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Semester 1 - MCBG > 15. Oxygen Transport > Flashcards

15. Oxygen Transport Flashcards

1
Q

What 3 molecules can haemoglobin transport?

A

Oxygen
Carbon dioxide
H+

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2
Q

Why does oxygen need a transport molecule?

A

• Oxygen does not diffuse well between large distance because it is insoluble so wont dissolve in blood

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3
Q

Wher is myoglobin present?

A

In muscle

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4
Q

Where does oxygen bind to the haemoglobin and myoglobin?

A

To the Fe atom on the haem group

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5
Q

What does a haem consists of?

A

Haem consists of a protoporphyrin ring and an Fe atom bound to 4 N atoms of the ring

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6
Q

How many bonds can Fe2+ make with oxygen?

A

Fe2+ can make 2 additional bonds to oxygen , one on either side of the plane

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7
Q

How many oxygen molecules bind to a haem group?

A

1

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8
Q

How is the Fe atom bound to the haemoglobin protein?

A

Fe atom is bound to the protein via a histidine residue (proximal histidine) on the other side of the ring

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9
Q

Describe the myoglobin structure

A
  • Small protein
  • Compact
  • Globular
  • Single polypeptide chain
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10
Q

What is an alpha helix?

A

A right handed helix that is stabilised by the hydrogen bonds between the backbone CO and NH groups in the polypeptide chain.

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11
Q

Describe how oxygen binds to haem in myoglobin?

A
  1. Fe in deoxymyoglobin is slightly below the plane of the ring
  2. Oxygen binding causes movement of Fe into plane of the ring
  3. Movement causes movement of His F8 and small change in overall protein conformation
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12
Q

What type of dependence does oxygen binding to myoglobin show?

A

Oxygen binding to myoglobin shows a hyperbolic dependence on oxygen concentration

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13
Q

Why is the oxygen dissociation curve for haemoglobin and myoglobin different?

A

The affinity of myoglobin to oxygen is constant despite the partial pressure of oxygen changing so the oxygen dissociation is hyperbolic.

However, the affinity of haemoglobin to oxygen is not constant because it has low affinity at low partial pressures and high affinity at high partial pressures. Therefore, the oxygen dissociation curve for haemoglobin is sigmoidal.

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14
Q

Describe the haemoglobin structure

A
  • made of 4 polypeptide chains - 2 alpha, 2 beta in a2b2 tetramer
  • Each chain contains an essential haem prosthetic group
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15
Q

Describe the structural change in haemoglobin as oxygen binds

A

Deoxyhaemoglobin can exist in low affinity T state or high affinity R state. In the T state, there are lots of ionic interactions between charged amino acid residues. Oxygen binding promotes stabilisation of the R state. The conformational change from T state to R state causes movement of the haem group as well as other amino acids so that the haem groups are more exposed.

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16
Q

Why is the oxygen dissociation curve for haemoglobin sigmoidal?

A

There is Cooperative’ binding of oxygen to haemoglobin.
The binding of one oxygen molecule promotes the binding of subsequent molecules as it changes to R state. Thus, there is a transition from low to high affinity state.

The sigmoidal binding curve of haemoglobin means that O2 efficiently loaded in the lungs and dissociated in the tissues.

17
Q

What 4 things can regulate oxygen binding to haemoglobin?

A
  1. 2,3 Bisphosphoglycerate (BPG)
  2. CO2
  3. H+
  4. Carbon monoxide
18
Q

How does 2,3-Bisphosphoglycerate (BPG) regulate oxygen binding?

A

1 BPG binds per haemoglobin tetramer and decreases the

affinity for O

19
Q

Where is BPG found?

A

In RBC

20
Q

How does BPG concentration change depending on altitudes?

A

BPG concentration increases at

high altitudes, promoting O2 release at the tissues.

21
Q

How does CO2 and H+ regulate oxygen binding?

A

H+ and CO2 can both bind to haemoglobin molecules.
Binding of H+ and CO2 lowers the affinity of haemoglobin for oxygen.
The BOHR EFFECT

22
Q

Why does myoglobin not exhibit the Bohr effect?

A

Myoglobin does not exhibit the Bohr affect because its made of a single polypeptide change so binding of CO2 or H+ does not result in a conformational change of sub units into the t or s state

23
Q

Why is the Bohr effect important?

A

Metabolically active tissues produce large amounts of H+ and CO2. The Bohr effect ensures the delivery of O2 is coupled to demand.

24
Q

What are the aim types of haemoglobin?

A

HbA -major haemoglobin found in adults
HbF - major haemoglobin found in fetus
HbA2 - Minor haemoglobin found in adults
HbA1C - formed by glycosylation of HbA

25
Q

Why is it that in the foetus, the major haemoglobin is HbF?

A

HbF has a Higher binding affinity for O2 than HbA which allows transfer of O2 to foetal blood supply from the mother.

26
Q

Which direction is the oxygen dissociation curve shifted to in HBF compared to HbA?

A

To the left

27
Q

What causes sickle cell anaemia?

A

Mutation of Glutamate to Valine in b globin (haemoglobin in individuals with sickle cell anaemia is called HbS). The glutamate is a hydrophilic negatively charged amino acid whereas the valine is hydrophobic. Because the valine is hydrophobic, it wants to eliminate contact with water so brings two affected haemoglobin molecules together
“Sticky” hydrophobic pocket formed by Val allows deoxygenated
HbS to polymerise. This aggregation leads to deformation of the red blood cell into a sickle-like shape making it relatively inflexible and unable to traverse the capillary beds.

28
Q

What are Thalassaemias?

A

Thalassaemias are a group of genetic disorders where there is an imbalance between the number of a- and b-
globin chains

29
Q

What causes b-thalassaemias?

A

decreased or absent b-globin chain production.

a- chains unable to form stable tetramers

30
Q

What causes a-thalassaemias?

A
  • decreased or absent a-globin chain production
  • several different levels of severity due to the multiple copies of the a-chains present
  • b-chains can form stable tetramers with increased affinity for oxygen
31
Q

When do the symptoms of a and b thalessaemias appear?

A

B - symptoms appear after birth

A - onset before birth

32
Q

What is the structural difference of HbA and HbF?

A

HbA is made of two alpha and two beta subunits whereas HbF is made of two alpha and two gamma subunits

Semester 1 - MCBG (18 decks)

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