hormonal regulation Flashcards
glucagon
-Peptide hormone produced by α-cells of the pancreas
-Released upon the drop in blood glucose levels.
-Raises the concentration of glucose and fat in the blood stream.
-Binds to a G-protein-coupled receptor (glucagon receptor), which activates G S (adenylate cyclase stimulator)
cyclic AMP
-second messenger
-produced from ATP by adenylate
-hydrolyzed by phosphodiesterase
-Activates cAMP-dependent protein kinase (protein kinase A).
-Protein kinase A phosphorylates many proteins.
6-phosphofructo-2-kinase/fructose 2,6-
bisphosphatase
-Bifunctional enzyme with both kinase and
phosphatase activity.
-Controls the concentration of fructose 2,6-
bisphosphate, an allosteric effector, which
activates 6-phosphofructo-1-kinase and
suppresses fructose 1,6-bisphosphatase
Fructose 2,6-bisphosphate _______ glycolysis and ______ gluconeogenesis
increases and suppresses
6-phosphofructo-2-kinase/fructose 2,6-
bisphosphatase in liver
-In liver, phosphorylation by protein kinase A switches
the enzyme from a kinase to a phosphatase, decreasing
fructose 2,6-P 2 level.
-Epinephrine also increases cAMP, showing the same effects
in the liver as glucagon.
-Upon the release of glucagon or epinephrine, liver
releases glucose to the blood stream
6-phosphofructo-2-kinase/fructose 2,6-
bisphosphatase in heart
-Heart has an isoenzyme different from the liver enzyme.
-Phosphorylation by protein kinase A switches the
isoenzyme from a phosphatase to kinase.
-Epinephrine increases fructose 2,6-bisphosphate, which stimulates glycolysis.
inactivation of pyruvate kinase in liver
-Protein kinase A inactivates pyruvate kinase.
-Phosphoenolpyruvate is not converted to pyruvate
but used for gluconeogenesis
_____ and _____ stimulate glycogen breakdown in liver
glucagon and epinephrine
induction of gluconeogenic enzymes in the liver
-Induction of enzymes results in long-term effects
on metabolism.
-Protein kinase A phosphorylates cAMP-response
element binding protein (CREB), a transcription
factor.
-Activated CREB binds to cAMP-response element
(CRE), a cis acting element within the regulatory
region of genes responsive to cAMP.
-Genes for PEP carboxykinase, fructose 1,6-
bisphosphatase, glucose 6-phosphatase are
responsive to cAMP.
-Glucagon also represses the expression of
glucokinase, 6-phosphofructo-1-kinase, and pyruvate
kinase
By phosphorylation, protein kinase A _____ glycogen phosphorylase and
_____ glycogen synthase
activates and inactivates
stimulation of glycogen breakdown in the liver
-Activated glycogen phosphorylase breaks
down glycogen to glucose-1-phosphate.
-Because protein kinase A also suppresses
glycolysis in liver, glucose is readily released
to the blood stream
What does all of this?
-Peptide hormone produced by β-cells of the pancreas
-Released upon the raise in blood glucose levels.
-Reduces the concentration of glucose in the blood stream.
-Binds to a receptor tyrosine kinase
-Promotes glucose uptake, glycogen synthesis, glycolysis, and fatty acid
synthesis
insulin
mechanism of insulin action
-Opposes the actions of glucagon and epinephrine.
-Activates cAMP phosphodieterase, which lowers cAMP
levels.
-Activates phosphoprotein phosphatase, which reverses
the action of protein kinase A.
-Dephosphorylation converts fructose 2,6-bisphosphatase to
6-phosphofructo-2-kinase.
-Dephosphorylation activates pyruvate kinase
hormonal regulation of lipid membranes
-Glucagon promotes fatty acid oxidation.
-Insulin promotes fatty acid synthesis.
glucagon
-promotes fatty acid oxidation
-Increases in triacylglycerol breakdown by phosphorylation of hormone-
sensitive lipase.
-Suppress acetyl CoA carboxylase by phosphorylation.
