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FMS > [FMS] CBS - Haemoglobin > Flashcards

[FMS] CBS - Haemoglobin Flashcards

1
Q

what is the structure of adult haemoglobin HbA

A

Hb is a tetramer : 2 identical beta globin subunits and 2 identical alpha globin subunits

Hb is dimer of a dimer (α1β1)(α2β2)

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2
Q

Why is oxygen a key component of ATP generation?

A

final electron acceptor in oxidative phosphorylation

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3
Q

which has higher affinity? Mb or Hb

A

AFFINITY: Mb > Hb

becuase Mb is fully saturated at a lower oxygen level (partial pressure of oxygen: pO2)

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4
Q

how many bonds can fe2+ bind with in Hb, and to what specifically?

A

Fe2+ (ferrous) ion can bond with six ligands:

  • four by nitrogen atoms of haem group
  • fifth by attachment to specific histidine of globin
  • sixth is available for the reversible attachment of oxygen
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5
Q

2 forms of Hb

A

Oxyhaemoglobin (oxyHb)
Deoxyhaemoglobin (deoxyHb)

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6
Q

what prevents the oxygen from oxidising Fe2+ to Fe3+

A

Hydrophobic residues found in interior of globin prevents oxygen from oxidising the Fe2+ to Fe3+

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7
Q

what type of Fe ion can’t bind to oxygen, and what is it called?

A

Haem with Fe3+ is unable to bind oxygen
This is met-haemaglobin (metHb)

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8
Q

name of the oxygen saturation curve for Hb

A

sigmoid shape (S)

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9
Q

what kind of binding does the oxygen saturation curve for Hb show?

A

cooperative binding and an example allostery.

^ Allostery occurs when the binding of oxygen to one globin changes the shape of the binding site of another globin.

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10
Q

what needs to be high in order for Hb to be fully saturated?

A

When pO2 (partial pressure of oxygen) is high cooperative binding allows Hb to be fully saturated.

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11
Q

2 forms of globin subunits

A

Each globin subunit can exist in two forms (states):
T (tense)
R (relaxed)

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12
Q

what does T (tense) and R (relaxed) mean in terms of affinity

A

T (tense) conformation with low affinity for oxygen.

R (relaxed) conformation with high affinity for oxygen.

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13
Q

when oxygen binds to a1 what happens, and what happens to the affinity of B1?

A

Binding of oxygen to α1 changes the conformation of α1
⬇
Binding of oxygen to α1 changes β1 to R state.
⬇
THEREFORE β1 has increased affinity for oxygen.

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14
Q

what is the bohr effect?

A

Ability of haemoglobin to bind oxygen decreases as the [H+] increases.

Ability of haemoglobin to bind oxygen decreases as the pH decreases.

THEREOFRE H+ and Ph effects how Hb binds to oxygen

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15
Q

which part of the body releases most oxygen?

A
  • peripheral tissues release most O2 (away from lungs)
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16
Q

what happens when theres a loss of the bohr effect?

A

hyperventilation

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17
Q

how does loss of bohr effect lead to hyperventilation

A
  1. more expiration of CO2
    1. CO2 level in plasma reduced = hypocapnia
    2. less H2CO3
    3. [H+] drops / pH increases
    4. No protons = Bohr effect does not operate
    5. Less O2 released to peripherical tissues
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18
Q

what are the 3 types of Hb

A
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19
Q

why does HbF have higher affinity than HbA?

A

so in placenta HbF is able to be saturated in preference to HbA .

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20
Q

order of affinities for Mb, HbA, HbF

A
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21
Q

what is BPG

A

2, 3 - bisphosphoglycerate (BPG) is allosteric regulator of oxygen binding of haemoglobin.

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22
Q

how is BPG generated

A

BPG is generated by metabolising tissues.

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23
Q

where does BPG bind to, and in what state?

A

BPG is negatively charged so binds to positively charged pocket but ONLY IN T-STATE!! (deoxyHb).

24
Q

is BPG positively or negatively charged

A
  • BPG negatively charged
25
Q

when BPG binds to Hb what happens to its affinity?

A

Binding of BPG LOWERS the affinity of Hb for oxygen.

26
Q

is SCD a dominant or recessive disease?

A
  • recessively inherited
27
Q

how is SCD characterised?

A

characterised by formation of sickle shaped cells

28
Q

what mutation causes SCD

A

mutation of beta-globin from GLU to VAL on the 6th position on surface

GLU is acidic, hydrophilic but VAL is hydrophobic and polar

29
Q

difference in shape between HbA and HbS

A

In HbA glutamic acid is stabilised by hydrogen bonds with aqueous environment

In HbS to prevent valine being in an aqueous environment two haemoglobins aggregate together
^ This aggregation continues to form polymers

30
Q

what does the sickle shaped cells do? why are they bad?

A

Sickle shaped cells can be trapped in capillaries and lyse

31
Q

low fe2+ intake in the diet leads to what disease?

A

anaemia

32
Q

high levels of plasma glucose cause what disease?

A

diabetes type 1

33
Q

what disease is caused by an imbalance of globin chain production.

A

Hereditary haemolytic anaemia

34
Q

what disease is caused by deficient beta-globin production

A

beta-thalassaemia

35
Q

what disease is caused by deficient alpha-globin production

A

alpha-thalassaemia

36
Q

what disease is caused by the mutations of developmental expression of gamma gene

A

Hereditary persistence of fetal haemoglobin (HPFH)

37
Q

what is the name of the ring in the heme group structure

A

prophoryin ring

38
Q

defects in heme synthesis leads to what disease?

A

Porphyria

39
Q

Mb is fully saturated at a ___ oxygen level

A

lower

40
Q

DO HAEMOGLOBIN QUIZ ON KEATS THEN RESUME FLASHCARDS

A

https://keats.kcl.ac.uk/mod/quiz/view.php?id=7540248

41
Q

try the Hb quiz on keats and come back

A

https://keats.kcl.ac.uk/mod/quiz/attempt.php?attempt=4370706&cmid=6619916

42
Q

What state is oxyHb in at physiological pH?

A

OxyHb is more acidic (pKa 6.8) and at physiological pH it is dissociated.

43
Q

How can oxygen be stored?

A

In striated muscles bound to myoglobin (Mb)

44
Q

What are globins?

A

Globins are around 150 amino acids in length consisting of alpha helices.

They also include a haem group buried within a hydrophobic pocket.

45
Q

What side of the haem group faces the surface of the globin?

A

The hydrophilic side of the haem group faces the surface of the globin.

46
Q

What is carbon dioxide converted to?

A

Most carbon dioxide is converted to carbonic acid by carbonic anhydrase in erythrocytes.

  • The carbonic acid then dissociates into bicarbonate (HCO3- and H+).
  • Bicarbonate is then exported via Cl-/HCO3- channel.

Some carbon dioxide reversibly binds to Hb to form carbaminoheamoglobin.

47
Q

What is the effect on haemoglobin as [H+] increases?

A

Ability of haemoglobin to bind to oxygen decreases as the [H+] increases.

48
Q

What is the effect on haemoglobin as the pH decreases?

A

The ability of haemoglobin to bind to oxygen decreases as the pH decreases.

49
Q

What does the impact of oxygen saturation have on H+ binding of haemoglobin in lungs?

A
  • Increase in [H+] within the erythrocytes shifts the dissociation of bicarbonate towards carbonic acid.
    • HCO3- + H+ → H2CO3
  • Increase in carbonic acid shifts the equilibrium of carbonic anhydrase towards carbon dioxide.
    • H2CO3 → H2O + CO2 (reversible reaction)
  • Carbon dioxide is expired.
50
Q

What is the percentage of HbA and HbF at birth?

A

20% HbA and 80% HbF.

51
Q

What is the oxygen binding curve of HbA in absence of BPG similar to.

A

Myoglobin (Mb).

52
Q

in transport of CO2 how much is dissolved in blood

A

10%

53
Q

in transport of CO2 how much is converted to bicarbonate

A

60%

54
Q

in transport of CO2 how much is bound to Hb

A

30%

55
Q

Which is a better buffer oxy or deoxy for the H+ produced in metabolism?

A

DEOXY IS BETTER - It is less dissociated (more protonated) than oxyhaemoglobin at the pH of blood

FMS (33 decks)

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