Formation and Degredation of Glycogen- Rosenberg Flashcards
What tissues are insulin sensitive?
Most tissues (skeletal muscles, adipose tissue)
What tissues are insulin insensitive?
cornea, lense of the eye, liver, RBCs, WBCs, brain
Explain how GLUT4 and insulin work.
Insulin goes to the receptor and sends a signal to a vesicle containing GLUT4 receptors. The vesicle is translocated to the membrane surface by translocation proteins which are activated by protein kinase B (PKB). When insulin levels decrease, the vesicle invaginates back into the cell to be recycled.
Between meals, how does muscle still take in glucose?
When muscles contract, the conversion of ATP to ADP occurs. ADP then gets converted to ATP and AMP by adenylate kinase. The rise in AMP levels activates AMP KInase to phosphorylate translocation proteins.
Compare and Contrast Hexokinase and Glucokinase
Hexokinase:
Low Km levels, stronger affinity to glucose, non-insulin dependent, usually saturated with substrate, found in both liver and muscle cells, inhibited by its product
Glucokinase:
High Km levels, low affinity to glucose- needs a high concentration of glucose to be active, insulin induced, found only in liver cells, not inhibited
How does glucokinase regulated?
It is bound by GKRP in the nucleus of the liver cell until glucose levels rise. Also can be release by a rise in F1P. However, it is inhibited by F6P
Explain the process of creating a strand of glycogen without branching.
Glucose gets phosphorylated by glucokinase to G6P.
It then gets converted by G1P by phosphoglucomutase. After, UDP-glucose pyrophosphorylase adds a UDP and it becomes UDP glucose.
Glycogenin starts the chain, and glycogen synthase continues the chain
Explain the process of branching glycogen
Branching enzyme cleaves and adds 5-8 units at least 4 units into the chain from the non reducing end
Explain how to take apart glycogen
Glycogen phosphorylase works from the non-reducing end and breaks the alpha-1,4 bonds one at a time until reaching 4 units from the branch.
Transferase then comes over and moves 3 units to the larger non-reduced end of glycogen
Alpha-1,6 Glucosidase (Debranching enzyme) hydrolyzed the 1,6 bond to release one unit of glucose
Why can’t muscles cells convert glycogen all the way back to glucose?
Muscle cells lack glucose-6-phosphatase which converts G6P back to glucose
When is glycogen phosphorylase active?
When it is phosphorylated
When is glycogen synthase active or in the I form?
when it is unphosphorylated
What does glucagon do in glycogenolysis?
When combined with the receptor, activates a G protein to activate adenylate cyclase which changes ATP to cAMP.
cAMP then activates PKA which has four subunits that phosphorylate glycogen synthase, phosphorylase kinase, and inhibitor-1.
Phosphorylase kinase then phosphorylates glycogen physphorylase
Inhibitor-1 inhibits phosphotase
Can glucagon affect muscle cells?
No
Explain activation of Glycogenolysis by Epinephrine
Epinephrine can also use the cAMP pathway, but also uses the DAG and Ca pathway
Binds to receptors, activates phospholipase C that changes PIP to DAG and IP3
DAG activates protein kinase C (PKC) that phosphorylates glycogen synthase
IP3 allows the release of Ca. Ca combines with cadmodulin to activate phosphorylase kinase.
Phosphorylase kinase phosphorylates glycogen phosphorylase and glycogen synthase.
