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Z OLD Molecules, Genes and Disease > Haemoglobin and Myoglobin > Flashcards

Haemoglobin and Myoglobin Flashcards

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Organic Chemistry 101 flashcards
1
Q

Why doesn’t oxygen dissolve well in aq or water solutions?

A

Because it’s not a very polar molecule

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2
Q

What is the result of oxygens inability to dissolve well?

A

It cannot travel in the bloodstream

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3
Q

What happens as organisms get larger?

A

Need to find an effective mechanism of transporting oxygen

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4
Q

What is present in muscle?

A

Myoglobin

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5
Q

What does myoglobin do?

A

Accepts oxygen from haemoglobin

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6
Q

What does oxygen bind to?

A

Haem groups (not amino acids directly)

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7
Q

What does haem consist of?

A

Protoporphyrin ring, and Fe atom bound to 4 N atoms of ring

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8
Q

What part of the haem group is important?

A

Only the Fe, the rest just holds it in the ring

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9
Q

How many additional bonds can Fe 2+ make?

A

2- one on either side of the plane

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10
Q

What is Fe 2+ covalently bonded to in haemoglobin?

A

The protein

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11
Q

What is the result of Fe 2+ being covalently bonded to protein in haemoglobin?

A

Only 1 molecule of oxygen binds

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12
Q

How many molecules of oxygen bind in myoglobin?

A

1

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13
Q

How is the Fe atom bound to the protein?

A

Via a histidine residue on the other side of the ring

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14
Q

What is the histidine residue that the Fe atom binds to known as?

A

The proximal histidine

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15
Q

How many amino acids are there in myoglobin?

A

153

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16
Q

Is myoglobin compact or loose?

A

Compact

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17
Q

What % of myoglobin is made up of α-helixes?

A

75%

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18
Q

In myoglobin, which histidine is linked to the Fe atom?

A

His93

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19
Q

Where is the Fe in deoxymyoglobin?

A

Slightly below the plane of the ring

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20
Q

What does oxygen binding cause in myoglobin?

A

Movement of the Fe upwards, into the plane of the ring

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21
Q

What does the movement of Fe upwards in myoglobin cause?

A

Movement of His18, and a small change in overall protein conformation

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22
Q

Is the change in protein confirmation on oxygen binding important?

A

No

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23
Q

What relationship does oxygen binding to myoglobin show to oxygen concentration?

A

Hyperbolic

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24
Q

What can we tell from the hyperbolic binding curve of myoglobin binding and concentration of oxygen?

A

Myoglobin has save affinity to oxygen all the way through

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25
Q

What binding relationship does haemoglobin show against concentration of oxygen?

A

Sigmoidal

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26
Q

What is haemoglobin affinity for oxygen at low partial pressures?

A

Low

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27
Q

What happens to haemoglobins affinity for oxygen as partial pressure increases?

A

It increases

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28
Q

How many different types of polypeptide chain are there in haemoglobin?

A

2

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29
Q

What are the two different polypeptide chains in haemoglobin?

A
  • α

- ß

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30
Q

How many amino acids are there in the α chain of haemoglobin?

A

141

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31
Q

How many amino acids are there in the ß chain of haemoglobin?

A

146

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32
Q

What conformation is adult haemoglobin in?

A

α 2 ß 2 tetramer

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33
Q

What is meant by aα 2 ß 2 tetramer?

A

There are 2 α chains and 2 ß chains

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34
Q

What does each polypeptide chain in haemoglobin have?

A

An essential haem prosthetic group

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35
Q

In what states does deoxyhaemoglobin exist?

A
  • Low affinity T state

- High affinity R state

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36
Q

What does oxygen binding promote?

A

Stabilisation of the R state

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37
Q

What is the difference between the T and the R state?

A

From the T to the R state, the molecule has twisted round ~18º, which means histidines and negatively charged groups make interactions, which holds the molecule in high affinity. The haem group is now more exposed

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38
Q

What is the result of the haem group being more exposed?

A

It can bind to oxygen more easily

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39
Q

What happens when oxygen binds to haemoglobin?

A

The ferrous atom is pulled into the centre

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40
Q

What is the result of the pulling of the ferrous atom into the centre?

A

It pulls the entire sub unit, which has an effect on the entire molecule

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41
Q

What is the effect on the molecule of the movement of the ferrous ion on binding with oxygen?

A

It moves some amino acids, promoting being pulled into the high affinity state

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42
Q

What is meant by ‘co-operative binding’?

A

When binding of one oxygen molecule promotes the binding of subsequent oxygen molecules

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43
Q

What does the sigmoidal binding curve of haemoglobin mean?

A

That oxygen can be efficiently carried from the lungs to the tissues

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44
Q

Is it easy or hard for haemoglobin to take its first oxygen?

A

Hard

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45
Q

What happens once 1 oxygen molecule is binded?

A

Conformation changes to make subsequent binding easier

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46
Q

Is the partial pressure of oxygen in the lungs high or low?

A

High

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47
Q

What does the high p.p of oxygen in the lungs promote?

A

Binding of oxygen to haemoglobin molecules

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48
Q

Is the partial pressure of oxygen in the tissues high or low?

A

Low

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49
Q

Why is the partial pressure of oxygen in the tissues low?

A

Because other tissues have used the oxygen in the tissues to respire

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50
Q

What does haemoglobin need to do at the tissues?

A

Change its affinity

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51
Q

What is the ability of oxygen to change it’s affinity known as?

A

Co-operativity

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52
Q

What is the advantage of co-operativity?

A

More oxygen can be transported, as more is picked up at the lungs and then more released in tissues

53
Q

What molecules are used to regulate oxygen binding?

A
  • 2,3-bisphosphoglycerate (2,3-BPG)

- CO 2 and H +

54
Q

What is the problem with oxygen under normal conditions?

A

It’s too effective to work

55
Q

How is haemoglobins affinity to oxygen different without 2,3-BPG?

A

It’s higher

56
Q

What does 2,3-BPG do to the binding curve of haemoglobin?

A

Moves it to the right

57
Q

What does 2,3-BPG act as?

A

An allosteric inhibitor

58
Q

Where does 2,3-BPG come from?

A

It’s a byproduct of glycolysis

59
Q

At what concentration is 2,3-BPG present in RBC’s?

A

~5mM

60
Q

How much 2,3-BPG binds per haemoglobin tetramer?

A

1

61
Q

How does 2,3-BPG bind to haemoglobin?

A

The negatively charged phosphate binds to positively charged amino acid in ß sub units

62
Q

How does 2,3-BPG concentration change at high altitudes?

A

It increases

63
Q

Why does 2,3-BPG change at high altitudes?

A

To promote oxygen release at tissues

64
Q

What affect does the binding of CO 2 and H + have on haemoglobin?

A

It lowers the affinity of haemoglobin for oxygen

65
Q

What is the effect CO 2 and H + has on haemoglobin known as?

A

The Bohr effect

66
Q

What happens when CO 2 dissolves in water?

A

It gives carbonic acid

67
Q

What happens to carbonic acid in solution?

A

It dissociates to give H +

68
Q

What do metabolically active tissues produce?

A

Large amounts of H + and CO 2 , and acidic metabolic intermediates

69
Q

What does the Bohr effect ensure?

A

Delivery of oxygen coupled to demand

70
Q

How does the Bohr effect ensure delivery of oxygen is coupled to demand?

A

If tissues are working hard, they make more CO 2 and acidic intermediates, so lower affinity, so oxygen given up more.
Hard working tissues require more oxygen

71
Q

When is CO produced?

A

In the incomplete combustion of gas

72
Q

Why is CO a poison?

A

Because it combines with ferromyoglobin and ferrohaemoglobin, blocking oxygen transport

73
Q

How does the binding of CO to haemoglobin differ to that of oxygen?

A

CO binds 250x more readily

74
Q

What does CO act as?

A

A competitive inhibitor

75
Q

What happens once CO has binded?

A

It doesn’t come off under normal physiological circumstances

76
Q

When is CO poisoning fatal?

A

When COHb >50%

77
Q

What happens at COHb >50%?

A

Makes haemoglobin change confirmation so theres a higher affinity in unaffected subunits

78
Q

Why is the increased affinity caused by CO fatal?

A

It means that oxygen will be taken up at the lungs, but not released at the tissues

79
Q

What is the treatment for CO poisioning?

A
  • Hyperbaric chamber

- In extreme cases, blood transfusions

80
Q

How does a hyperbaric chamber work?

A

It increases oxygen concentration, and so increasing oxygen saturation in the lungs

81
Q

What are the 3 types of normal adult haemoglobins?

A
  • HbA (α 2 ß 2 )
  • HbF (α 2 γ 2 )
  • HbA 2 (α 2 δ 2 )
82
Q

How do different types of haemoglobin differ from one another?

A

The ß sub-unit is replaced with something else

83
Q

What % of haemoglobin is HbA?

A

90%

84
Q

What % of haemoglobin is HbF?

A
85
Q

What % of haemoglobin is HbA 2 ?

A

2-5%

86
Q

What does glycosylation of HbA form?

A

HbA 1C

87
Q

When is expression of different α- and ß- globin genes regulated?

A

During development

88
Q

What is the result of gene expression?

A

Different genes are expressed at different points of life

89
Q

Where are the globin genes that express different globin sub-units?

A

On 2 different locations on 2 different chromosomes

  • On chromosome 16, 2 α like genes
  • On chromosome 11, 2 ß sub units
90
Q

What is HbF?

A

Fetal haemoglobin

91
Q

Where is foetal haemoglobin the major type?

A

In foetal blood

92
Q

How does HbF differ from HbA?

A

Higher binding affinity

93
Q

What does the higher binding affinity of HbF allow for?

A

Transfer of oxygen to the foetal blood supply from the mothers

94
Q

What must be the case for transfer of oxygen from maternal to foetal blood?

A

The foetal haemoglobin must be of higher affinity

95
Q

What is sickle cell haemoglobin known as?

A

HbS

96
Q

What is sickle cell anaemia a mutation of?

A

Glutamate (negative amino acid) to valine (neutral, hydrophobic) in ß globin

97
Q

Why is the mutation in HbS significant?

A

Glutamate normally sits on the surface and is happy to interact with water. If mutated, valine is hydrophobic, so haemoglobin sticks 2 ß sub units together to exclude water

98
Q

What is formed as a result of the mutation in HbS?

A

A sticky hydrophobic pocket formed by valine

99
Q

What does the sticky hydrophobic pocket in HbS allow?

A

Deoxygenated HbS to polymerise

100
Q

What are sickled cells more prone to?

A

Lyse

101
Q

What does the lysis of blood cells lead to?

A

Anaemia

102
Q

How to HbS cells differ from normal cells in terms of flexibility?

A

They are more rigid

103
Q

What is the result of the rigidity of HbS cells?

A

They block microvasculature

104
Q

What is produced when sickled cells stick together?

A

Abnormal chains

105
Q

Do sickled cells work as oxygen transporters?

A

No

106
Q

What happens to the sickled cells chains?

A

They clump together and bind to the cell membranes

107
Q

What is the result of sickled cells binding to cell membranes?

A

They make the membranes much more rigid

108
Q

What property to RBC’s usually have?

A

They’re usually squashy

109
Q

What is the importance of the squashiness of RBC’s?

A

They can fit through capillaries

110
Q

What is the result of sickled cells not having the squashy quality of normal RBC’s?

A

When they try and get through capillaries, they either block of lyse

111
Q

What happens when sickled cells block vessels?

A

Painful symptoms

112
Q

What are thalassaemias?

A

A group of genetic disorders that result from an imbalance in α- and ß- globin chains

113
Q

What is normally the ratio between α and ß globin chains?

A

01:01

114
Q

How many an imbalance between α and ß globin chains arise?

A

NAME?

115
Q

What are ß-thalassemias?

A

When there is decreased/absent ß-globin chain production

116
Q

What is the problem with ß-thalassemias?

A

α-chains are unable to form stable tetramers

117
Q

What happens if not enough ß sub units are being made?

A

Excess α can precipitate out

118
Q

Can a 4 α sun unit transport oxygen?

A

No

119
Q

When do symptoms of ß thalassaemias appear?

A

After birth

120
Q

What do the different forms of ß-thalassaemias depend on?

A

How many forms are absent

121
Q

What is thalassaemia minor?

A

When one form is missing/mutated

122
Q

What is thalassaemia major?

A

When both forms are missing/mutated

123
Q

What is HbBarts?

A

When haemoglobin is formed purely fromγ sub-units

124
Q

What are α-thalassemias?

A

When there is decreased/absent α-globin chain production, resulting in excess ß sub units

125
Q

What are the levels of severity of α thalassaemias due to?

A

Multiple copies of the α chain being present

126
Q

Can ß chains form stable tetramers?

A

Yes

127
Q

How do ß chain tetramers differ from normal ones?

A

They have a higher affinity

128
Q

What is the problem with the higher affinity of ß chain tetramers?

A

They pick up oxygen, but won’t release it

129
Q

When is the onsets of α thalassaemias?

A

Before birth

Z OLD Molecules, Genes and Disease (14 decks)

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