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MCBG > Oxygen Transport > Flashcards

Oxygen Transport Flashcards

1
Q

What molecules can haemoglobin bind? (3)

A

Oxygen
Carbon dioxide
H+

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2
Q

Where is myoglobin present?

A

Skeletal and cardiac muscle

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3
Q

How many haem groups are found in a haemoglobin molecule?
How many oxygen molecules can a Hb molecule bind?

How many haem groups are found in a myoglobin molecule?
How many oxygen molecules can a myoglobin molecule bind?

A

4
4

1
1

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4
Q

What is the structure of a haem group?

A

Fe2+ bonded to 4 nitrogen atoms in the centre of the ring structure

2 additional bonds can be made, 1 bond is made to a histidine residue, the other to an oxygen molecule

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5
Q

What is the structure of myoglobin?

A

Single polypeptide chain

Mainly alpha-helical

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6
Q

How does oxygen bind to a haem group? What change does this result in?

A

Oxygen binds to Fe atom - which usually sits below the plane of the ring
Binding of the oxygen results in Fe atom moving into the plane of the ring —> small change in protein conformation

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7
Q

What type of curve does oxygen binding in myoglobin show?

A

Hyperbolic

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8
Q

What type of curve does haemoglobin binding to oxygen show?

A

Sigmoidal

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9
Q

What is p50?

A

The partial pressure at which there is 50% saturation of myoglobin/haemoglobin with oxygen

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10
Q

What is the structure of a haemoglobin molecule?

A

4 polypeptide chains - 2 alpha and 2 beta

4 haem groups - 4 oxygen molecules

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11
Q

Haemoglobin can exist in which two states?

A

T state - low affinity

R state - high affinity

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12
Q

What stabilises the structure of the T state?

A

Interactions between +ve histidine and -ve aspartate residues

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13
Q

Are Haem groups are more exposed in T or R state haemoglobin?

A

R state

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14
Q

How does binding of oxygen promote stabilisation of the R state?

A

Binding of oxygen pulls fe into the plane of the ring of a haem group resulting in a change in conformation of the Hb molecule - interactions lost due to small rotation and haem groups more exposed for binding

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15
Q

Why is the haemoglobin oxygen curve sigmoidal?

A

Due to cooperative binding of oxygen (cooperativity)

Binding affinity for oxygen increases as the number of oxygen molecules bound increases

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16
Q

What does the sigmoidal binding curve for Hb suggest about the states of haemoglobin in the blood?

A

There is a mixture of Hb in the high and low affinity states

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17
Q

What is the benefit of the sigmoidal curve of Hb for the body?

A

Allows haemoglobin to be more sensitive to small changes in [O2]
Loading/unloading of oxygen is more efficient

18
Q

Shifting of an oxygen binding curve to the left _________ affinity

A

Increases

19
Q

Shifting of an oxygen binding curve to the right _________ affinity

A

Decreases

20
Q

What does the binding of 2,3-bisphosphoglycerate (BPG) result in?

A

Shifts oxygen binding curve to the right
Decreases affinity of Hb to oxygen

Increases efficiency of Hb as an O2 carrier

21
Q

How does BPG bind to Hb?

A

1 molecule of BPG binds to one Hb molecule usually in the centre

22
Q

What happens to [BPG] at high altitudes? Why?

A

Increased concentration. More oxygen is released at the tissues.

23
Q

How does CO2 bind to Hb molecules?

A

Covalently bonds to n-terminus of each chain

24
Q

How do H+ ions bind to Hb?

A

They protonate -ve amino acids

25
Q

What effect does the binding of CO2 and H+ ions have on the affinity of Hb for oxygen?

A

Lowers the affinity

26
Q

How does the Bohr effect help with the supply and demand of oxygen at metabolically active tissues?

A

At metabolically active tissues —> high [H+]

Lower affinity of Hb for oxygen —> oxygen released at respiring tissues

27
Q

How does CO poisoning work?

A

Binds very tightly to Hb and with a higher affinity

Stopping oxygen transport

28
Q

When is CO poisoning fatal?

A

When 50% or more of the Hb is CO bound

29
Q

How does binding of CO to haemoglobin affect other subunits?

A

Increases affinity of unaffected subunits for oxygen

30
Q

What is the structure of HbA and HbF?

A

HbA = adult haemoglobin (vast majority) - 2 alpha chains, 2 beta

HbF = fetal haemoglobin - 2 alpha, 2 gamma chains

31
Q

What are features of HbF?

A

Has a higher affinity than HbA for oxygen - so oxygen passes from the mother to the foetus

32
Q

Sickle cell anaemia is cause by a mutation in which gene?

A

Beta-goblin gene

33
Q

How does the mutation of glutamate to valine in the beta globin gene in sickle cell anaemia, change the structure of the haemoglobin molecule?

A

Results in the formation of a hydrophobic ‘sticky’ pocket

34
Q

How do sickle cell haemoglobin (HbS) interact with other Hb molecules?

A

Polymerises with other Hb molecules causing suckling of RBCs

35
Q

Sickle RBCs are more prone to ______

A

Lysis

36
Q

What are thalassaemias?

A

Group of genetic disorders resulting in incorrect proportions of alpha and beta globin chains

37
Q

What is B-thalassaemia?

A

Decreased/absent b-globin chain production

38
Q

What is a-thalassaemia?

A

Decreased/absent a-globin chain production

39
Q

Is beta-thalassaemia developed before or after birth?

A

Onset after birth

40
Q

Is alpha-thalassaemia developed before or after birth?

A

Before

41
Q

Can B-globin chains form stable tetramers?

A

Yes, with increased affinity for oxygen

42
Q

Can a-globin chains form stable tetramers?

A

No

MCBG (15 decks)

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