Term
true or false?
Hb exists as a tetramer ie it is a multimeric protein? |
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Definition
this is true.
in contrast Mb is a monomeric protein |
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Term
human Hb is a tetrameric protein with an Mr of 64.4 kDa.
what do the four subunits that make up Hb each contain? |
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Definition
they contain a haem group with its Fe(II)
tetrameric Hb can combine reversibly with 4 O2 moelcules |
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Term
| normal adult Hb has two identical alpha chains and two identical..... |
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Definition
beta chains
the a2,b2 subunits are packed in a tetrahedral array. |
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Term
| the alpha and beta chains of Hb closeley resemble Mb but what is a notable stuctural dfference? |
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Definition
| Mb carries charged amino acids at positions which are hydrophobic in Hb and which are important in bonding the Hb subunits together |
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Term
| the dimers a1,b1 and a2,b2, are the to stable units that make up Hb. how many amino acids make up each alpha chain? |
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Definition
141
the beta chains are made up of 146 amino acids in each beta chain. |
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Term
| which waste product extreted in our urin can dissolve Hb into two ab dimers? |
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Definition
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Term
true or false?
there is no contact between the alpha chains in Hb? |
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Definition
False.. there is little contact between the alpha chains. However there is NO contact between the Beta chains
also there are strong contacts between the a1,b1 and the a1,b2 dimer. |
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Term
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Definition
allosteric interactions change the functionality of a protein allowing it to bind to something else.
allosteric regulators do not bind the site of interest themselves but to a remote site which in turn allows binding of the target molecule at the active site. |
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Term
| the wikipedia definition of allostery... |
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Definition
| allosteric regulation is the regulation of an enzyme or otherprotein by binding an effector molecule at the protein's allosteric site (that is, a site other than the protein's active site). Effectors that enhance the protein's activity are referred to as allosteric activators, whereas those that decrease the protein's activity are called allosteric inhibitors. |
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Term
| as well as O2, what two other things does hb transport? |
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Definition
H+ and CO2
Hb-O2 binding is regulated by three molecules
H+, CO2 and Biphosophoglycerate (2,3 BPG) |
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Term
| which three molecules relugate the binding of Hb to O2? |
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Definition
H+, CO2, Biphosphoglycerate 2,3 BPG
these regulatory molecules affect o2 binding despite being bound to sites distant from the haem. such interactions between spatially distinct sites are called allosteric interaction |
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Term
| where do H+, CO2 and 2,3 BPG come from and what affect do they have on Hb? |
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Definition
H+ come from active muscles
CO2 is a product of respiration
and 2,3 BPG is a product of glycolysis
these reduce the strength at which Hb binds O2 so forces it to give up its oxygen |
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Term
| at which PP will you find 50% of Mb have given up their oxygen? what curve does Mb-O2 binding have? |
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Definition
2.75 mm Hg (Torr)
the saturation curve of Mb-O2 binding has a hyperbolic shape. |
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Term
| how would you describe the binding between Hb and Oxygen? which binds oxygen tighter Mb or Hb? |
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Definition
Hb to O2 binding is cooperative. this means the binding of one oxygen molecule makes the binding of the second molecule easier, and so on with the thirds... a bit like postage and packing discount for every other item you buy in one order from ebay.
Mb binds tighter than Hb... tight tight tight yo! |
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Term
| true or false Hb-O2 binding has a hyperbolic shape? |
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Definition
false
Mb-O2 binding has a hyperbolic saturation curve.
Hb-O2 binding has a sigmoidal shape |
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Term
| what does the sigmoidal shape of Hb-O2 binding mean? |
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Definition
it means that Hb-O2 binding is positively cooperative and the binding of one oxygen faciliates the binding of progressive oxygen molecules.
eg the energy required to bind the 4th o2 molecule is less than that for the 3rd which is less than that for the 2nd. the first o2 molecule that binds will require the most energy. |
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Term
| the binding of o2 at one haem e..... the binding of o2 to other haems. this is positive c...... Cooperative binding makes Hb a more e........... transporter so it can d......... twice as much o...... as it would if the sites were independant. |
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Definition
| enhances, cooperativity, efficient, deliver, oxygen |
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Term
| what is the PP of Hb in RBC? this is where 50% Hb has given up its oxygen |
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Definition
26.6 mm Hg (Torr)
compare this to Mb 2.75 mm Hg (Torr), it binds O2 an order of magnitude more tightly than Hb. |
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Term
| describe the bonding of Hb to oxygen in the absence of the regulators H+, CO2 and 2,3 BPG... |
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Definition
in the absence of regulators, Hb binds o2 too tightly for physiological needs. the PP for pure Hb is:
P50 =2-5 mm Hg (more like Mb)
the regulators each weaken oxygen affinity to enable Hb to unload oxygen better. |
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Term
| in exercising mucsles l.....a..... is formed (cramp) and there is a.......... of venous blood from the d.......... of CO2 and its subsequent ionisation thus [H+] r............ |
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Definition
lactic acid, acidification, dissolution, rises
at these acidic condtions the oxygen dissociation curve shifts to the right and more O2 is released.
increased acidity enables the delivery of more oxygen without a fall of oxygen tension. |
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Term
| which amino acids are involved in binding protons? |
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Definition
the C-terminal His 146 on the beta chains
the pKa of the side-chain in free Histidine is 6.0 so this is one of the few amino acids capable of taking up protons at physiological pHs. |
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Term
where do protons bind to on Hb?
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Definition
protons bind c-terminal on His 146 on beta chains
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Term
CO2 produced by aerobic metabolism is mostly trasnported as bicarbonate.
write the equation for this. some CO2 reacts with which part of the Hb to form carbamates?
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Definition
CO2 +H20 <> HCO3- + H+
in addition, some CO2 reacts with the N terminal of alpha amino groups to form carbamates. |
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Term
true or false.
CO2 is both transported on Hb and acts as an allosteric regulator. |
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Definition
True
it reduces the oxygen affinity to Hb forcing it to give up its oxygen. it also reacts with the N terminal of alpha amino groups to form carbamates |
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Term
| where is 2,3 BPG produced? |
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Definition
in the RBC
it is produced from glycolysis in ceoncentrations of 4-5 mm... the same as Hb. |
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Term
| which form of Hb does 2,3 BPG bind to? deoxyHb or oxyHb or both? |
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Definition
it binds ONLY to deoxyHb with one molecule of BPG between the two subunits of Hb.
it is held electrostatically and causes Hb to release its oxygen. |
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Term
| what affect does BPG have on the oxygen dissociation curve? |
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Definition
it displaces it to the right thus weakening oxygen affinity
BPG is physiologically important because in its absence Hb would unload little oxygen in passing through the tissue capillaries, because the pO2 there is about 26 mm Hg. |
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Term
| out of Foetal Hb, Mb and adult Hb list them in order of their affinity to O2 starting with the strongest |
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Definition
Mb binds the tightest
Foetal Hb second tighest as baby must get oxygen from mother thus needs higher affinity to be able to get it from the mother
Adult Hb binds the least tighest out of all. |
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Term
| does an increase in temperature have any affect on the oxygen dissociation curve? |
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Definition
| yes it does, > in temperature causes the curve to shift to the right increasing the release of O2 eg in active muscles. |
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Term
Hb is composed of ..... subunits similar to structure of Mb. it binds 4 o2 molecules in a positively ............ manner. oxygen binding is affect by three allosteric regulators:-
............
.........
..........
these are produced by active muscles. |
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Definition
| four, cooperative, H+, CO2, 2,3 BPG |
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