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Medical Cell Biology and Genetics > L22- Haemoglobin and myoglobin > Flashcards

L22- Haemoglobin and myoglobin Flashcards

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1
Q

both haemoglobin and myoglobin have functions in

A

oxygen transport

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2
Q

why does oxygen need a transporter to get to tissue

A

veyr insoluble

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3
Q

oxygen binds to …….. and is transported fromt he lungs to the tissue

A

Fe group of Hb

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4
Q

what else can Hb transport back from the tissue in the lungs

A

carbon dioxide and H+ ions

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5
Q

which group in haemoglobin and myoglobin does oxygen bind to

A

haem group

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6
Q

Haem group structure

A
  • protoprophyrin ring , with Fe in the centre surrounded by 4 Nitrogen atoms
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7
Q
A
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8
Q

Fe2+ in the centre of haem can make

A

2 additional bonds to oxygen- one either side of the plane

  • oxygen binds above and below the ring
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9
Q

function of myoglobin

A

faciliates oxygen diffusion throguh muscle tissue

  • local reserve of oxygen during intense exercise
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10
Q

how many polypeptide chains in myoglobin and how many aa

A

one- 153 aa

  • tertiary structure
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11
Q

what sort of protein is myoglobin

A

globular protein

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12
Q

secodnary sturcture of myoglobin

A

75% alpha helical

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13
Q

where is haem prostetic group found in myoglobin

A

in the middle- covalently linked to Fe

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14
Q

a protein is anything larger than

A

100 amino acids

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15
Q

function of haemoglobin

A

contained in RBCs, which efficiently carries oxygen fromt he lungs tot he tissues of the body for respiration

also has a role int ransporting carbond dioxe and hydrogen ions back to the lungs

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16
Q

haemoglobin structure: how many subunits

A

4

  • 2 different types of polypeptide chain
    e. g. alpha2beta 2
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17
Q

haemoglobin structure is an example of

A

quaternary structure

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18
Q

each subunit of hb contains

A

essential haemo prostethic group

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19
Q

conformation of each subunit (polypeptide chain) in Hb is very similar to that of

A

myoglin - similar aa sequence

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20
Q

oxygen biudnding to haem in myoglobin

A

Deoxymyoglobin –> myoglobin

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21
Q

oxygen bidnding to myoglobin show a ….

A

hyperbolic dependence on oxygen concentration

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22
Q

features of oxygen bidning to myoglobin

A

Process is reversible

Constant affinity to oxygen

Most of the O2 is released in active muscle

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23
Q

P50

A

partial pressure giving 50% saturation

24
Q

oxygen dissocaition curve for myoglobin vs haemoglobin

A

Myoglobin has a much higher affinity to oxygen than haemoglobin

25
Q

why are the oxygen dissociation curves for myoglobin and haemoglobin different

A

Haemoglobin doesn’t have a constant affinity to oxygen – T –> R state

26
Q

what structureal changes happen to Hb on binding to oxygen

A

deoxyhaemoglbin can exist in low affinity T state or high affinity R state

Oxygen binding promotes stabilisation of the R state (i.e. why the graph has a low gradient at first)

27
Q

T state

A

low affinity

28
Q

R state

A

high affinity

29
Q

why is the oxyegn bidnding curve for haemoglobin sigmoidal instead of hyperbolic?

A

The binding of one oxygen molecule causes a conformational change in one subunit which promotes the binding of subsequent molecules

(e.g. T–> R state)

30
Q

The binding of one oxygen molecule causes a conformational change in one subunit which promotes the binding of subsequent molecules also known as

A

Cooperative binding of oxygen to Hb

31
Q

why is the sigmoidal curve of Hb important

A

means O2 can be efficiently carried from the lungs to the tissue

More sensitive to small difference in oxygen conc

32
Q

if Hb was in a constant R state (high affinity)

A

wouldn’t work: oxygen would bind too tightly and not be given up to respiring tissue

33
Q

if Hb was in a constant T state (lower affinity)

A

wouldn’t work: woudlnt bind oxygen well e.g. only 50% saturated- not enough oxygen in tissue

34
Q

If haemoglobin showed No cooperativity

A

– Hb would be 60% saturated after passing the lungs and would only release 38`% to the tissues

35
Q

If haemoglobin shows cooperativity (Sigmoidal)

A
  • picks up oxygen really well, transporting twice as much oxygen than with no cooperativity and releases it really well
36
Q

Gain and release of oxygen by Hb is a tightly regulated process. Which molecules affects Hb affinity for oxygen? (2)

A
  1. 2,3,- bisphosphoglycerate (BPG)
  2. H+ ions
37
Q

the oxygen binding curve for pure haemoglobin is

A

different than the oxyegn bdidning cruve for hameoglobin found within RBCs

38
Q

the cuvre for haemoglobin in RBC is

A

shifted tot he right with respect to the pure Hb curve

  • implying that pure Hb has a much higher afffinity for oxygen and will release much less (only 8%) of oxygen to exercising tissue (comapred to 66% for Hb in RBC)
39
Q

2,3- Bisphosphoglycerate acts as an …….. of Hb

A

allosteric effector

40
Q

what is 2,3-BPG

A

is a naturally occurring molecule that is produced as an intermediate in the glycolysis process.

41
Q

what does 2,3-BPG do

A

bidns to the centre pocket found in Hb, stabilisiing the T-state of Hb

42
Q

2,3-BPG affect on Hb affinity for oxygen

A

stabilises the T state (low affinity)

  • decreasing Hb affinity for oxygen
  • shifting the entire oxygen-bdinding curve to the right side
43
Q

BPG allows

A

Hb to act as an effective oxygen carrier in the body- unloading about 66% of oxygen to exercising tissue

44
Q

what does the oxygen dissociation curve look like with and withou BPG

A

with BPG- sigmoidal

without BPG- hyperbolic

45
Q

charge of BPG

A

negatively charged- can bind with positivly charged haem

46
Q

BPG and altitude

A

At high altitudes- BPG concentration increases- promoting oxygen release in tissues

  • At high altitude lower ppO2
  • BPG shifts curve to the right
  • Picks up less oxygen from the lungs (slighlty)
  • But able to release about the same amount to the tissues due to lower affinity
47
Q

why atheletes train at high altitudes

A

increase in BPG and RBC production

  • 2,3-BPG is elevated in high altitudes, meaning Hb has a lower affinity for oxygen, releasing it more efficiently to respiring tissue.
  • Haemoglobin content also increases (more RBC) so that higher amounts of oxygen can be captured.
48
Q

carbon dioxide and H+ ions (acidic) affect on Hbs affinity for oxygen

A
  • have the same affect as BPG
  • lower Hbs affinity for oxygen
49
Q

both CO2 and H+ bind to

A

Hb but not myoglobin

50
Q

why do carbon dixodie and hydr0ogen ions not bind myoglobin

A

Myoglobin cannot exhibit the Bohr effect- only consists of a single polypeptide

Only in Hb- quaternary structure – cooperative effect

51
Q

where is CO2 and H+ effect on Hb important

A

in active tissue

  • local pH decline in metabolically acitve tissues due to the release of H+ and CO2
  • decreases affinity Hb has for oxygen
  • icnreases the release of oxygen from Hb
52
Q

Hb has a lower affiity for oxygen at

A

lower pH (i.e. when tissue is metabolically active)

53
Q

why is CO a poison

A

CO is a poison because it combines with ferromyoglobin and ferrohaemoglobin and blocks oxygen transport

54
Q

CO binds to haemoglonbin …… more readily than oxygen

A

x250

55
Q
A
56
Q

when is CO poisoning fatal

A

when COHb is >50%

  • binds more strongly and longer than oxygen
57
Q

treatment for CO poisoning

A
  • blood transfusion
  • hyperbarix oxygen therapy

Medical Cell Biology and Genetics (33 decks)

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