Dr. Kilberg - Glucose Flashcards
What is the difference between a steroid and a hormone signaling system?
Steroids diffuse across the nuclear membrane directly.
Hormones enter nucleus via transport proteins.
**They both bind nuclear DNA and alter transcription***
What are some of the characteristics of a tyrosine kinase?
- Hormone / Growth (insulin) factor binds to membrane bound receptor
- Self phosphorylation on tyrosine residue
- Kinase cascade follows
- GLUT 4 mobilized into cell membrane
- Uptake of glucose
Describe the inisitol of G-Protein activity.
Inisitol Phosphate Signaling
- Binding to surface receptor
- Activation of G protein relay GDP–>GTP
- Release of secondary messenger
- Increases Ca+
- Ca+ activates protein kinase
- Kinase activity increases intracellular effects
Describe the G-Protein cAMP signaling process?
- Hormone binds (Glucagon)
- Receptor changes shape and interacts
- Gs subunit binds to receptor
- GDP –> GTP swap
- Adenlylate Cylase activated
- Reverse process to inactivate on Gi subunit (except hydrolysis)
What pancreatic cells release insulin?
Beta cells
Where does GLUT 4 exist?
In muscle and adipose tissue.
How is the stimulatory subunit of the g-protein complex used to regulate adenylate cyclase production?
Activation is on the Ga-Subunit and includes a GDP->GTP replacement.
Deactivation of the Gs-subunit is by loss of the stimulatory ligand and the subsequent hydrolysis of GTP to GDP.
What does adenylate cyclase make?
It makes cAMP (cyclic AMP)
What does cAMP activate?
It activates PKA (protein kinase A)
Once PKA is activate by cAMP what happens?
PKA phosphorylation of cellular protein on serine and threonine residues activates intracellullar response to the original ligand binding.
What enzyme breaks down cAMP?
cyclic nucleotide phosphodiesterase
If you inhibit the breakdown of cAMP what happens?
We sustain the cellular response to the original ligand.
What inhibits the breakdown of cyclic nucleotide phosphodiesterase?
Caffeine
PKA structure?
- 4 subunits
- 2 regulatory / 2 catalytic
- 4 binding sites for cAMP on regulatory subunits
- Release of catalytic subunits
Where and on what subunit does pertussis act?
It acts on the G-inhibitory subunit in the lungs
How does the pertussis toxin work?
It blocks the activation of the inhibitory subunit by blocking the GDP –> GTP transfer. This is by ADP-Ribosylation (the addition of the ADP-Ribose to the inhibitory subunit blocks GDP –> GTP transfer)
With this always inactivet the stimulatory subunit runs away affecting Na+/ H2O balance / tranfer in the lung.
Where and on what subunit does the cholera toxin work?
Cholera works on the G-stimulatory subunit by ADP-ribosylation of the stimulatory subunit when it is active. This means it can’t be deactivated. This is present in the GI tract.
What is the difference between pertussis and cholera toxin activity?
Pertussis - ADP-rybosylation of the inhibitory subunit in the GDP state so that it can’t be activated via GDP –> GTP transfer.
Cholera - ADP-Ribosylation of the stimulatory subunit in the active state blocking the ATP–> ADP hyrdrolysis process and leaving the stimulatory subunit active.
Where does insulin bind on what?
It bind on the alphaunit of the membrane bound tyrosine kinase.
Step 2 of insulin pathway?
Autophosphrylation of the beta-subunit of the tyrosine kinase. This is on a tyrosine residue.
Step 3 of insulin pathway?
Phosphorylation of a tyrosine residue on IRS-1 (insulin receptor substrate) this activates IRS-1 and a kinase cascade that activates cellular proteins and effects.
What transporter is affected by insulin?
GLUT4 (the only one)
Where does GLUT 4 exist?
Adipose and Muscle (primary site of insulin reaction and GLUT 4 mobilization)
Other than glucose regulation in the blood what does insulin do?
It acts as a growth factor
What are the two dietary sugars?
Lactose and Sucrose
What are the dietary sugars broken into?
Glucose and Fructose
What happens to glucose in the cytoplasm?
Glucose –> Pyruvate via glycolysis
How many ATP come out of glycoysis?
2 NADH + 4ATP
Each NADH = 3 ATP
It costs 2 ATP
NET ATP = 8 ATP