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FM1020 Physiology > Haemoglobin and Myoglobin > Flashcards

Haemoglobin and Myoglobin Flashcards

1
Q

What are globular haemeproteins?

A

Group of specialised proteins that contain haeme as a tightly bound prosthetic group

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2
Q

What is the role of the haeme group in myoglobin and haemoglobin?

A

Oxygen binding

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3
Q

What is the function of the haeme group in soluble guanylyl cyclase?

A

Binding of the vasodilator - nitric oxide

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4
Q

What is the haeme group?

A

Complex of protoporphyrin IX and ferrous iron (Fe++)

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5
Q

What additional bonds may the ferrous iron form in myoglobin and haemoglobin?

A

Histidine amino acid in the associated protein
Oxygen

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6
Q

What is myoglobin?

A

Monomeric 17.8kDa haemeprotein

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7
Q

What is the physiological function of myoglobin ?

A

Reservoir of oxygen within muscle cells to drive muscle contraction during arterial hypoxaemia

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8
Q

What kind of animals have high concentrations of myoglobin?

A

Diving mammals

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9
Q

What structure is found in 80% of myoglobin?

A

8 alpha helices

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10
Q

Where is haeme found in the protein?

A

Tethered into a hydrophobic cleft formed by E & F helices which contain a histidine residue
Proximal H (F8) binds Fe++ in haeme
Distal H (E7) helps stabilise ferrous iron allowing reversible binding of oxygen to Fe++

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11
Q

How many molecules of oxygen may a myoglobin bind to?

A

1 as it contains just 1 haeme group

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12
Q

Where is haemoglobin found?

A

Erythrocytes

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13
Q

What is the structure of the haemoglobin molecule?

A

4 protein subunits with associated haeme group, each structurally similar to myoglobin
2 alpha and 2 beta subunits
One molecule may transport 4 molecules of O2

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14
Q

What 2 forms of haemoglobin exist?

A

Oxyhaemoglobin and Deoxyhaemoglobin

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15
Q

What form does the haeme group take in deoxyhaemoglobin?

A

Non-planar

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16
Q

How far does Fe++ lie outside of the porphyrin plane is deoxyhaemoglobin?

A

0.4 armstrongs

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17
Q

What configuration is found in oxyhaemoglobin?

A

Planar due to Fe++ pulled into plane of porphyrin ring

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18
Q

What other name is given to deoxyhaemoglobin?

A

T form

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19
Q

What other name is given to Oxyhaemoglobin?

A

R form

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20
Q

Why is deoxyhaemoglobin taut?

A

Hydrophobic and ionic bonds constrain relative movement of four subunits

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21
Q

What does the taut form mean for deoxyhaemoglobin?

A

It has a low affinity for oxygen

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22
Q

Why is oxyhaemoglobin relaxed?

A

Movement of ferrous iron into plane of the haeme group causes changes in the quaternary structure of haemoglobin
Hydrophobic and ionic bonds are broken
Increased relative movement of subunits

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23
Q

What is a cooperative system in relation to O2 binding to Haemoglobin?

A

Binding of oxygen to one subunit of the haemoglobin tetramer influence the oxygen binding properties of the other subunits

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24
Q

What is a T-R conformational change caused by?

A

Oxygen binding to one subunit is transmitted to the other 3 monomers in the tetramer… Binding of oxygen to one subunit induces increased binding to the other 3 subunits

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25
Q

Define the partial pressure of O2(Po2).

A

Units of O2 concentration in Blood plasma

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26
Q

What is the Oxyhaemoglobin Dissociation Curve?

A

% Saturation of haemoglobin vs O2 concentration in blood

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27
Q

What shape is the curve in the oxyhaemoglobin dissociation curve and why?

A

Sigmoidal curve due to the cooperative nature ofO2 binding to haemoglobin

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28
Q

What shape is the myoglobin dissociation curve?

A

hyperbolic

29
Q

What is the PO2 and PCO2 in the pulmonary artery?

A

PO2 = 40
PCO2 = 46

30
Q

What is the PO2 and PCO2 in the pulmonary vein?

A

PO2 = 100
PCO2 = 40

31
Q

How many oxygen molecules are released on average at rest from haemoglobin?

A

1

32
Q

What is the oxygen concentration where hypoxia begins?

A

PO2«40mm Hg

33
Q

What is reverse cooperativity?

A

R-T transitions reduce the affinity of other Hb subunits for O2

34
Q

How should one think about oxygen release from haemoglobin?

A

Postage stamp analogy

35
Q

At what tension does the first release of oxygen occur?

A

40 mm Hg

36
Q

What other factors modulate the affinity of haemoglobin for oxygen?

A

pH of Blood
PCO2
2,3 diphosphoglycerate

37
Q

With the other factors, how are they increased?

A

Increased metabolic activity

38
Q

What does acidity and carbon dioxide do to the oxyhaemoglobin curve?

A

Increase in metabolic activity

39
Q

What is the Bohr Effect?

A

Reduction in pH causes protonation of histidine residues on Hb
This allows additional ionic bonds to form between the Hb subunits which stabilises the T form
CO2 group may directly bind to free amino groups on Hb

40
Q

Does a lower pH increase or decrease haemoglobin’s affinity for O2?

A

Decrease

41
Q

Where is the glycolytic pathway the only source of ATP?

A

Hypoxic tissues

42
Q

Where does 2,3 diphosphoglycerate bind to haemoglobin?

A

Pocket of positively charged amino acids formed by the beta subunits which stabilises the T form

43
Q

What does high oxygen concentrations in the lungs do to 2,3-dpg

A

Expels it

44
Q

What does haemoglobin stripped of 2,3 - DPG do to its affinity for oxygen binding?

A

Curve shifts leftwards causing a greater affinity

45
Q

Why is carbon monoxide so dangerous?

A

Haemoglobin has a 200 fold affinity for CO than for O2
It binds to the haeme group and may displace O2 forming carbon monoxyhaemoglobin

46
Q

What are the toxic effects of carbon monoxide?

A

Reduces the overall oxygen transported in blood
At sub-lethal concentrations, binding of CO shifts conformation of other subunits to R form which causes tissue hypoxia

47
Q

What is the major form of haemoglobin in adults?

A

Haemoglobin A

48
Q

What is the minor form of haemoglobin in adults?

A

Haemoglobin A2

49
Q

What is the difference between Haemoglobin A and Haemoglobin A2?

A

Beta subunits in A replaced by closely related delta subunits in A2

50
Q

What form of Haemoglobin is produced during early embryonic development and what subunits are present?

A

Haemoglobin Gower 1
2 teslas and 2 epsilons

51
Q

What form of Haemoglobin is synthesised during foetal development and what subunits are present?

A

Haemoglobin F
2 alphas and 2 gammas

52
Q

Does foetal haemoglobin have a higher or lower affinity to oxygen than Haemoglobin A and why?

A

Higher due to very weak binding of 2,3-DPG which facilitates transfer of O2 across placenta from maternal erythrocytes

53
Q

What is the name of the family of genetic diseases that result in insufficient quantities of haemoglobin molecules and structurally abnormal haemoglobin molecules?

A

Haemoglobinopathies

54
Q

What usually results from haemoglobinopathies?

A

Anaemia

55
Q

Where are the genes for the haemoglobin subunits located?

A

Chromosome 11 and chromosome 16

56
Q

What subunits are produced by Chromosome 11?

A

beta subunits

57
Q

What subunits are produced by chromosome 16?

A

alpha subunits

58
Q

What is sickle cell anaemia caused by?

A

A point mutation in the beta globin gene (valine inserted instead of glutamine)

59
Q

What symbol is given to haemoglobin in a sickle cell anaemia patient?

A

HbS

60
Q

What differs in deoxy-HgS

A

Val6 interacts with Phe85 and Val88 of beta chain of neighbouring molecules resulting in clumping of HbS molecules

61
Q

What happens in Oxy-HgS?

A

Phe85 and Val88 is internalised in the molecule causing no change in the R form

62
Q

What are the signs and symptoms of sickle cell anaemia?

A

Lower PO2 levels in systemic capillaries - aggregation of HgS, RBCs are sickle-shaped, Localised tissue hypoxia, haemolysis
Anaemia
Pain and fever (sickle cell crisis)
Organ damage
severe infections

63
Q

What kind of condition of is Sickle Cell Anaemia?

A

Autosomal Recessive Disorder - Homozygous

64
Q

What is the demographic with the highest rate of sickle cell anaemia?

A

People of African origin

65
Q

Why did sickle cell anaemia evolve?

A

Heterozygous individuals are more resistant to malaria in regions where it is endemic

66
Q

What are Thalassaemias?

A

No production or greatly reduced production of the alpha or beta globin subunits

67
Q

What happens in an individual who is has a homozygous form of beta thalassaemia?

A

Precipitation of “unpaired” alpha subunits leading to death of progenitor RBCs
Ineffective erythropoiesis and severe anaemia

68
Q

What is the progression of alpha thalassaemia?

A

1 defective gene = asymptomatic
3 defective genes = severe haemolytic anaemia
4 defective genes = foetal death

FM1020 Physiology (12 decks)

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