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2.2 Haematology > Structure and Function of Haemoglobin > Flashcards

Structure and Function of Haemoglobin Flashcards

(64 cards)

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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
How much of Hb is made up of globin
96%
26
What happens in B-thalassemia
Don't produce B-globin chains
27
Where is the alpha globin gene
Chromosome 16
28
Where is the beta, gamma, delta globin genes
Chromosome 11
29
Which globin chain genes are found on chromosome 16
Alpha Zeta
30
Which globin chains are found on chromosome 11
Beta Delta Gamma Epsilon
31
How is haem synthesised (4)
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
What is the first step in haemoglobin synthesis
Glycine and coenzyme A undergo condensation under the action of the key rate limiting enzyme delta-aminolaevulinic acid (ALA) synthase
33
What is the limiting enzyme in haemoglobin synthesis (2)
ALA synthase Delta-aminolaevulinic acid
34
What is the second step in the haemoglobin synthesis
Pyridoxal phosphate (vitamin B6) is a coenzyme for this reaction which is stimulated by EPO
35
What is the chemical name of vitamin B6
Pyridoxal phosphate
36
What stimulates vitamin B6
EPO
37
What is the third step in haemoglobin synthesis (2)
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
What is the fourth step in haemoglobin synthesis
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
Describe the genetic control of alpha globin synthesis (4)
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
Describe the genetic control of B globin (2)
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
What supplies iron for Hb synthesis
Iron is supplied from circulating transferrin
42
What happens when haem takes on O2 (3)
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
How saturated is haemoglobin in the lung
96% saturated
44
What is the Bohr effect of Hb
Hb affinity for oxygen is affected by pH and CO2 concentration
45
What happens to Hb in its deoxygenated state
The two B-chains are slightly separated 2,3-diphosphoglycerate enters the Hb molecule
46
What is 2,3-DPG
2,3-diphosphoglycerate
47
What happens to 2,3-diphosphoglycerate when Hb gains oxygen
2,3-diphosphoglycerate is ejected from haemoglobin
48
Write a note on 2,3-diphosphoglycerate (3)
Its a product derived from anaerobic glycolysis A regulator of Hb-O2 release Increased 2,3-DPG increases O2 release
49
Where is 2,3-diphosphoglycerate found in haemoglobin
Located in the central cavity of the Hb molecule Bound to beta chains
50
What is the function of 2,3-diphosphoglycerate
To delivery and release oxygen to tissues and the facilitation of carbon dioxide excretion
51
Where in the body is 2,3-diphosphoglycerate low
The lungs
52
Where in the body is 2,3-diphosphoglycerate high
In tissues
53
What is the oxygen dissociation curve
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
What does the oxygen dissociation curve tell us
Important for understanding how our blood carries and releases oxygen
55
What does the oxyhaemoglobin dissociation curve tell us (2)
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
What would decrease the O2 affinity of Hb (3)
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
How does high CO2 decrease Hb affinity for O2 (2)
CO2 generates hydrogen ions by reacting with water Reduced O2 affinity results from the combination of H+ with deoxyhaemoglobin
58
What increases O2 affinity for Hb
A decrease in 2,3-diphosphoglycerate levels seen in hypoxia -> O2 is given up less readily
59
Why is the O2 affinity of HbF higher than HbA
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
What are haemoglobinopathies
Inherited conditions Few arise de-novo -> due to mutation
61
What may cause haemoglobinopathies
Structural or qualitative defects (SCD/Hb variants) Quantitative defects (Thalassaemia) - Hereditary Persistence of Foetal Haemoglobin (HPFH)
62
What are the two types of haemoglobinopathies
Qualitative and quantitative haemoglobinopathies
63
What are qualitative haemoglobinopathies
Quality of haemoglobin affected S-haemoglobin seen in sickle cell anaemia
64
What are quantitative haemoglobinopathies
Thalassaemia Quantity of haemoglobin is affected Not enough B globin chains

2.2 Haematology (38 decks)

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