Term
| myoglobin Mb and haemoglobin Hb are two alpha domain proteins. where do they function? |
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Definition
Mb - intracellular oxygen transport
Hb - oxygen transport in the blood
Earths atmosphere contains 20.95% oxygen by volume. the concentration of Oxygen is described by its partial pressure |
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Term
| at 20C and relative humidity of 50%, water vapour pressure is 17.5 mm Hg (Torr) How is the partial pressure of oxygen calculated? |
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Definition
pO2 = (760-17.5) x 20.95/100 = 155.5 mm Hg (Torr)
this is the typical concentration available for us to breathe! |
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Term
| the partial pressure (PP) is further l........ by the time oxygen is in the alveoli. in humans m....... facilitates the d....... of oxygen. |
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Definition
lowered, myoglobin, difussion
Hb = alveolus, artery, capillaries
Hb - Mb = interstitial fluid
Mb = cytosol, vein, mitochondria |
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Term
true or false?
Mb serves as Hb in whales? |
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Definition
| this is true. Mb was first purified from whale blood in 1958 by Max Perutz. |
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Term
| how many aa does Mb have? what is its Mr? what percentage of it contains alpha helical folds? |
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Definition
155 amino acids
~ 17 kDa
75% alpha helical fold
the interior of the molecule consists almost entirely of non-polar residues |
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Term
| where is the haem group located in Mb? what is it surrounded by? What are the two exceptions? |
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Definition
heam group located in crevice
it is surrounded by non-polar residues except for two histidines
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Term
Mb is a p....... derived from m...... About 75% of the main chain is f.... into RH alpha helices referred to as ABCDEFH
what are the helical segments generally terminated by? |
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Definition
protein, muscle, folded
helical segments generally termiated by Proline residues. Proline is a cyclic aa with a locked conformation angle thus cannot adopt the conformation required for an alpha helix. |
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Term
| binding of O2 to a free haem group is irreversible. enclosure in a protein allows reversible binding. O2 has limited solubility in water 1 x 10-4 M. How is this solubility problem overcome? |
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Definition
By binding to proteins. This also increases diffusion.
Binding of o2 alters haem structure and causes change in the haem electronic spectrum that we can see. Bright scarlet color of blood in arteries (o2 bound) and Dark purple colour of blood in veins (o2 unbound) |
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Term
haem is a non-polypeptide group. it confers oxygen binding capacity on Mb and Hb and gives them their colour.
what atomand organic part does the Haem group contain? |
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Definition
an iron atom Fe(II) and an organic part protoporphyin IX. these occur in both Mb and Hb.
the Fe(II) in haem binds to 4 Nitrogen atoms in a plane but has two other coordination positions on either side of the haem plane..the 5th and the 6th coordination postions |
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Term
| which state of the iron atom can bind oxygen? |
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Definition
ONLY the Fe(II) state can bind Oxygen not the Fe(I) nor Fe and neither Fe(III)
in Mb and Hb the haem group contains an iron Fe(II) atom and a IX protoporphyin |
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Term
| two key histidines in helices E and F are so called what? |
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Definition
Distal Histidine E7
Proximal Histidine F8
the iron atom of the haem is directly bonded to the proximal F8 histidine. this occupies the 5th coordination position. this bonding cause the iron atom to be slighly out of plane of the porphyrin on this side of the histidine by 0.3A |
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Term
the iron atom of the haem is directly bonded to the proximal F8 histidine. this occupies the 5th coordination position.
what does this bonding cause? |
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Definition
| this bonding causes the iron atom to be slighly out of plane of the porphyrin on this side of the histidine by 0.3A |
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Term
| out of the 6 coordination positions 4 are taken by nitrogen, 1 by the proximal F8 hisitidine and the 6th position by whom? |
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Definition
the distal E7 histidine. it has two roles
- it reduces the affinity of binding carbon monoxide (CO) for the site, which still remains higher that that for oxygen
- it sterically blocks the formation of Mb associates in which haem-o2-haem sandwhiches would form.
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Term
CO binds in a linear structur to haem group tightly.
O2 binds in a bent structure less tightly.
How does the distal histidine E7 weaken the CO bond? |
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Definition
| it forces both CO and O2 to bind in a bent way. For O2 this is its normal way of binding. But for CO, it weakens its binding. Still, the affinity for binding carbon monoxide remains higher than that for oxygen |
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Term
in Mb -O2 binding, what shape does the saturation curve show?
what is the partial pressure at which 50% of Mb molecules have released their oxygen? |
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Definition
the saturation curve shows a hyperbolic shape
the PP at which 50% Mb have released their oxygen is 2.75 mm Hg (Torr) |
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Term
Mb inside muscle cells facilitates the diffusion of O2 by binding O2 when concentration is high at the interface with the extracellular fluid and releasing it where O2 concentrations is low (at the mitochondria)
in humans Mb facilitates the diffusion of oxygen but... |
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Definition
| In diving mammals, there is a special adaptation. eg Weddell seals can store oxygen in the myoglobin in their muscles |
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