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2.2 Haematology > Structure and Function of Haemoglobin > Flashcards

Structure and Function of Haemoglobin Flashcards

1
Q

Why do we need haemoglobin
(2)

A

O2 is a nonpolar molecule and doesn’t dissolve well in the aqueous environment of the blood

Instead of depending on our lungs and water in our blood to transport oxygen we rely on haemoglobin which enhances O2s solubility in blood x100 times

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2
Q

Hb makes up what percentage of rbcs

A

Hb constitutes about 95% of rbcs dry weight

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3
Q

When does haemoglobin synthesis begin in rbcs
(3)

A

Starts at the pro-erythroblast stage

65% of Hb synthesis occurs during nucleated stages of RBC maturation

The remaining 35% occurs during the reticulocyte stage

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4
Q

Where is haem produced in rbcs

A

Haem is produced in mitochondria and cytosol

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5
Q

Where is globin produced in rbcs

A

Globin produced in cytosol by ribosomes

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6
Q

What exactly is haemoglobin

A

A conjugated globular protein consisting of globin and four haem groups

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7
Q

What is globin

A

A tetramer of two parts of unlike globin polypeptide chains

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8
Q

What is haem

A

A protoporyphyrin ring with an iron atom in the centre

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9
Q

Describe the structure of haemoglobin
(2)

A

consists of 4 chains -> 2 alpha chains and 2 non alpha chains

Each of the 4 chains is associated with one haem group located within a hydrophobic crevice

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10
Q

What haemoglobin is found in adults
(3)

A

Between 96 and 98% of haemoglobin is haemoglobin A

Between 1.5 to 3.2% is haemoglobin A2

Between 0.5 and 0.8% is Haemoglobin F

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11
Q

What is haemoglobin A made of?

A

2 alpha and 2 beta chains

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12
Q

What is haemoglobin A2 made of?

A

2 alpha and 2 delta chains

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13
Q

What is haemoglobin F made of?

A

2 alpha and 2 gamma chains

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14
Q

How many Hb molecules foes an rbc contain

A

About 280 million

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15
Q

What is the oxygen-carrying protein in muscle

A

Myoglobin

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16
Q

Write a note on myoglobin
(2)

A

The carrier of oxygen in the muscle

Abundant in the muscles of diving animals like seals and whales -> allows them to continue to use oxygen when underwater

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17
Q

Compare myoglobin and haemoglobin
(2)

A

Both have an additional iron-containing (haem) group

Hb contains four polypeptide chains but myoglobin only has one

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18
Q

When is adult haemoglobin produced

A

Produced after 3-6 months

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19
Q

How many haem groups are in each haemoglobin

A

4 haem

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20
Q

What does haem contain

A

Contains a poryphyrin ring which contains F2++

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21
Q

Where is the haem group found

A

Found within the hydrophobic pocket of the globin chains

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22
Q

What is haem attached to
(4)

A

Attached to histidine residues of globin

Covalently linked to iron

Attached to an atom within the hydrophobic pocket

Covalently linked to the proximal histidine

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23
Q

Where is haem synthesised

A

The mitochondria and the cytoplasm of the developing normoblast

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24
Q

Where is globin synthesised

A

Synthesised by the ribosome

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25
Q

How much of Hb is made up of globin

A

96%

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26
Q

What happens in B-thalassemia

A

Don’t produce B-globin chains

27
Q

Where is the alpha globin gene

A

Chromosome 16

28
Q

Where is the beta, gamma, delta globin genes

A

Chromosome 11

29
Q

Which globin chain genes are found on chromosome 16

A

Alpha
Zeta

30
Q

Which globin chains are found on chromosome 11

A

Beta
Delta
Gamma
Epsilon

31
Q

How is haem synthesised
(4)

A

Glycine and coenzyme A undergo condensation under the action of the key rate limiting enzyme delta-aminolaevulinic acid (ALA) synthase

Pyridoxal phosphate (vitamin B6) is a coenzyme for this reaction which is stimulated by EPO

Protoporyphrin combines with iron in the ferrous (Fe2+) state to form haem, each molecule of which combines with a globin chain made on the polyribosomes

A tetramer of 4 globin chain each with its own haem group in a “pocket” is then formed to make up a haemoglobin molecule

32
Q

What is the first step in haemoglobin synthesis

A

Glycine and coenzyme A undergo condensation under the action of the key rate limiting enzyme delta-aminolaevulinic acid (ALA) synthase

33
Q

What is the limiting enzyme in haemoglobin synthesis
(2)

A

ALA synthase

Delta-aminolaevulinic acid

34
Q

What is the second step in the haemoglobin synthesis

A

Pyridoxal phosphate (vitamin B6) is a coenzyme for this reaction which is stimulated by EPO

35
Q

What is the chemical name of vitamin B6

A

Pyridoxal phosphate

36
Q

What stimulates vitamin B6

A

EPO

37
Q

What is the third step in haemoglobin synthesis
(2)

A

Protoporyphrin combines with iron in the ferrous (Fe2+) state to form haem

Each molecule of which combines with a globin chain made on the polyribosomes

38
Q

What is the fourth step in haemoglobin synthesis

A

A tetramer of 4 globin chains each with its own haem group in a “pocket” is then formed to make up a haemoglobin molecule

39
Q

Describe the genetic control of alpha globin synthesis
(4)

A

Alpha gene cluster is on the short arm of chromosome 16

There are 2 functional alpha gene loci on each chromosome 16: a1 and 12

a1 is responsible for 1/3 of the gene product
a2 is responsible for 2/3 of the gene product

This produces an a chain which is 141 aa in length

40
Q

Describe the genetic control of B globin
(2)

A

B gene locus is on chromosome 11 as well as the 2 gamma and the delta locus

The B gene produces a B chain which is 146 aa in length

41
Q

What supplies iron for Hb synthesis

A

Iron is supplied from circulating transferrin

42
Q

What happens when haem takes on O2
(3)

A

A conformational change takes place

This allows the second haem molecule to by oxygenated more easily and subsequent haem molecules will by oxygenated easier again

This is known as Haem-Haem interaction

43
Q

How saturated is haemoglobin in the lung

A

96% saturated

44
Q

What is the Bohr effect of Hb

A

Hb affinity for oxygen is affected by pH and CO2 concentration

45
Q

What happens to Hb in its deoxygenated state

A

The two B-chains are slightly separated

2,3-diphosphoglycerate enters the Hb molecule

46
Q

What is 2,3-DPG

A

2,3-diphosphoglycerate

47
Q

What happens to 2,3-diphosphoglycerate when Hb gains oxygen

A

2,3-diphosphoglycerate is ejected from haemoglobin

48
Q

Write a note on 2,3-diphosphoglycerate
(3)

A

Its a product derived from anaerobic glycolysis

A regulator of Hb-O2 release

Increased 2,3-DPG increases O2 release

49
Q

Where is 2,3-diphosphoglycerate found in haemoglobin

A

Located in the central cavity of the Hb molecule

Bound to beta chains

50
Q

What is the function of 2,3-diphosphoglycerate

A

To delivery and release oxygen to tissues and the facilitation of carbon dioxide excretion

51
Q

Where in the body is 2,3-diphosphoglycerate low

A

The lungs

52
Q

Where in the body is 2,3-diphosphoglycerate high

A

In tissues

53
Q

What is the oxygen dissociation curve

A

A curve that plots the proportion of Hb in its oxygen saturated form on the vertical axis against the prevailing oxygen tension on the horizontal axis

54
Q

What does the oxygen dissociation curve tell us

A

Important for understanding how our blood carries and releases oxygen

55
Q

What does the oxyhaemoglobin dissociation curve tell us
(2)

A

It relates oxygen saturation (SO2) and partial pressure of oxygen in the blood (PO2)

It determined by Hb affinity for oxygen -> how readily Hb acquires and releases oxygen molecuels into the fluid that surrounds it

56
Q

What would decrease the O2 affinity of Hb
(3)

A

An increase in the amount of CO2 in the blood - this results in O2 being given up more easily

Affinity is decreased in sickle cell anaemia

Affinity is decrease by high body temperature

57
Q

How does high CO2 decrease Hb affinity for O2
(2)

A

CO2 generates hydrogen ions by reacting with water

Reduced O2 affinity results from the combination of H+ with deoxyhaemoglobin

58
Q

What increases O2 affinity for Hb

A

A decrease in 2,3-diphosphoglycerate levels seen in hypoxia -> O2 is given up less readily

59
Q

Why is the O2 affinity of HbF higher than HbA

A

This is because y-chains bind to 2,3-diphosphoglycerate more weakly than B-chains

The high affinity of HbF facilitates O2 transport from the mother to the foetus

60
Q

What are haemoglobinopathies

A

Inherited conditions
Few arise de-novo -> due to mutation

61
Q

What may cause haemoglobinopathies

A

Structural or qualitative defects (SCD/Hb variants)

Quantitative defects (Thalassaemia)
- Hereditary Persistence of Foetal Haemoglobin (HPFH)

62
Q

What are the two types of haemoglobinopathies

A

Qualitative and quantitative haemoglobinopathies

63
Q

What are qualitative haemoglobinopathies

A

Quality of haemoglobin affected

S-haemoglobin seen in sickle cell anaemia

64
Q

What are quantitative haemoglobinopathies

A

Thalassaemia

Quantity of haemoglobin is affected

Not enough B globin chains

2.2 Haematology (38 decks)

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