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What is the primary function of hemoglobin?
How many heme groups are present in a hemoglobin molecule?
Which amino acid residue in hemoglobin is critical for binding to the iron atom in the heme group?
What is the approximate number of amino acids in the α-chain of hemoglobin?
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Which statement correctly differentiates fetal hemoglobin from adult hemoglobin?
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What component is NOT part of hemoglobin's structure?
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Which of the following factors DOES NOT affect hemoglobin function?
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In hemoglobin structure, how many globin polypeptide chains are present?
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What role does globin play in hemoglobin function?
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What structural configuration does hemoglobin have?
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Which statement correctly describes the relationship between oxygen binding and hemoglobin's structure?
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What happens to the iron atom when oxygen binds to hemoglobin?
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How does hemoglobin behave at low oxygen pressures?
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Which form of hemoglobin is referred to as the taut state?
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What type of bonds link the dimers in the hemoglobin structure?
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What is the significance of hemoglobin acting as a buffer in erythrocytes?
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What happens to hemoglobin's affinity for O2 in tissues with high CO2 levels?
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Which subunit is present in fetal hemoglobin that is not in adult hemoglobin?
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What is the effect of 2,3-BPG on fetal hemoglobin compared to adult hemoglobin?
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What is the primary role of carbaminohemoglobin (HbCO2)?
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What is the state of hemoglobin favored in the lungs with low CO2 levels?
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What is the shape of the oxygen dissociation curve for hemoglobin?
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What factor decreases the affinity of deoxygenated hemoglobin for oxygen?
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What is the effect called that describes the impact of pH on hemoglobin's oxygen binding?
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Which condition promotes the tighter binding of oxygen to hemoglobin?
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How does carbon monoxide (CO) affect hemoglobin's function?
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What is the role of 2,3-bisphosphoglycerate (BPG) in red blood cells?
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What is indicated by the steep upward curve in the oxygen dissociation graph near 20 to 30 mmHg?
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What stabilizes the T state of hemoglobin?
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What happens to the binding affinity of hemoglobin for oxygen in the presence of higher carbon dioxide levels?
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Which reaction does carbonic anhydrase catalyze in red blood cells?
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What is produced when carbonic acid dissociates?
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How does an increase in pH affect hemoglobin's oxygen binding?
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What form does hemoglobin carry carbon dioxide back to the lungs?
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What effect does carbon monoxide have on hemoglobin?
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What medical treatment is commonly used for carbon monoxide poisoning?
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What occurs when CO2 levels decrease in the lungs?
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Study Notes
Hemoglobin Structure
- A globular protein (hemoprotein) found in the cytoplasm of erythrocytes
- Primary function is to transport O2 and CO2 between the lungs and tissues
- Normal values:
- Fetus (just before birth): 16.5 to 18.5 gm/dl
- Fetus (end of 1 year): 12.5 gm/dl
- Adult male: 14-18 gm/dl
- Adult female: 12-15.5 gm/dl
- Composed of 4 heme groups and 4 globin polypeptide chains (1 heme/ 1 chain)
- Each globin subunit contains a heme-binding pocket
- Two important histidine residues (His) have a major role in hemoglobin function:
- Proximal histidine residue in the F helix of the globin chain [His F8] that binds to the 5th coordination site of Fe2+
- Distal histidine in the E helix [His E7] that stabilizes oxygen binding
- The α -chain contains 141 amino acids and β-chain (δ or chains) contains 146 amino acids.
- The secondary structure of all globin chain types is formed of 8 α helices identified by the letters A to H.
- The tertiary folding of each globin chain forms an approximate sphere.
Hemoglobin Function
- Hb is an important buffer in the erythrocytes and blood.
- Hb is a carrier of O2 and CO2
- Hb binds O2 weakly at low oxygen pressures and tightly at high pressures.
- The binding of the first O2 to Hb enhances the binding of further O2 molecules.
- Hb exists in 2 different forms: T-form (T = tense) and R-form (R= Relaxed).
- Oxygenation rotates the 11 dimer in relation to 22 dimer about 15°.
- Hb changes from the T → R states.
- The Fe is about 0.6 Å out of the heme plane in the deoxy state.
- When oxygen binds, it pulls the Fe back into the heme plane.
- Oxygenation of one hemoglobin molecule produces rupture of some week noncovalent hydrogen and ionic bonds and rotation of one dimer ()1 15 degrees relative to the other dimer ()2.
Factors Affecting Hemoglobin Function
- Oxygen
- The oxygen dissociation curve for hemoglobin is sigmoidal in shape, indicating that the subunits cooperate in binding oxygen.
- This effect is referred to as heme-heme interaction.
- 2,3-bisphosphoglycerate (BPG)
- A three-carbon molecule formed during glycolysis
- Formed in human red blood cells
- 2,3 BPG binds with greater affinity to deoxygenated hemoglobin decreasing their affinity for oxygen.
- This enhances the ability of RBCs to release oxygen near the tissues.
- pH [H+ and CO2]
- High pH (low [H+] or alkaline) promotes tighter binding of oxygen to hemoglobin.
- Low pH (high [H+] or acidic) permits the easier release of oxygen from hemoglobin.
- The effect of pH on the oxygen binding ability to Hb is called the Bohr effect.
- The Bohr effect is the reciprocal coupling of protons and O2 binding to Hb.
- Also, it explains why red blood cells unload oxygen in tissues.
- Carbon monoxide (CO)
- CO binds tightly to the hemoglobin iron, forming carboxyhemoglobin (HbCO).
- When CO binds to one or more of the four heme sites, Hb shifts to the relaxed conformation, which causes the remaining heme sites to bind oxygen with high affinity.
- As a result, the affected hemoglobin is unable to release oxygen to the tissues.
- The affinity of hemoglobin for CO is about 200 times greater than for oxygen.
- Carbon monoxide poisoning is treated with 100 percent oxygen therapy, which facilitates the dissociation of CO from hemoglobin.
Fetal Hemoglobin (Hb F)
- Has a different subunit (than the β subunit of the adult hemoglobin) called a γ subunit or α2γ2.
- The γ chain differs from the chain β in that, there is a change in a single amino acid found in the 2,3-BPG 'binding pocket': from Histidine to serine.
- 2,3 BPG binds less well to HbF than to HbA.
- This gives HbF a higher affinity for O2 than HbA.
- In Fetal hemoglobin, BPG does not affect O2 binding and the baby’s blood will get its oxygen from the mother’s hemoglobin.
- The transfer of oxygen is from the mother (less tightly bonded) to the baby (more tightly bonded).
Hemoglobin Derivatives
- Oxyhemoglobin (oxyHb) = Hb with O2
- Deoxyhemoglobin (deoxyHb) = Hb without O2
- Carbaminohemoglobin (HbCO2) - CO2 is non-covalently bound to globin chain of Hb. HbCO2 transports CO2 in blood.
- Carboxyhemoglobin (HbCO) – carbon monoxide (CO) binds to Fe2+ in heme in case of CO poisoning or smoking. CO has more than 200x higher affinity to Fe2+ than O2.
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Description
Explore the intricate structure of hemoglobin, a vital globular protein crucial for oxygen and carbon dioxide transport in the body. This quiz covers hemoglobin's composition, normal values across different life stages, and the specific roles of histidine residues in its function.
