates adenylate cyclase: ATP-> cAMP

-cAMP activates protein kinase A