Lecture 21: Glycogen Coordination & Fuel Metabolism Flashcards Preview

SMP - MNE Exam 2 > Lecture 21: Glycogen Coordination & Fuel Metabolism > Flashcards

Flashcards in Lecture 21: Glycogen Coordination & Fuel Metabolism Deck (63)
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31

What is the NTP usually used in glycogen synthesis? Which phosphoanydride bond is attacked?

UTP
The α one

32

Describe the de novo glycogen synthesis pathway.

PRIMER SYNTHESIS catalyzed by glycogenin:
1. Tyr residue attacks C1 of NDP-glucose (NDP released)
2. Glucosyltransferase activity: (-OH) on C4 attacks C1 of another NDP-glucose (NDP released)
--> done until primer has 8-10 glucose

BRANCHING catalyzed by glycogen branching enzyme:
1. Straight-chain series cleaved off
2. Energy released from
α-1,4 bond used to make α-1,6 linkage and heat released

33

Is glycogen branching enzyme regulated by hormones?

NOPE

34

Describe the activation of glycogen phosphorylase.

Phosphorylase kinase phosphorylates glycogen phosphorylase b with 2 ATP = glycogen phosphorylase a + 2 ADP

35

Describe the deactivation of glycogen phosphorylase.

Phosphoprotein phosphatase-1 (PP1) hydrolyzes the 2 phosphate groups on glycogen phosphorylase a with 2 H2O = glycogen phosphorylase b + 2 Pi

36

What are the 4 stimulators of phosphorylase kinase in liver and muscle? How does each work?

LIVER:
1. Glucagon (through PKA)
2. Epinephrine (through PKA)

MUSCLES:
1. Epinephrine (through PKA)
2. Ca2+ (allosteric)
3. AMP (allosteric)

37

Describe the activation of phosphorylase kinase by glucagon/epi.

Protein kinase A (PKA) phosphorylates phosphorylase kinase b with 2 ATP = phosphorylase kinase a + 2 ADP

38

Describe the deactivation of phosphorylase kinase.

Phosphoprotein phosphatase-1 (PP1) hydrolyzes the 2 phosphate groups on phosphorylase kinase a with 2 H2O = phosphorylase kinase b + 2 Pi

39

How is PKA regulated?

Hormonally via cAMP -
activated by:
1. Glucagon
2. Epinephrine

40

Describe the activation of glycogen synthase.

Phosphoprotein phosphatase-1 (PP1) hydrolyzes the 2 phosphate groups on glycogen synthase b with 2 H2O = glycogen synthase a + 2 Pi

41

Describe the deactivation of glycogen synthase.

Glycogen synthase kinase-3 (GSK-3) using 3 ATP/PKA using 1 ATP/CKII using 1 ATP/phosphorylase kinase using 2 ATP, can ALL phosphorylate glycogen synthase a = phosphorylase kinase a + 2 ADP

42

What inhibits GSK-3?

Insulin

43

What is phosphoprotein phosphatase-1 (PP1) stimulated by? Explain the last 2

1. Insulin
2. G6P (from G1P broken down by glycogen phosphorylase)
3. Glucose (from glucose broken down by debranching enzyme)

44

What is dephosphorylation of glycogen synthase by phosphoprotein phosphatase-1 (PP1) inhibited by?

1. Glucagon
2. Epinephrine

45

What are the 3 fuels that skeletal muscle can use?

1. Glucose
2. FAs
3. Ketone bodies

46

Main fuel source of adipose tissue?

Glucose

47

Where are FAs mainly synthesized?

The liver

48

At what glucose blood concentration does neural dysfunction occur?

Below 2.5 mM

49

What fuel does the liver use?

α-Ketoacids

50

How does the liver avoid using glucose? What other purpose does this serve?

It uses glucokinase (hexokinase 4) instead of hexokinase, which has a high Km and lowe Vmax, so it does not compete with other organs for glucose when glucose is low

Also allows prevention of glucose phosphorylation before it goes through GLUT2

51

What is necessary to cross the BBB?

Hydrophilicity!

52

What are the 2 places where we find glycogen?

1. Muscles
2. Liver

53

Can muscles break down glycogen for glucose homeostasis?

NOPE

54

After how many hours are glycogen stores COMPLETELY depleted?

24 hrs

55

After how long are the muscle glycogen stores depleted?

Depends on level activity, but after enough starvation hours it's broken down so that the lactate can be converted to alanine for gluconeogenesis

56

Which phosphate linkage contains more energy: G1P or G6P?

G1P

57

Is the conversion of G1P to G6P reversible? Why?

Yes because the difference in energy between G1P and G6P is small

58

How much of the muscle glycogen can be RAPIDLY mobilized?

About 50% before branching

59

Why does debranching enzyme transfer a triose and then hydrolyze the 1,6 bond instead of debranching the whole 4 glucose?

Thermodynamics: alpha 1,4 bonds contain more energy than alpha 1,6 so it would be endothermic to cleave the 1,6 to form a new 1,4 bond

60

Is energy released or consumed to make glycogen 1->4 linkages? How is this made up for in skeletal muscle?

Consumed but made up in skeletal muscle because the first step of glycolysis will be bypassed (usually uses 1 ATP)