Maintaining Blood Glucose Levels_Molecules Flashcards Preview

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Flashcards in Maintaining Blood Glucose Levels_Molecules Deck (89):
1

What conducts hormonal regulation in skeletal muscle?

Catecholamines

2

What is catecholamines?

Adrenaline /Noradrenaline a.k.a epinephrine / norephinephrine

3

What does catecholamines do?

1) Act to stimulate phosphorylation of enzymes
2) Stimulate glycogen breakdown in liver and muscle, when fuels need to be mobilised for the energy needs of muscle (block synthesis)
3) Stimulate cAMP synthesis through beta-adrenergic receptors and raise the cytoplasmic calcium concentration through alpha1-adrenergic receptors
4) Act to increase levels of fructose 2,6-biphosphate -> stimulate glycolysis

4

Where are alpha1-adrenergic receptors found?

prevail in the liver

5

Where are beta-adrenergic receptors more important in?

Muscle tissue

6

What does the calcium released by the catecholamines do?

Stimulate phosphorylase kinase synergistically with cAMP

7

What does insulin do?

1) Stimulate glycogen synthesis in liver and skeletal muscle
2) Stimulates dephosphorylation
3) Ensures that excess carbohydrate is stored away as glycogen after a meal.
4) Through the protein kinase B cascade, it regulates glycogen metabolism

8

What is the reciprocal regulation that happens in the liver?

Phosphorylation and dephosphorylation of enzymes

9

What stimulates dephosphorylation?

Insulin

10

What stimulates phosphorylation?

Glucagon

11

What is glycogen metabolism when there is high blood glucose?

Insulin activates glycogen synthesis and blocks glycogen breakdown

12

What is glycogen metabolism when there is low blood glucose?

Glucagon blocks glycogen synthesis and activates glycogen breakdown

13

What is ATP from glucose used for?

Major energy source for all cells

14

Aerobic breakdown of glucose yields how many ATP?

30 - 32 ATP

15

Anaerobic breakdown of glucose to lactate yields how many ATP?

2 ATP

16

What are the tissue requirements for glucose?

1) Cells without mitochondria
2) Cells of the nervous system - do have mitochondria
3) Require a continual supply of glucose from the bloodstream

17

What is the relationship of cells without mitochondria and glucose?

Absolute dependence on glucose for energy needs

18

Anaerobic glycolysis creates how many ATP?

2 ATP

19

Do cells of the nervous system have mitochondria?

Yes

20

What is the relationship of cells of the nervous system and glucose?

cells of the nervous system have high energy need: approx. 20% of the body's oxygen and 60% of body's glucose consumed by the brain

21

What is the relationship between glucose and the brain?

Glucose is sole energy source used by the brain in normal condition

22

What are examples of different tissue that require glucose?

1) Cardiac muscle
2) Adipose tissue
3) Skeletal muscle

23

What tissue can utilise glucose or fatty acid?

Muscle and adipose tissue

24

What is muscle and adipose tissue utilising glucose or fatty acid dependent on?

on the level of glucose in the bloodstream

25

What is the ideal level of glucose in the bloodstream?

Maintained between 4 - 10mM

26

What happens after a meal?

High blood glucose level

27

How does the body compensate for high blood glucose levels after a meal?

Insulin released from the pancreas

28

What is glucose uptake by tissue via?

Glucose transporters (GLUTs)

29

Where are the glucose transporters found?

on brain, RBC, liver, kidney, etc.
continually present at cell surface

30

Is there glucose transporters found on muscle and adipose tissue?

Yes

31

What is GLUT-4?

Insulin sensitive and is the glucose transporter found on the muscle and adipose tissue

32

What does GLUT-4 do?

Take up glucose when glucose levels in blood are high - reduce glucose levels

33

What is the "Fed" State?

period after the meal when there is high blood glucose level

34

What does insulin act to do in "fed" state

1) Stimulate glucose uptake by muscle and adipose tissue
2) Increase glycolysis
3) Increase glycogen synthesis (liver and skeletal muscle)

35

What happens in the liver during "fed" state?

Excess glucose used for
1) Glycogen synthesis
2) Synthesis of fatty acids - via glycolysis

36

What happens in the skeletal muscle in "fed" state?

Excess glucose used for glycogen synthesis

37

What happens in the cardiac muscle in "fed" state?

Increased glucose used to supply ATP for cell's own needs - switches from using fatty acids

38

What happens in adipose tissue in "fed" state?

Excess glucose used to syntheses triglycerides for storage via glycolysis

39

What increase in response to insulin?

Fructose-2,6-biphosphate levels increase

40

What happens when Phosphofructokinase-1 increase?

Overrides effects of ATP, citrate thus increasing glycolysis

41

What is acetyl CoA produced used to do?

Synthesise fats for storage

42

What are the three stage of glycogen synthesis?

1) Priming
2) Elongation
3) Branching

43

What happens in the priming stage of glycogen synthesis?

Energy input

44

What happens in the elongation stage of glycogen synthesis?

Addition of glucose to the non-reducing ends of alpha 1 - 4 chains

45

What happens in the branching stage of glycogen synthesis?

Formation of alpha 1 - 6 branch points

46

What happens in glycogen synthesis?

Enzymes embedded in the outer branches of the glycogen granule

47

What is UDP glucose?

"activated" glucose used in biosynthetic reactions

48

What is formed at the end of the priming stage of glycogen synthesis?

UDP Glucose

49

What is glycogen synthase?

Major regulatory enzyme in glycogen synthesis

50

What is glycogen synthase stimulated by?

By cellular levels of Glc-6-P

51

What stimulates a decrease in blood glucose?

Effects of insulin stimulate a decrease in blood glucose

52

What happens when insulin is released?

Blood glucose level drop
Glucagon released from pancreas
Go into fasting state

53

What is the fasting state?

Low blood glucose in the body

54

What happens when the body goes into fasting state?

Insulin levels drop
Glucagon acts on the liver

55

What happens when insulin levels drop?

1) Muscle and adipose tissue stop taking up glucose (GLUT-4 no longer expressed on cell surface)
2) "Spares" glucose for use of cells that requires it most

56

What happens when glucagon acts on the liver during fasting state?

Glucagon acts on the liver to:
1) Decrease glycolysis
2) Breakdown glycogen
3) Increase gluconeogenesis,
releasing glucose into the blood stream

57

What is glycogen phosphorylase?

Major regulatory enzyme in glycogen degradation

58

What happens during glycogen degradation?

Glc-1-P converted to Glc-6-P by phosphoglucomutase (PGM)

59

What does phosphoglucomutase do?

Catalyses the interconversion between Glc-1-P and Glc-6-P (both ways)

60

What is the allosteric control of glycogen degradation?

Glycogen Phosphorylase

61

What happens in relationship to glycogen degradation in muscle tissue?

Inhibited by Glc-6-P and ATP; activated by AMP (glycogen in muscle used solely for muscle's own energy needs)

62

What does glycogen phosphorylase do in liver tissue?

Inhibited by glucose in liver tissue

63

What does liver do after a carbohydrate meal?

Synthesize glycogen and degrade it to free glucose during fasting

64

What happens in the liver during glycogen degradation?

G-6-P from glycogen breakdown is cleaved to free glucose by G-6-P, and the glucose is released into the blood for use by needy tissue including brain and blood cell

65

What does skeletal muscle do in regards to glycogen degradation?

Synthesise glycogen at rest and degrades it during exercise

66

Why can't muscle produce free glucose?

No Glucose-6-phosphatase

67

How does muscle metabolise glucose - 6 - phosphate?

By glycolysis forming lactate.

68

What does muscle glucose degradation form lactate?

Because glycogen degradation produces G-6-P without consuming ATP, anaerobic glycosides from glycogen produces three rather than two molecules of ATP for each glucose residue

69

What is the difference in liver and muscle glycolysis degradation?

liver glycogen:
- synthesised and degraded in response to feeding and fasting, therefore its level fluctuates widely in the course of a typical day
muscle glycogen:
- fairly constant and becomes depleted only during vigorous and prolonged physical exercise.

70

What enzymes are used in glucagon in the liver?

Phosphorylase kinase phosphorylates both glycogen phosphorylase and glycogen synthase.

71

What happens to the liver glycogen stores in the fasting state?

Depleted after approximately 24 hour of fasting

72

What happens when the liver glycogen store is depleted after 24 hours of fasting?

Subsequently rely on gluconeogenesis to maintain blood glucose levels

73

What are the different genetic deficiencies in relation to glucose and glycogen?

1) Glycogen storage disease
2) Von Gierke disease
3) McArdle disease

74

What is the McArdle disease?

Deficiency of glycogen phosphorylase in muscle tissue

75

What is Von Gierke disease?

G-6-phosphatase deficiency - inability to convert Glc-6-P to glucose in liver
(Type 1 Glycogen storage disease)

76

What is glycogen storage diseases?

deficiencies in enzymes involved in glycogen degradation

77

What are the two forms of glycogen storage diseases?

1) Hepatic Forms
2) Myopathic forms

78

What happens in the hepatic form of glycogen storage disease?

Fasting hypoglycemia
Liver damage

79

What happens in the myopathic form of glycogen storage disease?

Muscle weakness and wasting

80

how many enzymes does gluconeogenesis use?

7 of the 10 enzymes - catalysed reactions of glycolysis

81

How does gluconeogenesis happen?

Specific 'by-pass' reactions at the 3 regulatory steps of glycolysis

82

How many ATP does gluconeogenesis consume?

6 ATP

83

Name the regulatory enzyme in gluconeogenesis

1) Pyruvate Carboxylase
2) Fructose 1,6 biphosphatase
3) Glucose - 6 - phosphatase

84

What happens in Von Gierke disease?

- Glc-6-P from glucose breakdown AND gluconeogenesis not converted to glucose
- no glucose released from liver to replenish blood glucose levels
- Profound fasting hypoglycaemia

85

How is the patient kept alive when they have Von Gierke Disease?

By regular carbohydrate feeding, day and night
Nocturnal gastric infusions of glucose or uncooked corn starch

86

What is the hormonal regulation in the liver during glycolysis and gluconeogenesis?

Fructose 2,6 biphosphate

87

What is fructose 2,6 diphosphate?

Molecule via which insulin and glucagon influence glycolysis and gluconeogenesis in the liver

88

What happens to glycolysis and gluconeogenesis when there is high cellular levels?

Glycolysis 'on'
Gluconeogenesis 'off'

89

What is the cellular levels determined by?

By activity of a protein that has two enzyme activities (bifunctional)