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Medical Cell Biology & Genetics > Haemoglobin & Myoglobin > Flashcards

Haemoglobin & Myoglobin Flashcards

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1
Q

Why must oxygen bind a transporter to be transported around the body?

A

It is not very soluble in water

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2
Q

Describe the features of myoglobin structure.

A

It is a single polypeptide made 153 amino acids and is mainly (75%) alpha-helical - histamine 93 in the 8th alpha helix is covalently linked to the iron

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3
Q

Describe the structure of haem. Which part binds oxygen?

A

Haem is composed of a protoporphyrin ring and an iron ion attached to 4 nitrogen molecules - the iron ion (Fe2+) is what attaches to the oxygen molecule

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4
Q

How many molecules bind the haem group in haemoglobin and myoglobin?

A

1 molecule of oxygen

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5
Q

How is the iron ion bound to the protoporphyrin ring in a haem molecule?

A

The iron ion is attached to the protoporphyrin ring via a histidine residue

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6
Q

How does oxygen binding cause a change in the configuration of a myoglobin molecule?

A

In its deoxygenated form, the iron ion sits slightly below the plane of the protoporphyrin ring of myoglobin - when oxygen binds, it causes a conformational change causing the iron ion to punch upwards into the same plane of the protoporphyrin ring

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7
Q

What is the P50?

A

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

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8
Q

Describe some features of the structure of haemoglobin.

A

An assembly of 4 globular protein subunits - 2 alpha subunits and 2 beta subunits - each subunit contains a haem group which can bind a single oxygen molecule - haemoglobin can therefore bind 4 oxygen molecules

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9
Q

In what 2 states can deoxyhaemoglobin exist? Which state does oxygen binding promote?

A

In a low affinity T state or a high affinity R state - oxygen binding promotes stabilisation of the R state

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10
Q

How does oxygen-binding affect the conformation of haemoglobin?

A

Oxygen-binding instigates a conformational change that rotates all subunits by around 15 degrees - the haem groups become much more exposed, so oxygen can bind easier - this changes the haemoglobin from the T state to the R state - like myoglobin, the conformational change pushes the iron group into the same plane as they protoporphyrin ring

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11
Q

On an oxygen dissociation curve, what does a shift in the curve to the right mean?

A

Myoglobin/haemoglobin has a lower affinity for oxygen binding

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12
Q

On an oxygen dissociation curve, what does a shift in the curve to the left mean?

A

Myoglobin/haemoglobin has a greater affinity for oxygen binding

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13
Q

Why is the oxygen binding curve for haemoglobin sigmoidal?

A

Due to the allosteric changes that oxygen binding induces (rotating the haem groups by 15 degrees) - the binding affinity for oxygen increases as each oxygen molecule binds - the binding of the 1st oxygen molecule is hard, while the binding of the 4th oxygen is relatively easier - this then produces the sigmoidal curve seen on the oxygen binding curve

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14
Q

What does ‘co-operative’ binding of oxygen to haemoglobin describe?

A

The binding of one oxygen molecule promotes the binding of subsequent oxygen molecules

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15
Q

What is the role of 2,3 bisphosphoglycerate (BPG)?

A

BPG changes the affinity of haemoglobin for oxygen, making it a more efficient transporter of oxygen - it actually decreases the affinity of haemoglobin for oxygen

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16
Q

What are general levels of BPG present in red blood cells?

A

Around 5nm

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17
Q

How many molecules of BPG bind per haemoglobin tetramer?

A

1 molecule of BPG binds per haemoglobin tetramer

18
Q

How are BPG concentrations affected at high altitudes?

A

BPG concentrations are greater at higher altitudes, which promotes oxygen dissociation from haemoglobin at tissues

19
Q

How does BPG affect the position of an oxygen dissociation curve?

A

It will shift the curve to the right

20
Q

How does binding of hydrogen and carbon dioxide affect the affinity of haemoglobin for oxygen?

A

Their binding decreases haemoglobins affinity for oxygen

21
Q

How does carbon dioxide (CO2) bind haemoglobin?

A

Carbon dioxide covalently attaches to the N-terminus of haemoglobin

22
Q

What is the Bohr Effect? What does this ensure?

A

The Bohr Effect suggests that the H+ and CO2 produced by metabolically active cells produce acidic conditions (via lactate and carbonic acid) that encourage the dissociation of oxygen (and association of CO2) to haemoglobin - this ensures the delivery of O2 is proportional to its demand

23
Q

How does a pH increase affect an oxygen dissociation curve?

A

It will shift the curve to the right, which decreases the affinity its of haemoglobin for oxygen

24
Q

Why is carbon monoxide a poison?

A

It combines with ferromyoglobin and ferrohaemoglobin and blocks oxygen transport, leading to cell death

25
Q

How much more readily will haemoglobin bind with carbon monoxide than oxygen?

A

Carbon monoxide binds haemoglobin 250X more readily than oxygen does

26
Q

When does carbon monoxide binding become fatal?

A

When 50% of haemoglobin are bound to carbon monoxide

27
Q

What mutation leads to sickle cell anaemia? Why is this mutation so detrimental?

A

A mutation of glutamate to valine in a beta globin - valine is highly hydrophobic and so buries itself within the globin - 2 ‘sickle cells’ may bind to try and mask their hydrophobic regions, giving the sickle cells their ‘sticky’ characteristics - furthermore, this is exacerbated in their low-affinity deoxygenated state, and so cluster is a deoxygenated state

28
Q

What are 2 pathologies of sickle cells?

A

Sickle cells are more likely to lyse, leading to anaemia - they are also more rigid, and tend to block vasculature

29
Q

What are thalassaemias? Are they heterozygous or homozygous?

A

Thalassaemias are a group of genetic disorders where there is an imbalance between the number of alpha- and beta- globin chains - heterozygotes are only minor lay affected - homozygous are greatly affected

30
Q

Describe the pathology of B-thalassaemias.

A

B-thalassaemias describe a decreased or absent production of beta globins - alpha globins are unable to form stable tetramers

31
Q

When do the symptoms of B-thalassaemias first appear?

A

Symptoms appear after birth

32
Q

How does an A-thalassaemia affect an individual?

A

A-thalassaemias involve a decrease or absence of alpha globin subunits - instead, beta tetramers can form functioning tetramers, with an increased affinity for oxygen

33
Q

When is the onset of an A-thalassaemia?

A

Onset is before birth

34
Q

Discuss haemoglobin in foetal blood.

A

Haemoglobin in foetal blood (HbF) has a greater affinity for oxygen than maternal blood (HbA), which allows oxygen transfer from maternal haemoglobin to foetal haemoglobin

35
Q

In comparison to HbA, where does the oxygen dissociation curve of HbF lie?

A

The oxygen dissociation curve of foetal haemoglobin (HbF) lies to the left of maternal haemoglobin (HbA)

36
Q

On which chromosome are alpha-globin-like genes found? On which chromosome are beta-globin-like genes found?

A

Alpha-globin-like genes are found on chromosome 16 - beta-globin-like genes are found on chromosome 11

37
Q

Describe the composition of normal adult haemoglobins.

A
  • 90% HbA (2A2B) - (2alpha2beta)
  • 2% HbF (2A2Y) - (2alpha2gamma)
  • 2-5% HbA2 (2A2D) - (2alpha2delta)
38
Q

Does foetal or maternal haemoglobin have a greater affinity for oxygen under physiological conditions? Where will their oxygen dissociation curves lie in comparison to one another?

A

Foetal haemoglobin has a greater affinity for oxygen under physiological conditions - a foetal oxygen dissociation curve will therefore lie to the left of a maternal oxygen dissociation curve

39
Q

What is the effect of BPG on haemoglobins affinity for oxygen?

A

BPG decreases the affinity of haemoglobin for oxygen

40
Q

Does adult or foetal haemoglobin have a greater affinity for BPG?

A

Adult haemoglobin (as it must have a method to aid offloading to foetal haemoglobin)

41
Q

What vitamin is an analogue of warfarin?

A

Vitamin K

Medical Cell Biology & Genetics (11 decks)

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