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ESA2 - Metabolism, Endocrinology and Haematology > Energy Storage > Flashcards

Energy Storage Flashcards

1
Q

Which tissues have an absolute requirement for glucose?

A

Red blood cells, neutrophils, innermost cells of kidney medulla, lens of the eye

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2
Q

What is glucose stored in the form of?

A

Glycogen

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3
Q

Below what level of blood glucose would a patient experience confusion?

A

2.8mmol/L and below

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4
Q

Below what level of blood glucose would a patient experience weakness and nausea?

A

1.7mmol/L and below

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5
Q

Below what level of blood glucose would a patient experience muscle cramps?

A

1.1mmol/L and below

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6
Q

Below what level of blood glucose would cause brain damage/death?

A

0.6mmol/L

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7
Q

Which two cell types store glycogen?

A

Muscle and liver

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8
Q

What is the difference between muscle and liver glycogen?

A

Muscle glycogen just supplies muscle while liver glycogen can supply the rest of the body

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9
Q

What is glycogen?

A

A polymer consisting of chains of glucose residues

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10
Q

Which type of bonds join chains in glycogen?

A

Alpha 1-4 glycosidic bonds

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11
Q

Which bond types form branch points in glycogen?

A

Alpha 1-6 glycosidic bonds

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12
Q

Where do the branches in glycogen originate?

A

From a dimmer of the protein glycogenin

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13
Q

How frequent are the branch points in glycogen?

A

Every 8-10 residues

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14
Q

Does synthesis of glycogen require energy???

A

Yes

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15
Q

What are the four steps of glycogenesis?

A

1) Glucose to Glucose-6-phosphate
2) Glucose-6-phosphate to Glucose-1-phosphate
3) Glucose-1-Phosphate to UDP glucose + PPi
4) UDP glucose + Glycogen(n residues) to Glycogen(n+1 residues) + UDP

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16
Q

Which enzyme converts glucose into glucose-6-phosphate in the first step of glycogenesis?

A

Hexokinase or glucokinase (in liver)

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17
Q

Which enzyme converts glucose-6-phosphate into glucose-1-phosphate in the 2nd step of glycogenesis?

A

Phosphoglucomutase

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18
Q

Which enzyme converts glucose-1-phosphate into UDP-glucose in the 3rd step of glycogenesis?

A

G1P uridylyltransferase

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19
Q

What is the equation for the 3rd step of glycogenesis?

A

Glucose-1-phosphate + UTP + H2O —> UDP-glucose + PPi

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20
Q

Which enzyme catalyses the final step of glycogenesis?

A

Glycogen synthase

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21
Q

Which enzyme is responsible for the branching of glycogen?

A

Glycogen branching enzyme

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22
Q

What are the overall equations for glycogenolysis?

A

Glycogen(n residues) + Pi —> Glucose-1-phosphate + glycogen (n-1 residues)

Glucose-1-phosphate glucose-6-phosphate

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23
Q

What enzymes are involved in the first step of glycogenolysis where glycogen goes to glucose-1-phosphate?

A

Glycogen Phosphorylase or de-branching enzyme

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24
Q

What enzyme is involved in the conversion of glucose-6-phosphate to glucose-1-phosphate?

A

Phosphoglucomutase

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25
Q

What happens to glucose-6-phosphate in glycogenolysis?

A

Muscle - glycolysis - used by energy production

Liver - glucose - released by liver into blood for use by other tissues

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26
Q

Why does glycogen stay in the muscle to be used there?

A

Muscle lacks glucose-6-phosphatase so G6P enters glycolysis for energy production

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27
Q

What is the rate limiting enzyme in glycogen synthesis?

A

Glycogen synthase

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28
Q

What is the rate limiting enzyme in glycogen degradation?

A

Glycogen phosphorylase

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29
Q

What effect does glucagon and adrenaline have on the activity of glycogen synthase?

A

Decreases the activity

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30
Q

What effect does glucagon and adrenaline have on the activity of glycogen phosphorylase?

A

Increases the activity

31
Q

What effect does insulin have on the activity of glycogen synthase?

A

Increases the activity

32
Q

What effect does insulin have on the activity of glycogen phosphorylase?

A

Decreases the activity

33
Q

Why does glucagon have no effect on muscle glycogen stores?

A

Muscle cells do not have glucagon receptors

34
Q

What is an allosteric activator of muscle glycogen phosphorylase?

A

AMP

35
Q

What do glycogen storage diseases arise from?

A

Deficiency or dysfunction of enzymes of glycogen metabolism

36
Q

What are some examples of glycogen storage diseases?

A

McArdle disease, von Gierke’s disease

37
Q

What is the enzyme deficient is von Gierke’s disease?

A

Glucose 6-phosphatase

38
Q

What is often seen in von Gierke’s disease?

A

Enlarged liver

39
Q

What enzyme is deficient in McArdle disease?

A

Muscle glycogen phosphorylase

40
Q

At how many hours of fasting do liver glycogen stores start to deplete?

A

After 8 hours

41
Q

Where does gluconeogenesis occur?

A

Liver and to lesser extent in kidney cortex

42
Q

What are the 3 major precursors to glucose for gluconeogenesis?

A

Lactate, glycerol, amino acids (mainly alanine)

43
Q

What is the cori cycle?

A

Metabolic process in which lactate produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is metabolised back to lactate

44
Q

True or False:

Acetyl-CoA can be converted into pyruvate

A

False

Acetyl-CoA cannot be converted into pyruvate as the pyruvate dehydrogenase reaction is irreversible so there is no net synthesis of glucose from acetyl coA

45
Q

What are the key enzymes in gluconeogenesis?

A

1) Phosphoenolpyruvate carboxykinase (PEPCK)
2) Fructose 1,6 bisphosphatase
3) Glucose-6-phosphatase

46
Q

What does PEPCK convert?

A

Converts oxaloacetate into phosphoenolpyruvate and CO2

47
Q

What does Fructose 1,6-bisphosphatase convert?

A

Fructose 1,6 bisphosphate into Fructose-6-phosphate

48
Q

What does glucose-6-phosphatase convert?

A

Glucose-6-phosphate into glucose

49
Q

Which are the two key enzymes regulated by hormones that regulate gluconeogenesis?

A

PEPCK and Fructose 1,6-bisphosphatase

50
Q

What is the effect of glucagon and cortisol on PEPCK?

A

Increases the amount so stimulates gluconeogenesis

51
Q

What is the effect of glucagon and cortisol on Fructose 1,6-bisphosphatase?

A

Increases amount and activity so stimulates gluconeogenesis

52
Q

What is the effect of insulin on PEPCK?

A

Decreases the amount so inhibits gluconeogenesis

53
Q

What is the effect of insulin on Fructose 1,6-bisphosphatase?

A

Decreases amount and activity so inhibits gluconeogenesis

54
Q

After feeding, when does gluconeogenesis occur?

A

8-10 hours after

55
Q

What are lipids stored as?

A

Triglycerides

56
Q

Describe adipocytes

A

Contain large lipid droplet, cytoplasm and organelles pushed to edge

57
Q

How much can adipocytes increase in size on weight gain before dividing and increasing total number of fat cells?

A

About fourfold

58
Q

What transports dietary fat?

A

Chylomicrons

59
Q

Where do chylomicrons travelling in the lymph enter the blood?

A

Left subclavian vein

60
Q

Which enzyme produces malonyl-coA from acetyl-coA?

A

Acetyl-CoA carboxylase

61
Q

How many carbons does malonyl-CoA have?

A

3

62
Q

What builds fatty acids by sequential addition of 2 carbons provided by malonyl-CoA and what is required?

A

Fatty acid synthase complex

Requires ATP and NADPH

63
Q

What increases the activity of acetyl-coA carboxylase?

A

Insulin and citrate

64
Q

What decreases the activity of acetyl-coA carboxylase?

A

Glucagon, adrenaline and AMP

65
Q

What is produced when malate is converted to pyruvate?

A

NADPH

66
Q

How is malonyl coA produced for use with fatty acid synthase complex to produce fatty acids?

A

Citrate from TCA forms acetyl coA which is acted upon by acetyl-coA carboxylase to make malonyl coA

67
Q

What does VLDL stand for?

A

Very low density lipoproteins

68
Q

Where does fatty acid synthesis occur within the cell?

A

Cytoplasm (whereas fatty acid oxidation occurs in mitochondria)

69
Q

Is fatty acid synthesis an oxidative or reductive process?

A

Reductive - requires NADPH

70
Q

What is fatty acid synthesis regulated by?

A

Activity of acetyl-coA carboxylase

71
Q

What stimulates fatty acid synthesis?

A

Insulin

72
Q

What inhibits fatty acid synthesis?

A

Glucagon and adrenaline

73
Q

What effect does glucagon and adrenaline have on hormone sensitive lipase (HSL)?

A

Leads to phosphorylation and activation of HSL

74
Q

What effect does insulin have on hormone sensitive lipase (HSL)?

A

De-phosphorylation and inhibition of HSL

ESA2 - Metabolism, Endocrinology and Haematology (19 decks)

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