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How do the arterial and venous partial pressures of oxygen change during exercise compared to rest? Why?
Arterial partial pressure does not change much (100mmHg). Venous partial pressure of oxygen during exercise (20mmHg) decreases from during rest (40mmHg). This is because during exercise, peripheral tissue is utilizing more oxygen. Since Hb displays cooperativity, it releases more oxygen when the partial pressure is low (during exercise) when the muscles need it the most.
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What is physiological pH?
Physiological pH = 7.4
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How is CO2 carried in the blood?
13% of CO2 is carried by Hemoglobin (carbamylation of the N-terminal amino group of globin chains); 87% of CO2 is dissovled in blood
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What percent of the O2 shift is due to CO2 vs. H+ (change in pH)?
75% of the O2 shift is due to H+; 25% of the O2 shift is due to CO2 modification of Hb (carbamylation of N-terminal amino groups of globin chains).
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Describe the mechanism of the Bohr affect. What is Bohr his? HOw does this change the pKa, affinity for H+, and acid strength of deoxyHb?
Following conformational change upon deoxygenation, three residues of Hb are in a more (-) environment. These are HIS 146 (Bohr HIS), HIS 122, and alpha amino group of the alpha chain. This increase the pKa of Hb, increases the affinity of H+, and makes deoxy Hb and weaker acid.
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Where does 2,3-BPG bind on the deoxyHb?
One BPG molecule binds the center of a Hb tetramer. Typically binds 3 residues on each beta globin. HIS 143; LYS 82; HIS 2
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Why does HbF have a lower affinity for BPG than deoxy HbA? How is this beneficial?
Basically HbF has a higher affinity for O2 than HbA. HbF has gamma globin instead of beta globin. Gamma globin has a SER 143 instead of HIS 143, therefore it binds BPG less strongly. This lower affinity for BPG translates to a higher affinity for Oxygen. This is beneficial since HbF typically has to obtain oxygen from HbA in circulation.
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What are the 5 regulators of Hb? How do they change the affinity of Hb for O2? Which way does the curve shift?
All 5 regulators decrease the affinity of HbA for O2 and the curve shifts to the right. Regulators: 1. [H+]; 2. CO2; 3. BPG; 4. Cl-; 5 increase in Temperature
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What is the metabolic source of BPG? When do BPG levels increase? When is BPG lost? How can BPG be maintain in solution to replicate physiological conditions?
BPG is a metabolic by product of glycolysis. BPG levels increase during anemia or hypoxia (increase in altitude). BPG is lost in solution when stored in citrate-glucose. BPG can be maintained with inosine via ribose
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Severe Anemia. What occurs to the curve and why?
Curve shifts to the right due to BPG compensation. 3.3/4.5 = 73% efficient
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What role does distal HIS E7 have in CO binding? HOw does this affect the affinity of CO compared to O2?
Prevents CO from binding in linear conformation (like it normally would to heme groups). Forces the bent conformation. However Hb still has a higher affinity for Co than for O2.
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What reaction does metHB reductase catalyze? What other molecule is required?
NADH is required. Coverts metHb(Fe3+) to Hb(Fe2+)
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What are sulfonamides?
drug that oxidizes Hb(Fe2+) to MetHb
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Familial MetHemoglobinemia
hereditary absense of metHB reductase
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Genetic substitution of proximal HIS (F8) or distal HIS (E7) for Tyr
Also converts Hb to metHb(Fe3+)
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How does HbAS (hetero for sickle cell) protect against malaria?
HbAS with malaria infection forms knobs which stick to the endothelium and are cleared from circulation.
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What specific mutation occurs in sickle cell anemia?
GLU (E6) to Val on beta globin chain. This is a change of a negatively charged a.a. to a hydrophobic a.a.
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What are some treatment options of sickle cell?
hydroxyurea, gene therapy, bone marrow transplant, 5-azacytidine (increases HbF in adults - gamma globin has no mutation so no affect)
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What physiological processes can increase daily iron requirement?
puberty/growth, menstruation, pregnancy, lactation
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Transferrin
serum Fe3+ transport protein. Circulate iron from liver to bone marrow/muscle/tissues to RBCs.
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Transferrin Receptors
cellular uptake of iron via clathrin coated pits.
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Ferritin. How much iron can one molecule of Ferritin carry?
cellular iron storage, Ferritin holds 4500 iron molecules and is 23% iron by weight.
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Hemosiderin
denatured insoluble iron
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Ferrochelatase
enzyme that catalyzes insertion of iron into porphyrin to make heme
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What is the major cause of Anemia?
inssuficient iron in the diet
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Primary Hemochromatosis
Hereditary overload of iron; Homo mutation for C260Y
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Secondary Hemochromatosis
overload of iron possible due to blood transfusion. can lead to many other diseases. Increase lipid oxidation
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How can Hemochromatosis be measured?
Measure the sat of transferrin. Check to see it is over 40%
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What is normal iron excretion per day? How?
1.0mg per day; excretion in the urine, GI bleeding, shedding, sweat
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What is the total iron in body? Where is it stored?
3.5grams total; stored in ferritin and hemisiderin
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HbH
alpha thalassemia with (beta4). Occurs when 3 defective alpha genes
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HbBart's; AKA?
alpha thalassemia with (gamma4). Occurs when all 4 alpha genes are defective; hydrops fetalis
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Thalassemias
alpha or beta chains missing or depleted
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beta Thalassemia has 2 main forms. What are they?
1. NOn deletion form: single bp change; 2. Deletion form: beta 0, HPFH-1, lepore, kenyaa, delta beta
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HPFH-1
beta thalassemia disease where beta chain is completely gone. However gamma chain takes over so individual has HbF and functions normally.
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How does conformation of Hb change from T(deoxy) state to the R(oxy) state? Explain large scale and small scale changes.
Large scale: a1B1 dimer rotates 15 degrees or 0.8 angstroms with respect to a2B2; Small scale: When oxygen binds Fe2+, it decreases the diameter of the iron molecule. This pulls Fe2+ into the plane of the heme group (protoporphyrin IX) and subsequently pulls the proximal HIS F8 as well.
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