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HemoglobinBiochem
UMDNJSOM
| Question | Answer |
|---|---|
| Hemoglobin molecule | 4 polypeptide subunits(globin chains) and 4 heme groups (one heme on each globin) |
| HbA | Two alpha chains, two beta chains |
| Iron atom | In heme. responsible for reversible binding of oxygen molecule. can only bind in Ferrous(fe2+). Oxygen binds reversibly to Fe2+ without causing oxidation due to hydrophobic character of heme binding pocket. |
| Methemoglobin | Ferric(Fe3+). heme does not bind oxygen. |
| Iron atom is coordinated to | Histidine called HisF8. and by porphyrin N atoms(4 of them) |
| Heme | Protoporphyrin ring with iron. Four pyrrole groups linked by methane bridges. |
| Iron positioning in plane | Deoxyhemoglobin - Iron is out of plane. Iron=tetrahedral pyramidal Oxyhemoglobin - O forms 6th coordination partner. now octahedral. Iron is in the plane of the porphyrin ring. |
| Relaxed State | Oxyhemoglobin. Favors oxygen binding. Bind O2, change in Conf State. involves breaking+forming salt bridges. Take O2, 2 B chains move closer. |
| Iron atom moving into porphyrin plane | upon oxygenation of heme group. his residue(attached to iron) drawn closer to heme. shifts AA nearby. interface between 4 subunits altered. 1 heme oxygenated, whole protein changes. Now, easier for other 3 heme to become oxygenated. |
| Cooperative Binding | binding of one molecule of O2 to hemoglobin enhances ability of hemoglobin to bind more O2 molecules. Example of an ALLOSTERIC EFFECT. |
| Tense State | Deoxyhemoglobin. Lower binding affinity for oxygen. |
| Oxygen Saturation Curve of Hemoglobin | Sigmoidal. As PaO2 increases, so does binding to oxygen, and vice versa. Sigmoidal is result of the cooperative binding of oxygen. |
| Oxygen biding of myoglobin vs hemoglobin | myoglobin binds O2 under conditions where hemoglobin releases it, below 20 Torr in muscle. |
| Oxygen saturation curve of myoglobin | Hyperbolic due to Non cooperativity |
| signifiance of sigmoidal oxygen binding curve. | Only hemoglobin will release O2 at the PaO2 present in tissues. Then Mb can take it up. |
| P50 | Partial pressure at which hemoglobin is 50% bound. 26.6 mmHg |
| What causes a left shift in the oxygen binding curve?(higher affinity) | Low temp, Low 2,3-BPG, low p(CO2), high p(CO), high pH, Hbf. |
| What causes a right shift in the oxygen binding curve? (lower affinity) | high temp, high 2,3-BPG, high p(CO2), low p(CO), low pH, Hba. |
| Haldane Effect | Deoxygenated Hb has greater affinity for CO2 than does oxyHb. O2 release facilitiates CO2 pickup, vice versa. |
| Bohr Effect | Deoxygenated Hb has greater affinity for H+ than does oxyhemoglobin. Presence of CO2 gives rise to release of O2 from Hb. |
| Bohr Effect Biochemical Basis | 1) High [CO2] lowers pH. Co2+H2O=H+ +HCO3. These protons bind Hb, reduces its affinity for O2, stabilize T state. Depends on salt bridge formation by presence of added proton on histidine B146.AND Co2+terminalamino=carbamate, stabilize deoxyHb |
| Bohr effect and acid conditions | pH 7.4 to 7.2, in lungs(pO2=100), no effect. In tissue(pO2=40), %sat goes from 70% to 60%. lower pH, release oxygen, T state favor. |
| Bohr effect significance | Lower pH will cause Hb to deliver more oxygen in active tissue. creates more Co2, lowers pH. important in exercise. |
| temperature effect | increasing temperature, denatures bond between oxygen and hemoglobin. Increases amt of O2 and Hb. Decreases OxyHb. Decreased temp, increased affinity. important during hypothermia. |
| 2,3 BPG effect | Stabilizes T conformation. Reduces affinity for O2. Binds central cavity of deoxyHb. Interacts with 3 positivel charged groups, histidine 143, lysine 82, histidine 2) on each beta chain. On T-R, pocket collapses, 2,3 BPG released. |
| 2,3 BPG as allosteric effector | It is an allosteric effector of hemoglobin's affinity for O2. Shifts oxygen curve to right. |
| Why is increased 2,3 BPG helpful when oxygen supply is low? | Because it helps to release oxygen to tissues easier. |
| Carbon Monoxide | Hb binds with CO 200x more readily than with oxygen. Also shifts curve to the left. Presence of one CO causes O2 to bind with more affinity. cooperative binding. |
| Carbon monoxide poisoning | colorless, odorless, tasteless, byproduct of combustion. small enough to fit into Hb crevice, bond is so strong, irreversible. person rapidly dies of asphyxiation. Co+HB = Carboxyhemoglobin. bright red. t1/2= 5 hrs. |
| Hydrogen cyanide poisoning | binds irreversibly to iron atom in Hb. make it unavailable to transport O2. binds to Hb, taken to tissues, binds to Cytochrome oxidase in mitochrondria. interferes with Oxidative phosphorlyation, death. usually gas. can be fruits+vegs too. |
| Fetal hemoglobin | Higher affinity for oxygen than HbA. p50 of HbF = 19. p50 of HbA = 26.6. Tetramer, contains two alpha and two gamma globin chains. gamma globin chains have low affinity for 2,3 BPG. Curve shifts left. |
| Gamma globin chain and 2,3 BPG | His143, involved in binding 2,3BPG to B subunit, replaced by Ser 143. removes two positive charges from 2,3BPG binding site. Reduced affinity for BPG. |
| High altitude Adaptation | Increase # of erythrocytes, increase Hb contet/cell and increased synthesis and circulatory level of BPG Within 24 hours, increase BPG. Increased BPG, reduced affinity for O2 by Hb, released into tissue, increased efficiency. |
Created by:
nady
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