BCH4024 EXAM 1 PURICH QUESTIONS
WITH CORRECT ANSWERS (LATEST
2024-2025 UPDATES)
Similarities between Hb and Mb - Answer- -Both 8 helix polypeptides
-Have heme group between helices E and F
-Bind oxygen reversibly
-Only have 27 identical AAs but very similar structure
Heme - Answer- -binds the O2 (the hemoglobin does not bind to O2 respectively)
-found between E and F helices (found only in ONE particular place)
-heme molecules do NOT come into contact with one another, and O2 binding behavior
depends on subunit interactions
Hemoglobin basics????? - Answer- -α2β2 tetramer with 4 heme groups and 4 oxygen
binding sites
-Cooperative oxygen binding gives sigmoidal curve
-If treated with HgCl2, it will dissociate the subunits and the cooperativity is lost
Comparison of Mb and Hb Structures - Answer- -even though the 3 polypeptide chains
of Mb, a-Hb and B-Hb only share 27 identical residues, the structures are very similar
-illustrates principle that structural/functional similarity need not require extensive
sequence identity
-protein folding patterns are conserved during evolution!!!
Hemoglbin's O2 Binding Curve - Answer- -Hb is fully saturated at lung O2 pressure
-Hb dumps 2/3 of its O2 to peripheral tissues
-remaining O2 for higher physical activity
-the S-shaped curve results from COOPERATIVITY, meaning that Hb's subunit-subunit
interactions have altered the O2 saturation curve
-binding curve seems to suggest that binding to 1st site is weak, binding to 2nd site is
stronger, binding to 3rd site is stronger, etc. (however, there is NO change in affinity
with hemoglobin)
-pO2 is used because it was once difficult to determine the dissolved O2 conc.
However, Dalton proved that the conc. of a dissolved gas is always directly proportional
to the pressure of the gas in equilibrium with the liquid. Pressure is conveniently
measured
Myolglobin (monomer) - Answer- -buffers O2 conc. in muscle (ready reserve for short
periods)
-O2 saturation curve is hyperbolic
-higher affinity for O2 assures transfer from Hb(O2)4 to Mb
, -lower than peripheral tissue binding; if O2 is released and there is myoglboin nearby, it
will interact with the myoglobin (myoglobin and hemoglobin will never touch bc
myo=muscle; separated by 3 peripheral membranes)
-Monomer that has NO cooperativity- hyperbolic binding curve
Hemoglobin - Answer- -O2 binding is Cooperative
-α2β2 tetramer with 4 heme groups and 4 oxygen binding sites
-Cooperative oxygen binding gives sigmoidal curve
-If treated with HgCl2, it will dissociate subunits & cooperativity is ultimately lost (without
tetramer, there can be NO cooperativity)
-Hemoglobin is cooperative due to the subunit-subunit interactions
why is cooperativity life or death? (review the math equations and how to solve) -
Answer- -for us to survive, Hb must deliver 2/3 of its boundO2 to our peripheral tissues
on each pass
-recall the equation for noncooperative binding:
[Ptot]/[P.L]={1=Kd/[l]} (if we used myoglobin or noncooperative binding, out cells would
use this equation and we would DIE. (as soon as we use myoglobin to release 2/3 of
O2, we would require a low PO2 which would ultimately kill our tissues)
-ABSENT COOPERATIVITY--> WE WOULD DIE
Concerted Cooperativity Model (Monod Model) - Answer- -Hb occurs in two
conformationally constrained states: T-state & R-state
-there are no hybrid forms (none containing both T and R subunits); subunits change
shape in concert as they transition from T (square) to R (round)
-T-state (Hb-T) has little or no affinity for O2
-R-state (Hb-R) has good affinity for O2
-Tzero-state is greatly favored compared to Rzero-state, when there is NO bound O2.
-O2 binding stabilizes R-state, thereby inc population of Hb subunits in the R-state
Subunit Interactions constrain Oxygen Binding - Answer- -conformational changes are
transmitted across subunit-subunit interface, altering O2 binding to other hemes
Tzero can't bind O2 very well, but Rzero can. Why? - Answer- -O2 only binds when
Fe2+ is in the plane of heme ring.
-Tzero: Fe2+ is out of the plane of hemer ring and is found deep in the helix so O2 will
NOT bind
-Rzero: Fe2+ is in the plane of heme ring in R states so O2 will bind
-O2 stabilizes conformational change at His F8 that is transmitted through the peptide
backbone, changing the tertiary structure of the entire subunit
Two conformational states of Hb - Answer- -Tense State (T-state) is most stable in the
absence of oxygen and binds with low affinity
-Relaxed state (R-state) is stabilized by oxygen binding, binds with high affinity
-Histidines closes the hole in T-> R state transition
-When O2 binds the bound Fe2+ pulls the HisF8 towards the plane of the heme ring
WITH CORRECT ANSWERS (LATEST
2024-2025 UPDATES)
Similarities between Hb and Mb - Answer- -Both 8 helix polypeptides
-Have heme group between helices E and F
-Bind oxygen reversibly
-Only have 27 identical AAs but very similar structure
Heme - Answer- -binds the O2 (the hemoglobin does not bind to O2 respectively)
-found between E and F helices (found only in ONE particular place)
-heme molecules do NOT come into contact with one another, and O2 binding behavior
depends on subunit interactions
Hemoglobin basics????? - Answer- -α2β2 tetramer with 4 heme groups and 4 oxygen
binding sites
-Cooperative oxygen binding gives sigmoidal curve
-If treated with HgCl2, it will dissociate the subunits and the cooperativity is lost
Comparison of Mb and Hb Structures - Answer- -even though the 3 polypeptide chains
of Mb, a-Hb and B-Hb only share 27 identical residues, the structures are very similar
-illustrates principle that structural/functional similarity need not require extensive
sequence identity
-protein folding patterns are conserved during evolution!!!
Hemoglbin's O2 Binding Curve - Answer- -Hb is fully saturated at lung O2 pressure
-Hb dumps 2/3 of its O2 to peripheral tissues
-remaining O2 for higher physical activity
-the S-shaped curve results from COOPERATIVITY, meaning that Hb's subunit-subunit
interactions have altered the O2 saturation curve
-binding curve seems to suggest that binding to 1st site is weak, binding to 2nd site is
stronger, binding to 3rd site is stronger, etc. (however, there is NO change in affinity
with hemoglobin)
-pO2 is used because it was once difficult to determine the dissolved O2 conc.
However, Dalton proved that the conc. of a dissolved gas is always directly proportional
to the pressure of the gas in equilibrium with the liquid. Pressure is conveniently
measured
Myolglobin (monomer) - Answer- -buffers O2 conc. in muscle (ready reserve for short
periods)
-O2 saturation curve is hyperbolic
-higher affinity for O2 assures transfer from Hb(O2)4 to Mb
, -lower than peripheral tissue binding; if O2 is released and there is myoglboin nearby, it
will interact with the myoglobin (myoglobin and hemoglobin will never touch bc
myo=muscle; separated by 3 peripheral membranes)
-Monomer that has NO cooperativity- hyperbolic binding curve
Hemoglobin - Answer- -O2 binding is Cooperative
-α2β2 tetramer with 4 heme groups and 4 oxygen binding sites
-Cooperative oxygen binding gives sigmoidal curve
-If treated with HgCl2, it will dissociate subunits & cooperativity is ultimately lost (without
tetramer, there can be NO cooperativity)
-Hemoglobin is cooperative due to the subunit-subunit interactions
why is cooperativity life or death? (review the math equations and how to solve) -
Answer- -for us to survive, Hb must deliver 2/3 of its boundO2 to our peripheral tissues
on each pass
-recall the equation for noncooperative binding:
[Ptot]/[P.L]={1=Kd/[l]} (if we used myoglobin or noncooperative binding, out cells would
use this equation and we would DIE. (as soon as we use myoglobin to release 2/3 of
O2, we would require a low PO2 which would ultimately kill our tissues)
-ABSENT COOPERATIVITY--> WE WOULD DIE
Concerted Cooperativity Model (Monod Model) - Answer- -Hb occurs in two
conformationally constrained states: T-state & R-state
-there are no hybrid forms (none containing both T and R subunits); subunits change
shape in concert as they transition from T (square) to R (round)
-T-state (Hb-T) has little or no affinity for O2
-R-state (Hb-R) has good affinity for O2
-Tzero-state is greatly favored compared to Rzero-state, when there is NO bound O2.
-O2 binding stabilizes R-state, thereby inc population of Hb subunits in the R-state
Subunit Interactions constrain Oxygen Binding - Answer- -conformational changes are
transmitted across subunit-subunit interface, altering O2 binding to other hemes
Tzero can't bind O2 very well, but Rzero can. Why? - Answer- -O2 only binds when
Fe2+ is in the plane of heme ring.
-Tzero: Fe2+ is out of the plane of hemer ring and is found deep in the helix so O2 will
NOT bind
-Rzero: Fe2+ is in the plane of heme ring in R states so O2 will bind
-O2 stabilizes conformational change at His F8 that is transmitted through the peptide
backbone, changing the tertiary structure of the entire subunit
Two conformational states of Hb - Answer- -Tense State (T-state) is most stable in the
absence of oxygen and binds with low affinity
-Relaxed state (R-state) is stabilized by oxygen binding, binds with high affinity
-Histidines closes the hole in T-> R state transition
-When O2 binds the bound Fe2+ pulls the HisF8 towards the plane of the heme ring
