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haemoglobin structure and function Flashcards

1
Q

what is the primary structure of globin

A

alpha chain has 141 amino acids
beta delta and gamma have 146 amino acids

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2
Q

what is the secondary structure of globin

A

70% of alpha helix

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3
Q

what is the tertiary structure of globin

A

facing of inward non polar residues determines folding

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4
Q

what is the quartenary structure of globin

A

tetrameric, 2 dimers (1 is alpha 1 is beta on top of 2 which is alpha 2, beta ) structure changes on oxygenation allosteric effect

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5
Q

what is the haem structure
what kind of ring with an iron atom at centre

A

protoporphyrin ring

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6
Q

in the haem structure of haemoglobin how many covalent links to nitrogen of pyrrole rings

A

4 covalent links to nitrogen or pyrrole rings

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7
Q

in haem structure how many covalent links to histidine in globin

A

2 covalent links to histidine in globin

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8
Q

why is the distal histidine bond unstable (haem structure)

A

replaced by oxygen co-operative bond) to form oxy-hb

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9
Q

why is h+ and co2 bind to haem

A

to promote o2 release. bohr effect

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10
Q

what does increasing dpg do to haemoglobins affinity for oxygen

A

decreases

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11
Q

how is haem synthesised

A

in red cell precursors mitochondria and cytoplasm
enzyme controlled steps-
glycine and succinate condense to form d-ala delta amino laevulinic acid
porphoblinogen
iron inserts into proto-porphyrin
rate controlling steps
ALA synthase, iron increases rate, haem inhibits

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12
Q

how is globin synthesised

A

globin genes on chromosome 11 and 16
on chromsome 11 fetal gamma2 is alpha 2 on chromosome 16
on chromosome 11 a2 delta 2 is alpha 2 on chromosome 16
on chromosome 11 gene A beta2 is alpha 2 on chromosome 16

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13
Q

how many introns and exons do globin genes have

A

3 exons and 2 introns
splicing machinery recognise sequences then introns removed from transcribed mrna 5’ end of mrna capped so it can attach to ribosomes
3’ end is poly adenylated to stabilise

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14
Q

when is alpha globin produced

A

during early pregnancy

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15
Q

when is beta globin produced

A

near time of birth

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16
Q

what type of globin is not produced after birth

A

gamma globin

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17
Q

when is dpg release increased

A

in response to anaemia, hypoxia
right shift of oxygen dissociation curve so effective oxygen delivery higher p50
sigmoidal shape of curve- changes in po2 at higher levels have little effect on o2 saturation
bohr effect- pco2 increases and ph lowers and so reduction in ph shifts curve to right

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18
Q

what is the bohr effect and how does it change the oxygen dissociation curve

A

the bohr effect is when the carbon dioxide increases and so the ph is lowered, lowering the affinity of haemoglobin for oxygen and so curve shifts to the right.

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19
Q

what are two examples of haemoglobin disorders

A

sickle cell anaemia
beta thalassemia

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20
Q

what is the physiology of thalassaemia

A

reduced production of alpha or beta globin
leads to globin imbalance and precipitation
results in haemolysis in red cells
ineffective erythropoiesis
alpha thalassaemia: 0= deletion of both alpha genes
+= deletion of 1 alpha gene
beta thalassaemia- many non deletional mutations #0 mutations severe so no beta globin synthesis for that allele
+mutations milder so some beta globin synthesis

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21
Q

thalassaemia therapy

A

standard therapy
transfuse for 3-4 weeks
chelate- desferrioxamine
monitor- serum ferritin liver iron conc, heart iron and function organ damage
bone marrow transplantation
gene therapy replacement or beta to gamma switching

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22
Q

sickle cell anaemia

A

autosomal recessive
deoxy haemoglobin forms crystals
heterozygotes have 50% healthy haemoglobin
homozygotes have 100% sickled haemoglobin
vaso-occlusion microvascular obstruction acute crises
chronic progressive organ damage
hbs polymerisation at low po2 causes sickled erythrocytes
they block microcirculation
dynamic reversible process

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23
Q

what are the clinical features of sickle cell anaemia

A

sudden dumping of red cells (sequestrian crises)
spleen infarction

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24
Q

what are clinical features of beta thalassaemia

A

iron overload
bone marrow expansion

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25
Q

what are the complications of sickle cell anaemia

A

-bacteremia
-vaso-occlusion pain
chest syndrome
stroke
chronic organ damage
sickle hand foot syndrome

26
Q

what is the management of sickle cell anaemia

A

prevent and treat acute complications
prevent organ damage
specific anti sickling options transfusion
curative stem cell transplantation or gene therapy

27
Q

how does sickle cell anaemia affect the blood, marrow, spleen, skin, bone , kidney, eye

A

blood- haemolytic anaemia
-marrow- marrow hyperplasia
spleen- hyposplenism
-skin- chronic leg ulcer
bone- avascular hip necrosis osteomyelitis
kidney- chronic renal failure
eye- prolif retinopathy, retinal detachment

28
Q

what is the structure of haemoglobin

A

tetramer containing 2 alpha and 2 beta chains
4 haem groups each haem group binds to an oxygen molecule
structural changes follow oxygen binding (positive co-operativity)

29
Q

what are the three types of haemoglobin molecules

A

haemoglobin A2
adult haemoglobin
fetal haemoglobin

30
Q

what is the structure of fetal haemoglobin

A

2 alpha 2 gamma chains

31
Q

what is the structure of a2 haemoglobin

A

2 alpha 2 delta important to detect beta thalassemia carriers less than 3.5% in adults usually but in beta thalassemia a2 haemoglobin levels are elevated above 3.5%

32
Q

what is the structure of haemoglobin adult

A

2 alpha 2 beta

33
Q

why does fetal haemoglobin have a higher affinity for oxygen than adult haemoglobin

A

gamma chains instead of beta or delta chains give the hb an increased affinity so that it can load oxygen at lower partial pressures in the mothers placenta

34
Q

what is the primary structure of haemoglobin (amino acids)

A

146 amino acids that make up beta gamma delta chains
141 amino acids that make up alpha chains
9 conserved amino acids for oxygen binding

35
Q

what is the secondary structure of haemoglobin

A

70% alpha helix

36
Q

what is the tertiary structure of haemoglobin

A

folding determined by inward facing non polar residues

37
Q

what is the quartenary structure of haemoglobin

A

tetameric made of 2 dimers 1 dimer (alpha 2 beta 2) on top of second dimer (alpha 2 beta 2)
subunit interaction for allosteric effects
structural changes follow oxygen binding

38
Q

explain the structure of haemoglobin in more detail

A

protoporphyrin ring iron atom at the centre
haem iron 6 co-ordinating valencies 4 link to nitrogen of pyrrole rings 2 link to histidine residues in globin
distal histidine bond is unstable estility replaced by oxygen to form oxy-haemoglobin

39
Q

what is the porphyrin

A

4 pyrrole molecules cyclically linked together by methane

40
Q

where is haem synthesised in

A

in mitochondria and cytoplasm of red cell precursors in enzyme controlled steps

41
Q

explain the enzyme controlled steps

A

first step-condensation of glycine and succinate forming delta amino laevulinic acid d-ala

42
Q

explain the intermediate step in haemoglobin synthesis

A

porphobilinogen uroporphobilinogen coproporphyrin 111

43
Q

what is the final step of haemoglobin synthesis

A

insertion of iron into protoporphyrin

44
Q

what is the rate controlling step in haemoglobin synthesis

A

ALA synthesis (iron increases rate, haem inhibits)

45
Q

where are the globin genes present on

A

chromosome 16 chromsome 11

46
Q

what is the gene composition of chromsome 16 downstream up

A

alpha 2 alpha 1 some shape cant disern

47
Q

what is the gene composition of chromsome 11 downstream up

A

beta delta agamma ggamma epsilon

48
Q

what is the significance for why we test for delta haemoglobin for beta thalassemia

A

beta thalassemia causes less synthesis of beta globin and so haemoglobin a2 levels increase they are elevated above 3.5

49
Q

how many exons and introns are present on alpha and beta genes

A

3 exons 2 introns

50
Q

what happens to the mrna after transcription to allow translation

A

5’ of mrna must be capped allowing mrna to attach to ribosomes
3’ end of mrna must be poly andelyated to be stabilised

51
Q

what type of haemoglobin is made in the liver

A

gamma alpha

52
Q

what type of haemoglobin is made in the bone marrow

A

alpha beta

53
Q

what type of haemoglobin is made in the spleen

A

alpha beta gamma

54
Q

explain the binding of oxygen to haemoglobin

A

binding of oxygen to haemoglobin is co-operative binding

55
Q

explain the binding of h+ co2 to haemoglobin

A

h+ binds to haemoglobin forming haemoglobinc acid - lowers affinity of haemoglobin for oxygen promotes oxygen release bohr effect

56
Q

what is the shape of deoxygenated haemaglobin

A

open and taut tense

57
Q

why is the shape of oxygenated haemoglobin different from the shape of deoxygenated haemaglobin

A

oxygenated haemoglobin is compact and relaxed because every time an oxygen molecule binds it breaks the salt bridges

58
Q

what is p50

A

the partial pressure of oxygen in the blood when 50% of haemoglobin molecules are saturated

59
Q

what is the normal p50 value

A

26.6mmhg

60
Q

what is p50 used for

A

to compare affinity of haemoglobin for oxygen

61
Q

what happens to p50 whenthere is a rightward shift of oxygen (decrease in oxygen)

A

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