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Fundamentals of pathology > Haemoglobin structure and function > Flashcards

Haemoglobin structure and function Flashcards

1
Q

What is the structure of haemoglobin

A

4 polypeptide chains; 2 alpha and 2 beta

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2
Q

What are haemproteins

A

A group of specialised proteins that contain haem as a tightly bound prosthetic group

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3
Q

What is haem

A

Is a complex of protoporphyrixin IX and ferrous iron (Fe2+)

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4
Q

How is iron held in the centre of haem molecule

A

By bonds to the 4 nitrogen of a porphyrin ring

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5
Q

Where is haemoglobin synthesised

A

65% in the erythroblasts

35% in the reticulocyte stage

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6
Q

How is the synthesis of haemoglobin regulated

A

Regulated by tissue hypoxia since hypoxia causes the kidneys to increase production of of erythropoietin, which increases RBC and Hb production

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7
Q

Where is haem synthesised

A

In the mitochondria

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8
Q

How is iron delivered to the reticulocyte

A

Transferrin

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9
Q

Where are protoporphyrins synthesised

A

In the mitochondria of RBC precursors

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10
Q

What is the synthesis of protoporphyrins regulated by

A

Mediated by erythropoietin and vitamin B6

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11
Q

What makes a haem molecules

A

Protoporphyrin + Iron

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12
Q

Where does globin synthesis occur

A

The polyribosomes (polysomes)

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13
Q

How doe proper globin synthesis depend on genes

A

The precise order of amino acids in the globin chains is critical to the structure and function of haemoglobin

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14
Q

Where are beta-cluster globin genes found

A

The short arm of chromosome 11

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15
Q

Where are alpha-cluster globin genes found

A

The short arm of chromosome 16

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16
Q

What are the different types of beta-cluster genes

A

Beta, gamma, delta and epsilon genes

17
Q

What are the different types of alpha-cluster genes

A

Alpha and zeta genes

18
Q

What can mutations to just one amino acid have on a large scale

A

Sickle cell disease

19
Q

What is the cause of thalassaemias

A

Reduced synthesis of moral or beta globin chains

20
Q

When does globin synthesis begins

A

3 weeks after gestation

21
Q

What are the different type of embryonic haemoglobin

A

Gower I - zeta & epsilon
Gower II - alpha & epsilon
Portland I - zeta & gamma
Portland II - zeta & beta

22
Q

What are the different types of foetal haemoglobin

A

HbF - alpha & gamma

HbA - alpha & beta

23
Q

What are the different types of adult haemoglobin

A

HbA2 - alpha & delta
HbF - alpha & gamma
HbA - alpha & beta

24
Q

What happens to the haemoglobin in the embryonic stage and where is it synthesised

A

Produced by the yolk sac
Alpha haemoglobin increases and maintains a high concentration throughout, epsilon haemoglobin is initially high and then drops completely before foetal stage

25
Q

What happens to haemoglobin in the foetal stage and where is it synthesised

A

Produced by the liver and spleen

Gamma haemoglobin increases but gradually drops before and after birth

26
Q

What happens to haemoglobin in the adult stage and where is it synthesised

A

Produced by the bone marrow

Beta haemoglobin increases from birth

27
Q

What does haemoglobin act as a buffer

A

Maintains the blood pH as it changes from oxyhaemoglobin to deoxyhaemoglobin

28
Q

What does globin do

A

Protects haem from oxidation, gives solubility and permits variation in affinity

29
Q

What happens to haemoglobin when its oxygenated

A

2,3-DPG is pushed out, the beta chains move closer

30
Q

What happens when oxygen is unloaded

A

The beta chains are pulled out, permitting the entry of 2,3-DPG resulting in a lower affinity of O2

31
Q

What does the amount O2 bound to haemoglobin and released to tissues depend on

A

PO2, CO2 and the affinity of haemoglobin for O2

32
Q

What is oxygen affinity

A

The ease with which haemoglobin binds and releases oxygen

33
Q

What is the shape of the disassociation

A

Sigmoid shape

34
Q

What is the Bohr effect

A

In acidic pH, the curve shifts to the right, resulting in an enhanced capacity to release O2 where it is needed

35
Q

What happens in a right shift

A
  • Increased partial pressure of oxygen; low pH, high 2,3-DPG binding and high temperature
  • Decreased affinity for O2
  • Hb willing to release O2 to tissues
  • E.g. anemia and acidosis
  • Even though there may be less RBCs, they act more efficiently to deliver O2 to target
36
Q

What happens in a left shit

A
  • Decreased partial pressure of oxygen; high pH, low 2,3-DPG binding and low temperature
  • Increased affinity for oxygen
  • Hb is less willing to release O2 to tissues
  • Eg. Presence of abnormal Hb’s, alkalosis
37
Q

What does the normal position of the curve depend on

A
  • concentration of 2,3-DPG
  • H+ ion concentration
  • CO2 in RBC
  • Structure of Hb
  • Standard conditions = 37 C, 7.40 pH and Base excess is 0 (the amount of CO2 needed to neutralise the acid)
38
Q

What are the 3 mechanisms of carbon dioxide transport

A
  1. Dissolution in the plasma
  2. Formation of carbonic acid
  3. binding to form carbaminohaemoglobin
39
Q

How does carbon dioxide bind to haemoglobin

A

Binds irreversibly at the N-terminal group of the alpha chains of Hb
Carbonated-Hb has a lower affinity of oxygen affinity

Fundamentals of pathology (4 decks)

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