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509 - Cellular and Transfusion Science > Haemoglobin structure and synthesis > Flashcards

Haemoglobin structure and synthesis Flashcards

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1
Q

Why doesn’t Hb get carried free in circulation?

A

The large molecules could make the fluid highly viscous and hard to circulate

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2
Q

What are the two major structures in Hb?

A

Goblin chains
Prosthetic group Haem

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3
Q

What structure does haem have?

A
  • Tetrameric structure
  • Tetrapyrolle ring structure
  • Fe(II) at centre
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4
Q

What is step one of Haem synthesis?

A
  • Formation of Aminolaevulinic Acid (ALA)
  • Condensation reaction
  • ALA synthase involved
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5
Q

What is step two of Haem synthesis?

A
  • Condensation reaction to form Porphobilinogen (PBG)
  • ALA dehydratase involved
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6
Q

What is step three of Haem synthesis?

A
  • Polymerisation of PBG
  • x4 PBG come together to form a tetra-pyrolle ring structure
  • Two enzymes involved: PBG Deaminase and Uroporphyrinogen III Cosynthetase
  • One pyrolle ring is reversed during this process
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7
Q

What is step four of Haem synthesis?

A
  • Decarboxylation
  • Acetyl to Methyl through loss of CO2
  • x4 CO2 liberated
  • Enzyme used: uroporphyrinogen III decarboxylase
  • last stage to occur in cytoplasm
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8
Q

What is step five of Haem synthesis?

A
  • Conversion of proprionyl to vinyl
  • Uses coproporphyrinogen oxidase
  • oxidative decarboxylation + dehydrogenation of two propionyl groups at 2, 4, positions
  • Molecular oxygen rewuired
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9
Q

What is step six of Haem synthesis?

A
  • Oxidation, removal of 6H+ atoms
  • Uses protoporphyrinogen oxidase
  • Some rearrangement to double bonds
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10
Q

What is step seven of Haem synthesis?

A
  • Insertion of Fe(II) into ring
  • Use ferrochelatase/haem synthetase
  • Specific to ferrous form of iron
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11
Q

Where does each stage of haem synthesis occur?

A

Stages 1-4 = Cytoplasm

Stages 5-7 = mitochondria

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12
Q

How is iron absorbed?

A
  • Divalent metal transporter-1 (DMT-1)
  • Absorbed by membranes of the duodenum
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13
Q

What transports Fe out of cells?

A

Ferroportin

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14
Q

In what state is Iron most effectively carried?

A

Fe3+

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15
Q

How can Iron enter developing RBCs?

A

Fe-Tr complex can only enter by binding Transferrin receptor (TfR)

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16
Q

What regulates Ferroportin?

A

Hepcidin

17
Q

Outline Hepcidin

A
  • Produced by liver
  • Leads to degradation of ferroportin
  • 25 amino acid peptide, HAMP gene, chrom. 19
  • Raised levels = anemia of chronic disease
18
Q

Which pathway do erythrocytes rely on for energy? Outline it

A

Embden-Meyerhof

  • Glycolysis of glucose to pyruvate
  • Free energy forms ATP
  • Leaves oxygen free due to lack of mitochondria
19
Q

How many levels of structure does Hb have?

A

Polymeric, so four (primary, secondary, tertiary, quaternary)

20
Q

What families do globin chains derive from?

A

Alpha and beta chain families

21
Q

How many globins do Hb molecules contain

A

2 from each family

22
Q

Where are the globin genes found?

A

Long arms of chromosomes 11 and 16

23
Q

Outline the beta globin chain family

A
  • β, γ, δ, and ε
  • 146 amino acid length
24
Q

Outline the alpha globin chain family

A
  • α and ζ
  • 141 amino acid length
25
Q

Where are amino acid residues found?

A
  • Areas of contact between globins/ globin and the haem group
26
Q

Outline the secondary structure of Hb

A
  • 75% of alpha and beta globin chains form alpha-helices
  • Remaining 25% are residues connecting helices
27
Q

Outline the tertiary structure of Hb

A
  • Amino acids on the outside of the protein are hydrophilic (so can remain in solution)
  • Glucose-6-phosphate Dehydrogenase (G6PD) maintains NADPH
  • G6PD deficiency results in lack of oxidative stress management
28
Q

What are heinz bodies?

A

A structure containing denatured Hb caused by oxidant damage

29
Q

Outline the quaternary structure of Hb

A
  • Only has this structure as Hb is a polymer made of 4 monomers
  • Hydrophobic bonds between adjacent areas
  • Main contact between B and H helices
  • Functional contacts allow conformational changes
30
Q

How does Fe(II) move in Hb depending on the oxygen state?

A

Deoxygenated: slightly above plane of haem moiety

Oxygenated: into the plane of the porphyrin group

31
Q

What is the function of 2,3-Biphosphoglycerate (2,3-BPG)?

A
  • Found in large amounts in RBCs
  • Binds to beta chains in centre of thr tetramer
  • combines with deoxyHb to reduce Hb affinity for O2
  • Reversibly bound
32
Q

What factors effect oxygen binding affinity?

A

Using bohr effect:
- PCO2
- PO2
- pH
- Temperature
- 2,3-BPG

33
Q

Why does foetal Hb have a greater affinity for O2?

A

It binds less easily to 2,3-BPG, allowing it to carry 20-30% more O2 than maternal HbA.

509 - Cellular and Transfusion Science (15 decks)

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