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Z OLD ESA 1- Metabolism > Energy storage > Flashcards

Flashcards in Energy storage Deck (139):
1

What is the bodies preferred fuel?

Glucose

2

What is the result of glucose being the bodies preferred food source?

The body requires a constant level of glucose as an energy source

3

Which tissues have an absolute requirement for glucose as energy source?

- Erythrocytes (RBCs) and leukocytes 
- Testes
- Kidney medulla
- Lens and cornea of eye

4

Why is a stable glucose level required for normal brain function?

Because the brain prefers to use glucose as a fuel

5

Can the brain use any source other than glucose for fuel?

Yes, it can use ketone bodies, but not immediately

6

How long does it take for the brain to be able to utilise ketone bodies?

Oct-14

7

How much of the brains energy requirement can be obtained from ketone bodies?

~50%

8

What is required to enable blood glucose to be kept at required levels?

Store of glycogen

9

What form is glycogen stored in?

Granules

10

What cells have glycogen stores?

All of them to an extent

11

How is muscle glycogen present?

As both intra- and intermyofibrillar glycogen granules

12

How is liver glycogen stored?

As granules within hepatocytes

13

Describe the structure of glycogen

- Polymer consisting of chains of glucose residues
- Chains organised in branches 
- Residues linked by α-1,4- glycosidic bonds, with α-1,6-glycosidic bonds forming at branch points

14

Where to the branches in glycogen originate from?

A dimer of the protein glycogenin

15

What does the protein glycogenin act as in glycogen?

A primer at core of glycogen structure

16

How often are the branch points in glycogen?

Every 8-10 residues

17

What is the name given to glycogen synthesis?

Glycogenesis

18

Give the reactions that lead to the conversion of glucose to glycogen

- Glucose + ATP → glucose 6-phosphate + ADP
- Glucose 6-phosphate ↔ glucose 1-phosphate
- Glucose 1-phosphate + UTP + H 2 O → UDP-glucose + 2Pi 
- Glycogen (n resides) + UDP-glucose → glycogen (n+1 residues) +UDP

19

What enzyme is required for conversion of glucose to G-6-P?

Hexokinase

20

What is hexokinase called in the liver?

Glucokinase

21

What is the enzyme for the conversion of G-6-P to G-1-P?

Phosphoglucomutase

22

What is the enzyme for the addition of glycogen residues (in reaction 4)?

#NAME?

23

What does glycogen synthase do?

Adds α-1,4-glycosidic bonds

24

What does branching enzyme do?

Adds α-1,6-glycosidic bonds

25

What is the name given to glycogen degredation?

Glycogenolysis

26

Give the equations for glycogenolysis

- Glycogen (n residues) + Pi → G-1-P + glycogen (n-1 residues)
- G-1-P ↔ G-6-P

27

What is the enzyme used for removal of glycogen residues?

- Glycogen phosphorylase 
- or de-branching enzyme

28

What happens to G-6-P in muscle?

Glycolysis

29

What is happening when the muscle performs glycolysis on the G-6-P released from glycogen?

It is being used for local energy production

30

What happens to G-6-P in the liver?

Converted to glucose

31

What happens to the glucose produced from glycogen by the liver?

It is released into the blood for use by other body tissues

32

Is glycogenolysis just reversal of glycogenesis?

No

33

What is the result of glycogenolysis not being a simple reversal of glycogenesis?

Different enzymes allow for simultaneous inhibition of one pathway and stimulation of the other

34

Other than glycogenolysis, what other method does the liver have of producing G-6-P?

Gluconeogenesis

35

What is liver glycogen a buffer for?

Blood glucose concentration

36

How much of the liver mass is glycogen?

10%

37

What happens to the glucose in muscle?

It enters glycolysis, either being oxidised to CO 2 + ATP, or converted into lactate

38

What enzyme does the muscle lack?

G-6-Pase

39

What is the rate limiting enzyme in glycogen synthesis in the liver?

Glycogen synthase

40

What is the rate limiting enzyme in glycogen degradation?

Glycogen phosphorylase

41

In what fashion does glycogen metabolism regulation occur?

Reciprocal

42

What hormones regulate liver glycogen metabolism?

- Glucagon
- Adrenaline 
- Insulin

43

What effect does glucagon and adrenaline have on glycogen synthase?

Decreases enzyme activity

44

What effect does glucagon and adrenaline have on glycogen phosphorylase?

Increases enzyme activity

45

By what mechanism do adrenaline and glucagon affect the activity of enzymes?

Phosphorylation

46

What effect does insulin have on glycogen synthase?

Increases enzyme activity

47

What effect does insulin have on glycogen phosphorylase?

Decreases enzyme activity

48

By what mechanism does insulin affect the activity of enzymes?

De-phosphorylation

49

In what way does regulation of muscle glycogen differ from liver glycogen?

- Glucagon has no effect 
- AMP acts as an allosteric activator of muscle glycogen phosphorylase, but not liver form of enzyme

50

What are glycogen storage diseases?

Inborn errors in metabolism

51

What do glycogen storage diseases arise from?

Deficiency or dysfunction of enzymes of glycogen metabolism

52

How many distinct glycogen storage diseases are there?

11

53

What does the severity of a glycogen storage disease depend on?

The enzyme/tissue affected

54

What tissues can be affected by glycogen storage diseases?

Liver and/or muscle

55

How can someone have a disease in the liver or the muscle, but not both?

Glycogen phosphorylase is coded for by a different gene in liver than in the muscle, so it can be mutated in one but not the other

56

What can excess glycogen storage lead too?

Tissue damage

57

What can diminished glycogen stores lead to?

Hypoglycaemia and poor exercise tolerance

58

Give two examples of glycogen storage diseases

- von Gierkes disease 
- McArdles disease

59

What causes von Gierkes disease?

Glucose-6-phosphate deficiency

60

What causes McArdles disease?

Muscle glycogen phosphate deficiency

61

What is gluconeogenesis?

The production of new glucose not pre-exisiting stores in glycogen

62

When do we need to be able to synthesise new glucose?

When glycogen stores are low

63

What happens beyond ~8 hours fasting?

Liver glycogen stores start to deplete

64

Where does gluconeogenesis occur?

In liver, and to a lesser extent kidney cortex

65

How many major precursors for gluconeogenesis are there?

3

66

What are the 3 major precursors for gluconeogenesis?

- Lactate 
- Glycerol
- Amino acids

67

When is lactate produced?

In anaerobic glycolysis in exercising muscles and RBC’s

68

How does the process of gluconeogenesis using lactate occur?

Using the Cori Cycle

69

What happens in the Cori cycle?

- In the liver, 2 lactate molecules are converted to glucose 
- Glucose is transported from liver to muscle in the blood 
- In the muscle, glucose is converted into two lactate 
- The lactate produced in the muscle is transported in the blood to the liver

70

When is glycerol released?

From adipose tissue when triglycerides are broken down

71

What amino acids are used for gluconeogenesis?

Mainly alanine

72

Can acetyl~CoA be converted into pyruvate?

No

73

Why can’t acetyl~CoA be converted into pyruvate?

Because the pyruvate dehydrogenase reaction is irreversible

74

What is the result of the inability of acetyl~CoA to be converted into pyruvate?

There is no net synthesis of glucose from acetyl~CoA

75

How many reactions in gluconeogenesis are not simple reversions of corresponding steps in glycolysis?

3

76

What are the key enzymes in gluconeogenesis?

- Phosphoenolpyruvate carboxykinase (PEPCK)
- Fructose 1,6-bisphosphatease
- Glucose 6-phosphatease

77

Which of the key enzymes in gluconeogenesis are key sites of control for the pathway?

- Phosphoenolpyruvate carboxykinase (PEPCK)
- Fructose 1,6-bisphosphatease

78

What does PEPCK do?

Catalyses conversion of oxaloacetate to phosphoenolpyruvate

79

What does fructose 1,6-bisphosphatease do?

Catalyses conversion of fructose 1,6-bisphosphate to fructose 6-phosphate

80

What are the 2 key control enzymes in gluconeogenesis controlled by?

Hormones

81

What are the 2 key control enzymes in gluconeogenesis controlled in response to?

- Starvation 
- Prolonged exercise
- Stress

82

What hormones affect the action of the key control enzymes in gluconeogenesis?

- Glucagon 
- Cortisol 
- Insulin

83

What affect does glucagon and cortisol have on PEPCK?

Increases the amount

84

What effect does glucagon and cortisol have on fructose 1,6-bisphosphate?

Increased amount and activity

85

What is the overall effect of glucagon and cortisol on gluconeogenesis?

Stimulates

86

What effect does insulin have on PEPCK?

Decreases amount

87

What effect does insulin have on fructose 1,6-bisphosphate?

It decreases the amount and activity

88

What is the overall effect of insulin on gluconeogenesis?

Inhibits

89

How are lipids stored?

As triacylglycerols (TAGs)

90

What happens when energy intake is in excess of requirements?

It’s converted to triacylglycerol for storage

91

Are TAGs hydrophilic or hydrophobic?

Hydrophobic

92

How must TAGs be stored due to them being hydrophobic?

In anhydrous form in specialised tissue

93

What is the specialised storage tissue for TAGs?

Adipose tissue

94

Is TAG an efficient energy store?

Yes, highly

95

How does the energy content per gram differ in TAGs and carbohydrate/protein?

x2 more in TAG than in carbohydrate or protein

96

Under what conditions are TAG’s utilised?

#NAME?

97

How is storage and metabolism of TAGs controlled?

Hormones

98

Describe the structure of adipocytes

A large lipid droplet with cytoplasm and organelles pushed  to edge

99

What does the lipid droplet in adipocytes consist of?

Mainly TAG and cholesterol ester

100

How big are adipocytes?

~0.1mm in diameter, but expand as more fat is added

101

How much can adipocytes increase in size on weight gain?

About fourfold

102

What happens once adipocytes can’t expand anymore on weight gain?

They divide, increasing the total no. of fat cells

103

What is fatty acid synthesis called?

Lipogenesis

104

Where does lipogenesis occur?

Mainly in liver

105

What is the major source of carbon for lipogenesis?

Dietary glucose

106

How are fatty acids produced from glucose?

- Glucose is converted to pyruvate in the cytoplasm
- Pyruvate enters mitochondria, forms acetyl~CoA and OAA
- Acetyl~CoA and OAA condenses to form citrate 
- Citrate goes back to cytoplasm, and is cleaved back to acetyl~CoA and OAA
- Acetyl~CoA carboxylase produces malonyl~CoA from acetyl~CoA
- Fatty acid synthase complex builds up fatty acids by sequential addition of 2 carbon units provided by malonyl~CoA

107

What is the key regulator in fatty acid synthesis?

Acetyl~CoA carboxylase

108

What does the fatty acid synthesis process require?

Both ATP and NADPH

109

What increases fatty acid synthesis?

- Insulin 
- Citrate

110

By what mechanism does insulin increase fatty acid synthesis?

Covalent de-phosphorylation

111

By what mechanism does citrate increase fatty acid synthesis?

Allosteric activation

112

What decreases fatty acid synthesis?

Glucagon/adrenaline and AMP

113

By what mechanism do glucagon and adrenaline decrease fatty acid synthesis?

Covalent phosphorylation

114

By what mechanism does AMP decrease fatty acid synthesis?

Allosteric inhibition

115

What is the difference in the purpose cycle of reactions between FA oxidation and FA synthesis

- In FA oxidation, the cycle of reactions remove C 2
- In FA synthesis, the cycle of reactions add C 2

116

What is the difference in how is the C 2 is transferred in FA oxidation and FA synthesis?

- In FA oxidation, C 2  removed as acetyl~CoA
- In FA synthesis, C 2 added as acetyl~CoA

117

Which of FA oxidation or FA synthesis produced acetyl~CoA, and which consumes it?

#NAME?

118

What is the difference in the site of FA oxidation and FA synthesis?

- Oxidation occurs in mitochondria 
- Synthesis occurs in cytoplasm

119

What is the difference in the enzymes used in FA oxidation and synthesis?

#NAME?

120

Is FA synthesis oxidative or reductive?

Reductive

121

What is the result of FA synthesis being reductive?

It requires NADPH

122

What is the difference in ATP requirement between FA oxidation and synthesis?

#NAME?

123

What is the difference in what the intermediates are linked to in FA oxidation and synthesis?

#NAME?

124

What is the difference in regulation between FA oxidation and synthesis?

- Oxidation is regulated indirectly by availability of fatty acids in mitochondria
- Synthesis is regulated directly by activity of acetyl~CoA carboxylase

125

What is the difference in reaction to glucagon and adrenaline between FA oxidation and synthesis?

#NAME?

126

What is the difference in reaction to insulin between FA oxidation and synthesis?

#NAME?

127

What is the process of fat mobilisation called?

Lipolysis

128

Give the equation for lipolysis

Triacylglycerol (in adipose tissue) → glycerol (in blood)  + free fatty acids

129

What enzyme catalyses lipolysis?

Hormone sensitive lipase

130

What hormones is hormone sensitive lipase regulated by?

#NAME?

131

What is the effect of glucagon and adrenaline on hormone sensitive lipase?

Stimulates

132

By what mechanism does glucagon and adrenaline stimulate hormone sensitive lipase?

Phosphorylation

133

What is the effect of insulin on hormone sensitive lipase?

Inhibited

134

By what mechanism does insulin inhibit hormone sensitive lipase?

Dephosphorylation

135

Where does the glycerol in the blood produced by lipolysis go?

To liver

136

What happens to glycerol in the liver?

It’s utilised as a carbon source for gluconeogenesis

137

How do free fatty acids travel in the blood?

Complexed with albumin

138

Where do free fatty acids in the blood go?

Muscle and other tissues

139

What happens to free fatty acids in the muscle and other tissues?

ß-oxidation