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14 Cards in this Set
- Front
- Back
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*** In which human organ is myoglobin (Mb) most important? |
HEART |
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*** Explain the causes and importance of a right shift in the Hb/O2 binding curve. |
Causes of right shift in the Hb/O2 binding curve:
1. decreased pH (increased H)s 2. Increased CO2 [] 3. Increased 2,3-BPG 4. Increased Temperature
***Importance of a right shift in the Hb/02 binding curve.
-A right shift imporves oxygen delivery to capillaries in tissues, especially when there is a high tissue demand for oxygen
- A right shift is NOT important in the lungs (b/c you dont want to deliver/unload oxygen in the lungs, you want to retrieve/load the oxygen onto the RBCs)
-A right shift in the Hb/O2 binding curve is most important at pO2's near the P50.
-Theres an increase in the P50 when theres a right shift
-In a right shift, hemoglobins will be less saturated at PO2's near 25 torr. |
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***In Hb how does the binding of the first oxygen molecule affect the binding of the next ones? |
In Hb the binding of the first oxygen to one heme increases the affinity of the other hemes to the next oxygen
In myoglobin the binding of oxygen to heme has NO influence on the binding of oxygen to other hemes of Mb |
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*** What is the Bohr effect? |
Increased binding of H+ or CO2 to hemoglobin decreases the affinity of hemoglobin to oxygen, thus facilitating the unloading of oxygen in tissues.
It essentially IS the right shift |
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*** What is the physiological importance of cooperativity in Hb function? |
Coopertivity of Hb function represents O2 delivery. Oxygen deliver is greater in the molecules w/ greater cooperativity
*** cooperativity improves HB function by increasing its saturation at high PO2 and decreasing its saturation at low PO2 |
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***Compare the behavior of Mb and Hb w/ respect to O2, CO2 and H
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Myoglobin -Can bind to oxygen; Mb has only ONE O2 BINDING SITE, so it can ONLY bind ONE oxygen
Does NOT bind to CO2 nor H+, thus Mb cannot undergo the Bohr effect
Hb
-Has FOUR O2 Binding sites, so it can bind up to FOUR O2. -Can bind to BOTH CO2 and H+, Thus Hb can undergo the Bohr effect |
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***How does the protein (globin) portion of Mb or Hb affect the reactivity of heme? |
In Mb the heme is tucked into a pocket between domains E and F.
In Hb, the heme is tucked into a globin pocket formed by interactions between the four subunits. Tucking the heme inside these globin pockets will weaken the avidity of heme to oxygen. If heme is not tucked away, the naked heme will interact w/ oxygen very avidly to form superoxide free radical which is not good. (methemoglobin / metmyoglobin) |
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***How and where does 2,3-BPG interact w/ Hb? Where does 2,3-BPG come from |
2,3 BPG is synthesized from an intermediate of glycolysis.
2,3 BPG binds to deoxy Hb between the two eta subunits
2,3BPG has negative charges taht interacts w/ the positive charges on the beta subunits
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***How does fetal Hb (HbF) differ from HbA? |
Adult Hb have beta chains and beta chains interact w/ 2,3 BPG
Fetal hemoglobins have gamma chains instead of beta chains. W/out B chains fetal Hb are not affected by 2,3 BPG levels
Fetal Hb contains 2 Alpha chains and 2 GAMMA chains. Adult Hb contains 2 alpha chains and 2 beta chains |
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*** What does the Hill equation describe? |
n = coopertivity n can range from 1 to x (where x = #of subunits) n = 1 ; no coopertivity n>1 = positive coopertivity n<1 = negative coopertivity |
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***How does NO (nitric oxide) interact w/ Hb and what is the physiological significance of that interaction? Consider the many parts of this question |
Under low oxygen conditions, Hb can convert nitrite (NO2-) into Nitric oxide.
Hb can reversibly bind to NO, both at heme iron and at the cysteine residues in the globin chains.
physiological importance of Hb-NO interaction: Makes Hb an important mediator of vascular tone (because NO, is a potent vasodilator) |
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*** Notes about P50 |
P50 = the PO2 at which 50% of the binding sites are occupied
P50 for Hb is 26 torr
P50 for Mb is ~3 torr
The fractional saturation (Y) of myoglobin is less than Hb |
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***Properties of Heme (in both Hb and Mb) |
Attached to Mb or Hb via Histidine F8
Can bind to oxygen w/out being associated w/ protein (e.g. globin)
Synthesized in the body
Has Ferrous Iron (Fe2+) at its center |
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***What can Hb carry? |
1. Oxygen 2. CO2 3. Protons (H+) 4. Nitric Oxide (NO) |
