Formation and Degradation Of Glycogen Flashcards
Which tissues are insulin-sensitive?
Most tissues like adipose and muscles tissue (which use GLUT-4)
Which tissues are insulin-insensitive
Erythrocytes, leukocytes, lens of eye, cornea, liver (GLUT-2), and brain
What does insulin-insensitive mean?
That they don’t need insulin in order to take in glucose
What happens after a meal and blood glucose levels rise and insulin is secreted?
Insulin binds to membrane causing GLUT-4 to go to cell membrane to allow glucose in cell. Insulin-stimulated translocation of GLUT-4 involves the activation of protein kinase B (PKB). Active PKB phosphorylates protiens involved in GLUT-4 translocation.
What happens between meals when the insulin levels decline?
Glucose uptake by muscle is stimulated by the increase in AMP levels and the subsequent activation of AMP-stimulted protein kinase (AMPK). AMPK activation promotes the translocation of GLUT-4 transporters to muscle membrane. AMP is generated in the adenylate kinase reaction
Why is the phosphorylation of glucose important?
It is significant because glucose-6-phosphate cannot pass through the membrane to the extracellular side, since it is not a substrate for the glucose transporters. Thus, glucose-6-phosphate is trapped inside the cell and is committed to further metabolism. It also creates a favorable gradient so glucose continues to enter cell.
Describe basics of hexokinase.
Km = 0.2 mM. Constitutive enzyme. Found in most tissues. Strongly inhibited by the product glucose-6-phosphate.
Describe basics of glucophosphate.
Km = 10 mM. Induced enzyme (insulin is the inducer). In liver and pancreas. Not inhibited by glucose-6-P.
What does the glucokinase regulating protein (GKRP) do?
It binds to glucokinase to inactivate it. It releases glucokinase when glucose levels increase.
Activation of Glycogenolysis by cAMP-directed Pathway:
1. ? 2. This enzyme converts cytoplasmic ATP into cAMP which binds to a cytoplasmic enzyme, protein kinase A (PKA).
- Glucagon binding to the glucagon receptor in the liver activates adenylate cyclase, via G-proteins.
Activation of Glycogenolysis by cAMP-directed Pathway:
1. Glucagon binding to the glucagon receptor in the liver activates adenylate cyclase, via G-proteins. 2. ?
- This enzyme converts cytoplasmic ATP into cAMP which binds to a cytoplasmic enzyme, protein kinase A (PKA).
Activation of Glycogenolysis by cAMP-directed Pathway:
1. Glucagon binding to the glucagon receptor in the liver activates adenylate cyclase, via G-proteins 2. This enzyme converts cytoplasmic ATP into cAMP which binds to a cytoplasmic enzyme, protein kinase A (PKA). 3.?
- cAMP activates PKA by binding to its regulatory subunits and releasing the active catalytic subunits.
Activation of Glycogenolysis by cAMP-directed Pathway:
2. This enzyme converts cytoplasmic ATP into cAMP which binds to a cytoplasmic enzyme, protein kinase A 3. cAMP activates PKA by binding to its regulatory subunits and releasing the active catalytic subunits. 4.?
- PKA activates phosphorylase kinase by phosphorylation, which in turn, phosphorylates glycogen phosphorylase b, thereby converting it to the active phosphorylase a
Activation of Glycogenolysis by cAMP-directed Pathway:
3. cAMP activates PKA by binding to its regulatory subunits and releasing the active catalytic subunits. 4. PKA activates phosphorylase kinase by phosphorylation, which in turn, phosphorylates glycogen phosphorylase b, thereby converting it to the active phosphorylase a. 5. ?
- PKA also phosphorylates glycogen synthase, thereby decreasing its activity. Glycogen synthase has nine serine residues that can be phosphorylated by other kinases.
Activation of Glycogenolysis by cAMP-directed Pathway: 4. PKA activates phosphorylase kinase by phosphorylation, which in turn, phosphorylates glycogen phosphorylase b, thereby converting it to the active phosphorylase a. 5. PKA also phosphorylates glycogen synthase, thereby decreasing its activity. Glycogen synthase has nine serine residues that can be phosphorylated by other kinases. 6.?
6.PKA also phosphorylates inhibitor-1, a protein phosphatase inhibitor protein, thereby making it active. Phosphorylated inhibitor-1 inhibits phosphoprotein phosphatases.
