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POM 3 Haematology > 3.2 Haemoglobin > Flashcards

3.2 Haemoglobin Flashcards

1
Q

What protein is involved in the transport of oxygen from the lungs to the tissues?

A

Haemoglobin

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2
Q

Describe the structure of haemoglobin?

A
  • Consists of 4 globin chains
  • Each globin chain contains a haem group
  • Each haem group is has a central ferrous iron atom (fe2+) surrounded by a porphyrin ring
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3
Q

What four chains are HbA molecules made up from?

A

2 alpha chains and 2 beta chains

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4
Q

What two chain type is fetal haemoglobin made from?

A

2 alpha chains and 2 gamma chains

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5
Q

What is meant by the positive cooperative binding which oxygen displays?

A

As oxygen binds to Hb, a conformational change occurs in the other subunits

This increases the affinity of the other haem groups for oxygen, resulting in the sigmoidal O2 dissociation curve

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6
Q

How is the oxygen affinity different in fetal haemoglobin compared with adult haemglobin?

A

The oxygen affinity is higher

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7
Q

How does HbF have a higher oxygen affinity than HbA?

A

A single AA substitution results in reduced affinity for 2,3-DPG and therefore a higher oxygen affinity

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8
Q

Why is it essential that fetal haemaglobin has a high affinity for oxygen?

A

This means at very low concentrations of oxygen, which the placenta has, HbF can still readily bind the oxygen which the HbA is offloading

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9
Q

Why can myoglobin not display positive cooperativity?

A

It only has one oxygen binding site

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10
Q

What is the p50 value for myoglobin and haemaglobin respectively?

A

Myoglobin = 2
Hb = 26

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11
Q

Where is myoglobin found?

A

Predominantly in the muscle cells

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12
Q

Why is myoglobin useful?

A

It is a store of oxygen in muscles

It has a high oxygen affinity and only releases the oxygen it stores at low oxygen concentration

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13
Q

A right shift in the oxygen dissociation curve is associated with what change?

A

A decrease in the oxygen affinity

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14
Q

A left shift in the oxygen dissociation curve is associated with what change?

A

An increase in the oxygen affinity

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15
Q

What factors could cause an increase in the oxygen affinity (left shift)?

A

Decreased CO2, decreased 2,3-DPG, increased pH

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16
Q

What factors could cause a decrease in the oxygen affinity (right shift)?

A

Increased CO2, decreased pH, increased 2,3-DPG, increased temperature

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17
Q

Describe how a left shift in the oxygen dissociation curve results in an increase in the affinity for oxygen?

A

When the curve shifts left, the saturation of Hb is higher at the same partial pressure of oxygen

This is due to increased oxygen affinity thus Hb is less likely to release oxygen, hence being more saturated

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18
Q

How is 2,3-DPG produced?

A

Leubering–Rapoport shunt

19
Q

How does 2,3-DPG affect Hb?

A

It stabilises the structure and reduces the affinity for oxygen

20
Q

What is the p50 value?

A

The value at which 50% of the oxygen molecules have bound

21
Q

Why is Hb described as a tetramer?

A

because it has 4 globin chains

22
Q

Describe what is meant by globin gene switching, and when does it occur?

A

The switch from gamma to beta chains, producing HbA from HbF

Occurs at birth

23
Q

What is carboxyhaemaglobin?

A

Molecule formed when carbon monoxide binds to Fe2+ in haemoglobin

24
Q

How does the affinity of Hb for CO differ from that of oxygen and what does this mean?

A

Much higher affinity for CO than O2

Thus CO can outcompete O2 for the 4 Hb binding sites

25
Q

What is MetHb?

A

Methaemoglobin

26
Q

How is MetHb generated?

A

Formed when ferrous (2+) iron is oxidised to the ferric (3+) state, impairing O2 binding

27
Q

What is present if your blood has a blueish/chocolate colour?

A

Methaemoglobin

28
Q

What enzyme is used to reduce methaemoglobin back to haemaglobin?

A

Methaemoglobin reductase

29
Q

What effect does MetHb have on oxygen and what does this cause?

A

MetHb can carry oxygen but cannot release it to the tissues, leading to hypoxia

30
Q

What is methaemoglobinaemia?

A

Disorder where abnormal amounts of MetHb are produced

31
Q

What causes methaemoglobinaemia?

A

Deficiency in methaemoglobin reductase or production of mutant haemoglobin M resistant to reduction

32
Q

How can methaemoglobinaemia be acquired?

A

Hereditary

Exposure to aniline dyes, nitrates, benzene, benzocaine

33
Q

What does the absorbance spectrum look like for oxy-haemoglobin?

A

There are two peaks, with one at 540

34
Q

What is the ideal wavelength to set the haemoglobin absorbance spectrum at?

A

540 nm

35
Q

When is spectrophotometry used clinically?

A

To check the respiratory status of newborn babies by following changes in binding by Hb

36
Q

What is pulse oximetry?

A

Non-invasive way of measuring oxygen saturation levels

37
Q

Which is more negatively charged, HbA or HbS?

A

HbA is more negative

38
Q

Why is HbS not as negatively charged as HbA?

A

A single point mutation occurs in the Beta chain of HbS

Glutamate is replaced by valine

39
Q

What effect does the single base substitution forming HbS have?

A

Substitution of hydrophilic, negatively charged glutamate to hydrophobic, positively charged valine

40
Q

In gel electrohoresis, how can HbS be differentiated from HbA?

A

HbS will be less negative and therefore not move as far towards the positive electrode (anode) as HbA will

41
Q

How does chromatography on cellulose separate proteins?

A

On the basis of their charge

42
Q

What is the role of the Luebering–Rapoport shunt in red blood cells?

A

To generate 2,3-DPG which facilitates oxygen release at tissue sites by stabilising Hb via allosteric binding

43
Q

How does HbS compensate for its lower Hb levels than HbA?

A

HbS has a lower affinity for O2, thus O2 is liberated to tissues at a lower partial pressure

POM 3 Haematology (10 decks)

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