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Biochemistry > Agents that affect oxygen binding > Flashcards

Agents that affect oxygen binding Flashcards

1
Q

What kind of protein is haemoglobin?

A

Allosteric protein that displays cooperativity in oxygen binding and release

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2
Q

Is the binding of oxygen by myoglobin cooperative?

A

No because it is a monomer (only one subunit)

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3
Q

What is oxygen binding measured as a function of?

A

The partial pressure of oxygen

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4
Q

What is the iron bound to in haemoglobin?

A

4 nitrogens

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5
Q

What is the 5th coordination site of iron occupied by?

A

Imidazole ring of a histidine (proximal histidine)

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6
Q

What binds to the 6th coordination site of iron?

A

Oxygen

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7
Q

What happens to the iron when oxygen binds to it?

A

It moves into the plane of the protoporphyrin ring which pushes amino acids to different position

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8
Q

What stabilises the bound oxygen?

A

The distal histadine

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9
Q

Why can fMRI distinguish the relative amounts of oxy- and deoxyhemoglobin?

A

Because the magnetic properties of the heme iron changes when it moves into the plane of the protoporphyrin ring

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10
Q

What is the concept called which makes heme have higher affinity for oxygen once one is bound?

A

Cooperativity

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11
Q

What kind of oxygen binding curve does myoglobin display?

A

Hyperbolic

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12
Q

What kind of oxygen binding curve does haemoglobin display?

A

Sigmoid curve which indicates that O2 binding and release is cooperative

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13
Q

When partial pressure of oxygen decreases, what happens to the affinity?

A

It also decreases

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14
Q

Is haemoglobin exposed to superoxide ions?

A

No

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15
Q

Why is it critical that oxygen is only released in the O2 and not superoxide state?

A

Superoxide is very reactive and will bind and harm other molecules
Iron ion would be left in the ferric (Fe3+) state, preventing additional oxygen binding (Myoglobin in this state is called metmyoglobin)

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16
Q

What is myoglobin called when iron ion is left in the ferric state (Fe3+), preventing additional oxygen binding?

A

Metmyoglobin

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17
Q

What feature of myoglobin help prevent superoxide release?

A

Distal histidine which donate a hydrogen bond to the oxygen molecule

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18
Q

What will exercise do to the partial pressure of oxygen in a tissue?

A

Oxygen will deplete so the partial pressure goes down in the tissue

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19
Q

2 models that describe how haemoglobin goes from T state to R state?

A

Concerted model
Sequential model

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20
Q

Which model is most likely? Concerted or sequential

A

Both, they most likely both happen

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21
Q

Which interface is the structural changes at the heme groups transmitted to?

A

Alpha1 Beta2
Alpha2 Beta1

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22
Q

Where do allosteric effector bind on haemoglobin?

A

At a site separate from the active site

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23
Q

What is the activity of an allosteric protein regulated by?

A

Allosteric effectors

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24
Q

What is oxygen? A homotropic of heterotrophic allostery?

A

Homotropic allosteric modulator because it is itself the ligand, not only a molecule that modifies the structure of haemoglobin but also the molecule that binds haemoglobin

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25
Q

What is a homotropic allosteric effector?

A

A molecule that affects its own binding to the protein (at other site)
Like how binding of O2 increases the affinity for binding on other side of Hb

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26
Q

What os a heterotropic allosteric effector?

A

When the allosteric effector is different from the ligand whose binding is altered
Like the effect og H+ on the P50 for oxygen binding

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27
Q

What shift in the O2 binding curve do interactions with homotropic and heterotrophic allosteric effectors lead to?

A

Horizontal shifts

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28
Q

Examples of homotropic allosteric effectors

A

CO2
2,3-bisphosphoglycerate
H+

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29
Q

Do heterotrophic allosteric effects increase or decrease the affinity for O2?

A

Decrease (thus deliver more oxygen to the tissue)

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30
Q

What is 2,3-bisphosphoglycerate?

A

A byproduct of glycolysis
Negatively charged small molecule which binds to the T-state and stabilises it by binding in positively charged pocket at the interface of each subunits (between the beta subunits)

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31
Q

2 subunits does foetal haemoglobin not have?

A

The beta subunits

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32
Q

2 subunits does foeatal haemoglobin have?

A

The gamma subunits

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33
Q

What does the gamma subunit defer from the beta subunit?

A

1 amino acid

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34
Q

Why does 2,3-bisphosphoglycerate not bind to foetal haemoglobin?

A

Because it has gamma subunits instead of beta subunits so no positively charged pocket

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35
Q

At the same concentrations of 2,3-bisphosphoglycerate, which has a higher affinity for oxygen, maternal or foetal haemoglobin?

A

Foetal

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36
Q

What is the role of distal histidine regularly?

A

Increases the affinity for oxygen by making the space better fit for oxygen by bending the angle of binding to fit oxygen’s angle

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37
Q

Why is CO so toxic?

A

Because it saturates the haemoglobin so oxygen can’t bind and you die. It does so very quickly

38
Q

What does distal histidine do?

A

Keeps oxygen (and CO) at an angle

39
Q

What can destabilise the affinity for CO?

A

The distal histidine, but CO still binds better

40
Q

What does CO act as when bound to heme?

A

An irreversible ligand

41
Q

Is the affinity for O2 greater than CO?

A

No the affinity for CO is 2000 times greater

42
Q

What is hypoxia?

A

Low availability of oxygen in a tissuwe

43
Q

How does temperature effect the affinity for oxygen?

A

The higher the temperature the less affinity for oxygen

44
Q

Examples of hemoglobinopathies?

A

Sickle cell disease
Thalassemia

45
Q

What are hemoglobinopathies?

A

Genetic disorder affecting the production or structure of haemoglobin molecule

46
Q

What gives sickle cell diseased RBC their sickle shape?

A

The fibers of haemoglobin being misshaped

47
Q

What is thalassemia caused by?

A

An imbalanced production of haemoglobin chains

48
Q

What is alpha-thalassemia?

A

When there is not enough alpha chains

49
Q

What can cytoglobin protect against?

A

Hypoxia

50
Q

What can glycated haemoglobin tell you about glucose levels?

A

Levels from the past 3 months

51
Q

Is the binding of oxygen in myoglobin cooperative?

A

No

52
Q

What forms the 5th coordination bond with iron?

A

Proximal histidine

53
Q

What forms the 6th coordination bond with iron?

A

Oxygen

54
Q

What happens to the magnetic properties of the heme iron when it moves into the plane of the protoporphyrin?

A

It changes

55
Q

Why can fMRI distinguish the relative amounts oxygenated and deoxygenated haemoglobin?

A

Because the properties of the heme iron changes

56
Q

2 reasons why it is critical that oxygen is released only in the oxygen and not the superoxide state

A

Superoxide is very reactive and can harm other cellular molecules
The iron would be left in the ferric state, preventing it from binding additional oxygen

57
Q

What are the main factors that affect the binding of oxygen to haemoglobin?

A

pH
CO2
2,3biphosphoglicerate

58
Q

Which way does the saturation curve shift when an allosteric effector is added?

A

To the right

59
Q

What does the shift to the right of the saturation curve indicate?

A

Decreased affinity for oxygen

60
Q

Which way does the saturation curve shift when an allosteric effector is removed?

A

To the left

61
Q

Does a decrease in pH increase or decrease the affinity for oxygen?

A

Decrease

62
Q

Is 2,3-bisphosphoglycerate a negative or positive regulator of haemoglobin?

A

Negative

63
Q

What is 2,3-bisphosphoglycerate produced from?

A

An intermediate in glycolysis

64
Q

Where on the haemoglobin does 2,3-bisphosphoglycerate bind?

A

The positively charged central cavity

65
Q

Why does the 2,3-bisphosphoglycerate bind to the positively charged cavity?

A

Because it is negatively charged because of the phosphate

66
Q

In which state of haemoglobin does 2,3-bisphosphoglycerate bind better?

A

T state because it is closed in R state

67
Q

What happens to oxygen delivery at high altitudes?

A

It declines by 1/4th to a max of 30%

68
Q

What does 2,3-bisphosphoglycerate facilitate?

A

Unloading of oxygen in tissues

69
Q

Where is the 2,3-bisphosphoglycerate in competition with oxygen for the binding site?

A

On the beta subunit

70
Q

Does fetal haemoglobin have a high or low 2,3-bisphosphoglycerate affinity?

A

Low

71
Q

What is the Bohr effect?

A

Carbon dioxide and H+ stimulating the release of oxygen

72
Q

Example of something that can induce the Bohr effect?

A

Lowering the pH as it decreases the affinity for oxygen

73
Q

Which amino acid is a big contributor to the Bohr effect?

A

His146 of the beta subunit

74
Q

Which enzyme catalyses the reaction of Oxygen binding by haemoglobin?

A

Carbonic anhydrase

75
Q

What is carbonic anhydrase important to keep constant?

A

pH

76
Q

How does CO2 effect eh affinity of haemoglobin to oxygen?

A

It decreases it

77
Q

2 signals to to haemoglobin that we need more oxygen

A

Release of hydrogen and 2,3-DPG

78
Q

In what form is 15-20% of CO2 exported?

A

Carbamate

79
Q

What does the formation of carbamate yield?

A

A proton and saltbridges

80
Q

How does the formation of carbamate contribute to the Bohr effect?

A

By yielding a proton

81
Q

How does the formation of carbamate stabilise the T state?

A

By forming additional salt bridges

82
Q

Which binds better, carbon monoxide or oxygen?

A

Carbon monoxide

83
Q

In what shape does carbon monoxide bind? Linear or bent?

A

Linear

84
Q

How does temperature affect the oxygen affinity?

A

Higher temperature means lower oxygen

85
Q

What are hemoglobinopathies?

A

Haemoglobin mutants

86
Q

What mutation causes sickle cell disease?

A

Substitution of Valine for glutamate

87
Q

When is sickle cell anaemia fetal?

A

When both alleles of the beta chain are mutated

88
Q

What does an individual with sickle cell disease present clinically?

A

Intermittent episodes of haemolytic anaemia resulting from chronic lysis of red cells and painful vasoocclusive crisis

89
Q

What kind of trait is sickle cell disease?

A

Heterozygous recessive

90
Q

What does it mean that haemoglobin can be glyciated?

A

That it can bind to glucose

Biochemistry (28 decks)

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