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Biochem Take 2. > The Hexose Monophosphate Pathway. > Flashcards

The Hexose Monophosphate Pathway. Flashcards

1
Q

What is the HMP pathway used for?

A

It is an alternative pathway for the oxidation of glucose.

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2
Q

What other names is the HMP pathway known as?

A

HMP pathway.

Hexose monophosphate shunt.

6-phosphogluconate pathway.

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3
Q

What are the products of the HMP pathway?

A

2 molecules of NADPH.

3 pentose phosphates.

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4
Q

What are the 3 pentose phosphates that are formed in the HMP pathway?

A

Ribose 5-phosphate.

Ribulose 5-phosphate.

Xylulose 5-phosphate.

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5
Q

What is ribulose 5-phosphate used for?

A

DNA and RNA synthesis.

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6
Q

What can NADPH be used form?

A

It can help form fatty acids and steroid hormones.

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7
Q

What will NADH help to form that will de-toxify the cell?

A

Reduced glutathione.

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8
Q

Where does the HMP pathway take place?

A

In the cytoplasm.

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9
Q

Where are all the enzymes for the HMP located?

A

In the cytoplasm.

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10
Q

What enzymes are used in the HMP?

A

Transaldolase.

Transketolase.

Several dehydrogenases.

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11
Q

What are the 2 phases that occur in the HMP pathway?

A

The oxidative phase.

The non oxidative phase.

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12
Q

What goes into the oxidative phase of the HMP?

A

Glucose 6-phosphate.

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13
Q

What comes out of the oxidative phase of the HMP?

A

Ribulose 5-phosphate.

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14
Q

What goes into the non-oxidative phase of the HMP?

A

Ribulose 5-phosphate.

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15
Q

What comes out of the non-oxidative phase of the HMP?

A

Ribose 5-phosphate.

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16
Q

What can ribulose 5-phosphate be used to form?

A

Ribose 5-phosphate.

It can be interconverted to carbohydrates and glycolytic/gluconeogenic precursors.

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17
Q

Are all the products from ribulose 5-phosphate formed in non oxidative reactions?

A

Yes.

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18
Q

Is any energy used in the HMP pathway?

A

No ATP or NADH are used in the HMP pathway.

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19
Q

The NADPH that is formed in the liver, adipose tissue, the lactating mammary gland will be used to synthesise what?

A

Fatty acids.

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20
Q

The NADPH that is formed in the adrenal cortex, ovaries, testes and the placenta will be used to synthesise what?

A

Steroid hormones and in hydroxylation reactions.

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21
Q

The NADPH that is formed in the erythrocytes will be used for what?

A

For the reduction of glutathione.

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22
Q

The NADPH that is formed in the white blood cells and

in macrophages will be used for what?

A

Phagocytose bacteria.

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23
Q

The NADPH that is formed in the thyroid will be used to synthesise what?

A

Thyroid hormones.

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24
Q

What are the 2 phases in the HMP pathway?

A

The oxidative phase and the non oxidative phase.

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25
Q

In what phase of the HMP are all of the reactions irreversible?

A

The oxidative phase.

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26
Q

In what phase of the HMP is NADPH formed?

A

The oxidative phase.

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27
Q

In what phase of the HMP are all of the enzymes dehydrogenases?

A

The oxidative phase.

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28
Q

What is the regulatory enzyme in the HMP pathway?

A

G-6-Phospahte dehydrogenase.

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29
Q

What happens in step 1 of the oxidative phase of the HMP pathway?

A

Glucose 6-phosphate is converted to 6-phosphogluconate.

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30
Q

What energy is created in step 1 of the oxidative phase of the HMP pathway?

A

NADPH.

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31
Q

What 2 enzymes are used in step 1 of the oxidative phase of the HMP pathway?

A

Glucose 6-phosphate dehydrogenase.

Phosphoglucolactone hydrolase (lactonase).

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32
Q

Is step 1 of the oxidative phase a regulatory step of the HMP pathway?

A

Yes.

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33
Q

What happens in step 2 of the oxidative phase of the HMP pathway?

A

A carbon is removed as CO2 from 6-phosphogluconate to form ribulose 5-phosphate.

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34
Q

What is a decarboxylation reaction?

A

When a C is removed from a molecule.

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35
Q

What energy is created in step 2 of the HMP pathway?

A

1 NADPH.

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36
Q

What enzyme is used in step 2 of the oxidative phase of the HMP pathway?

A

Phosphogluconate dehydrogenase.

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37
Q

Does phosphogluconate dehydrogenase require any coenzymes?

A

NADP+.

Mg2+.

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38
Q

What will activate glucose 6-phosphate dehydrogenase.?

A

Insulin.

39
Q

What will stimulate glucose 6-phosphate dehydrogenase.?

A

NADP+.

40
Q

What will inhibit glucose 6-phosphate dehydrogenase.?

A

NADPH (product).

41
Q

Will glucose 6-phosphate dehydrogenase be activated in the well fed state or the fasting state?

A

In the well fed state as it is activated by insulin.

42
Q

In what phase of the HMP are the reactions reversible?

A

The non oxidative phase.

43
Q

In what phase of the HMP is ribose 5-phosphate formed?

A

The non oxidative phase.

44
Q

In what phase of the HMP can be used to interconvert sugars to form glycolytic and gluconeogenic intermediates?

A

The non oxidative phase.

45
Q

What phase of the HMP uses the enzymes transketolase and transaldolase?

A

The non oxidative phase.

46
Q

Which phase of the HMP relies on a series of pentose phosphate interconversions?

A

The non-oxidative phase.

47
Q

What is step 1 of the non oxidative phase of the HMP?

A

Ribulose 5-phosphate is converted to ribose 5-phosphate or to xylulose 5-phosphate.

48
Q

What enzyme converts ribulose 5-phosphate to ribose 5-phosphate?

A

Ribose 5-phosphate isomerase.

49
Q

What enzyme converts ribulose 5-phosphate to xylulose 5-phosphate?

A

Phosphopentose epimerase.

50
Q

What are the 2 products of step of the non oxidative phase of the HMP?

A

Glyceraldehyde 3-phosphate.

Fructose 6-phosphate.

51
Q

Can the products of non oxidative phase of the HMP enter any other pathways?

A

They can enter glycolysis or gluconeogenesis.

52
Q

How are glyceraldehyde 3-phosphate and fructose 6-phosphate formed in the non oxidative phase of the HMP?

A

By a series of reversible inter-conversions.

53
Q

What interconversions will transketolase carry out in the non oxidative phase of the HMP?

A

Erythrose 4-phosphate and xylulose 5 phosphate to fructose 6 phosphate and glyceraldehyde 3-phosphate.

Xylulose and riblulose to glyceraldehyde 3-phosphate and sedoheptulose 7-phosphate.

54
Q

What interconversions will transaldolase carry out in the non oxidative phase of the HMP?

A

Glyceraldehyde 3-phosphate and sedoheptulose 7-phosphate to fructose 6 phosphate and erythrose 4-phosphate.

55
Q

What co-enzymes are required by transketolase?

A

Thiamine pryophosphate (TPP).

56
Q

How many carbons does transketolase move?

A

2.

57
Q

How many carbons does transaldolase move?

A

3.

58
Q

At what step will fructose 6-phosphate enter glycolysis?

A

Step 2.

59
Q

At what step will glyceraldehyde 3-phosphate enter glycolysis?

A

Step 5.

60
Q

Are all of the interconversions that are carried out in the non oxidative phase of the HMP pathway reversible or irreversible?

A

They are all reversible.

61
Q

What are the 2 ways that cells can form NADPH?

A

The HMP pathway.

NADP+ dependent malate dehydrogenase.

62
Q

What is the only way that red blood cells can form NADPH?

A

The HMP pathway.

63
Q

What is oxidative stress in a cell?

A

When oxygen is broken down to form reactive oxygen species that can damage the cell.

64
Q

Name some reactive oxygen species?

A

O2-.

H2O2.

OH.

65
Q

How does NADPH help glutathione remove reactive oxygen species from the cell?

A

It helps glutathione reductase reduce glutathione.

Reduced glutathione can be used to convert H2O2 into H2O.

This will oxidise glutathione and it must be reduced by NADPH to carry on.

66
Q

Which form of glutathione can be used to reduce ROS?

A

Reduced glutathione.

67
Q

Which form of glutathione can not be used to reduce ROS?

A

Oxidised glutathione.

68
Q

What are some vitamins that help remove ROS?

A

Vitamin A - Carotinoids.

Vitamin C - Ascorbic acid.

Vitamin E - Tocopherols.

69
Q

What does the cytochrome P-450 monooxygenase system do?

A

They add 1 molecule of O2 to a ROS while the other is reduced to water.

The addition of O will make the ROS more soluble and it can be excreted in the urine.

70
Q

Where is the P-450 monooxygenase system particularly important?

A

In the mitochondria and the microsomal system.

71
Q

The P-450 monooxygenase system helps the body to metabolise what?

A

Drugs.

72
Q

Does NADPH play a role in the monooxygenase system particularly important?

A

Yes.

73
Q

How is NADPH used by phagocytes?

A

It helps them form an oxidative burst to kill foreign cells.

74
Q

How can a deficiency in NADPH affect the immune system?

A

A deficiency in NADPH can result in many long term infections as it cannot be used to kill the invader.

75
Q

What is chronic granulomatous disease?

A

When a deficiency in NADPH results in long term infections.

76
Q

Does the synthesis of nitric oxide require NADPH?

A

Yes.

77
Q

What coenzymes does the formation of nitric oxide require?

A

Flavin mononucleotide.

Flavin adenine di-nucleotide.

Heme.

Tetrahydrobiopterin.

78
Q

What does the body use nitric oxide for?

A

To relax smooth muscles.

To prevent platelet accumulation.

It function as a neuro transmitter in the brain.

It can react oxygen free radicals to destroy bacteria.

79
Q

NADPH can only be synthesised in RBCs by what pathway?

A

The HMP pathway.

80
Q

What are the effects of H2O2 is in the red blood cells?

A

Severe oxidative stress that can kill the red blood cell.

81
Q

How is H2O2 removed from red blood cells?

A

Reduced glutathione and glutathione peroxidase convert H2O2 to water.

82
Q

How does a lack of NADPH affect reduced glutathione and glutathione peroxidase?

A

Without NADPH, glutathione peroxidase cannot be reduced and react with more ROS.

83
Q

What can cause a build up of ROS in the RBCs?

A

Some drugs.

Fava beans.

84
Q

What would a deficiency in G6-PD-H result in?

A

Hemolysis and anaemia.

85
Q

What cells are particularly sensitive to a deficiency in G6-PD-H?

A

Red blood cells.

86
Q

What are Heinz bodies

A

Dark spots in the RBC that form due to oxidative stress.

87
Q

Why will a deficiency in G6-PD-H result in less NADPH?

A

Because it helps to catalyse the formation of NADPH.

88
Q

What would a deficiency in G6-PD-H result in in new borns?

A

Neonatal jaundice and death.

89
Q

A deficiency in G6-PDH primarily affects which populations?

A

African and Mediterranean populations.

90
Q

People who have a deficiency in G6-PDH will be immune to what diseases?

A

Malaria.

91
Q

When will a person who has a deficiency in G6-PDH show symptoms?

A

When oxidative stress occurs.

92
Q

When will individuals with a deficiency in G6-PDH be susceptible to oxidative stress?

A

When exposed to oxidative drugs or fava beans.

93
Q

What happens to red blood cells when NADPH is low?

A

Oxidative stress which will lead to lysis of red blood cells and peroxidation of membrane lipids.

Biochem Take 2. (24 decks)

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