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Lecture

lec28 soon-yi part 2 glycogenolysis


Department
Biochemistry
Course Code
BCH210H1
Professor
Michael Baker

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BIO210H1
LECTURE 28
Case Study: Soon-yi Part II: Accessing Glycogen Stores
1. Glycogen
2. Glycogenolysis: Role of Adrenaline and Glucagon
3. Glycogen Phosphorylase
4. Differences Muscle vs. Liver
Soon-Yi II Beach Running/Accessing Glycogen Stores
- As Soon-yi begins to run over the sand, her existing blood glucose cannot
readily sustain muscle glycolysis
oShe needs more fuel for glycolysis, and her muscle glycogen will
provide this
Glycogen
- Glycogen = a polymer of glucose is found in granules in muscle and liver
cytoplasm
oStore glucose to support sugar in muscle and liver
- Has α(14) links as well as α(16) branch points
oStructurally similar to mylopectin, but more branched
- Glycogen is a polymer of glucose found in cytoplasm and in granules in
muscle and liver
- Before races marathon runners try to maximize muscle glycogen, as this is
very important fuel in muscle
oEfficiency in running varies directly in amount of glycogen you can
store in cells
oTake up a lot of carbohydrates, so you can get through the race
oMuscles are adapted in using different fuels at the same time
oHave to keep glycogen going until right at the end of race
Fat is energy rich, but efficiency goes down if just using fat
oMust use it strategically
- Soon-yi has not eaten for 10 hours: as her blood glucose level dips, she
releases two hormones into her blood
oIf blood sugar goes down, body responds
Autonomic response comes from hormones
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BIO210H1
LECTURE 28
Glycogen: Polyglucose in Muscle and Liver
- NOTE: Highly branched glycogen structure
Glycogenolysis
-
Receptors on surface of cells
- Can get cell signal/signal transduction when biologically active compound can
bind to receptor and cause changes inside cell
- Two hormones:
oEpinephrine
Adrenalin
Glucagon
Small peptide hormone released from pancreas in
response to dropping blood sugar
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BIO210H1
LECTURE 28
- Epinephrine and adrenergic receptor
oStarts a signal cascade, amplify
oCascade triggers enzymes, which triggers more enzymes...etc.
Enzyme can make thousands of products
oMajor amplification – muscles are electrified
- Adrenaline interacts with receptors on Soon-yi’s muscle cells and activates an
intracellular signal pathway
oThis triggers a rise in cAMP
- cAMP is made from ATP via adenylate cyclase (AC)
ocAMP is a “second messenger” as adrenaline does not enter the
muscle cell
oAdrenaline’s agent inside cell is cAMP (small compound derivative of
ATP)
- cAMP initiates a cascade of enzyme activation in the muscle cytoplasm
- cAMP first activates protein kinase A (PKA)
- Amplification mechanism
oThousands of PKA turning on, which activates thousands of targets
PKA – enzyme that phosphorylates other proteins at Ser and Thr
residues, using ATP
Addition of P change in conformation leads to activation
PKA activates/phosphorylates enzyme called
phosphorylase kinase
- Phosphorylase kinase is activated in this way by PKA in Soon-yi’s muscle cells
- Calcium also activates phosphorylase kinase
- Calcium ions rise in muscle cells to stimulate contraction
oContracting muscles by releasing Ca
- Phosphorylase kinase then activates glycogen phosphorylase b (GPb)→
glycogen phosphorylase a (GPa) by phosphorylation
oSwitching from b to a (inactive active)
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