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A) how to explain that a venous blood looks purplish blue and an arterial blood appears bright red to us? B) what other important for life porphyrins (complex ions) do you know?

A) how to explain that a venous blood looks purplish blue and an arterial blood appears bright red to us? B) what other important for life porphyrins (complex ions) do you know?

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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A) how to explain that a venous blood looks purplish blue and an arterial blood appears bright red to us? B) what other important for life porphyrins (complex ions) do you know?
Complex ions in Living systems Despite the structural complexity of biomolecules, the principles of bonding and d-orbital splitting are the same as in simple inorganic systems. In this discussion we focus on iron. Iron plays a crucial role in oxygen transport in all vertebrates. The oxygen-transporting protein hemoglobin consists of four folded protein chains called globins, each cradling the iron-containing complex heme. Heme is a porphyrin, a complex derived from a metal ion and tetradentate ring ligand known as porphin. Iron (II) is centered in the plane of the porphin ring, forming coordinate covalent bonds with four N lone pairs, resulting in a square planar complex. When heme is bound in hemoglobin, the complex is octahedral, with the fifth ligand of iron (II) being an N atom from a nearby amino acid (histidine), and the sixth an O atom from either an O, (shown) or an H,0 molecule. Hemoglobin exists in two forms, depending on the nature of the sixth ligand. In the blood vessels of the lungs, where O2 concentration is high, heme binds 0, to form oxyhemoglobin, which is transported in the arteries to 0,-depleted tissues. At these tissues, the O, is released and replaced by H,0 molecule to form deoxyhemoglobin, which is transported in the veins back to the lungs. The H,O is a weak-field ligand, so the d ion Fe2* in deoxyhemoglobin is part of a high-spin complex. Because of the relatively small d-orbital splitting, deoxyhemoglobin absorbs light at the red (low-energy) end of the spectrum and looks purplish blue, which accounts for the dark color of venous blood. On the other hand, O2 is a strong-field ligand, so it increases the splitting energy, which gives rise to N. NH low-spin complex. For this reason, oxyhemoglobin absorbs at the blue (high-energy) end of the spectrum, which accounts for the bright red color of arterial blood. The position of the Fe2* ion relative to the plane of porphin ring also depends on this sixth ligand. Bond to O,, Fe is in the porphin plane; bound to H,0, it moves out of the plane slightly. This tiny (-60 pm = 6 x 10¬11 m) change in the position of Fe* on release or attachment of 0, influences the shape of its globin chain, which in turn alters the shape of a neighboring globin chain, triggering the release or attachment of its 02, and so on to the other two globin chains. The very survival of vertebrate life is the result of this cooperate "teamwork" by the four globin chains because it allows Heng maue hemoglobin to pick up O2 rapidly from the lungs and unload it rapidly in the tissues. Carbon monoxide CO is highly toxic because it binds to Fe2* ion in heme about 200 times more tightly than 02, thereby eliminating the heme group from functioning in the circulation. Like O2, CO is a strong-field ligand and produces a bright red, "healthy" look in the individual. Because heme binding is an equilibrium process, CO poisoning can be reversed by breathing extremely high concentration of O2, which effectively displaces CO from the heme: Heme-CO + 0,S Heme- 02 + CO Porphin ring which is a very effective chelating agent, is among the most common biological ligands. Chlorophyll, the photosynthetic pigment of green plants, is a porphyrin with Mg2* at the center of the porphin ring, and vitamin B12 has Co* at the center of a very similar ring system. OH you-
Transcribed Image Text:Complex ions in Living systems Despite the structural complexity of biomolecules, the principles of bonding and d-orbital splitting are the same as in simple inorganic systems. In this discussion we focus on iron. Iron plays a crucial role in oxygen transport in all vertebrates. The oxygen-transporting protein hemoglobin consists of four folded protein chains called globins, each cradling the iron-containing complex heme. Heme is a porphyrin, a complex derived from a metal ion and tetradentate ring ligand known as porphin. Iron (II) is centered in the plane of the porphin ring, forming coordinate covalent bonds with four N lone pairs, resulting in a square planar complex. When heme is bound in hemoglobin, the complex is octahedral, with the fifth ligand of iron (II) being an N atom from a nearby amino acid (histidine), and the sixth an O atom from either an O, (shown) or an H,0 molecule. Hemoglobin exists in two forms, depending on the nature of the sixth ligand. In the blood vessels of the lungs, where O2 concentration is high, heme binds 0, to form oxyhemoglobin, which is transported in the arteries to 0,-depleted tissues. At these tissues, the O, is released and replaced by H,0 molecule to form deoxyhemoglobin, which is transported in the veins back to the lungs. The H,O is a weak-field ligand, so the d ion Fe2* in deoxyhemoglobin is part of a high-spin complex. Because of the relatively small d-orbital splitting, deoxyhemoglobin absorbs light at the red (low-energy) end of the spectrum and looks purplish blue, which accounts for the dark color of venous blood. On the other hand, O2 is a strong-field ligand, so it increases the splitting energy, which gives rise to N. NH low-spin complex. For this reason, oxyhemoglobin absorbs at the blue (high-energy) end of the spectrum, which accounts for the bright red color of arterial blood. The position of the Fe2* ion relative to the plane of porphin ring also depends on this sixth ligand. Bond to O,, Fe is in the porphin plane; bound to H,0, it moves out of the plane slightly. This tiny (-60 pm = 6 x 10¬11 m) change in the position of Fe* on release or attachment of 0, influences the shape of its globin chain, which in turn alters the shape of a neighboring globin chain, triggering the release or attachment of its 02, and so on to the other two globin chains. The very survival of vertebrate life is the result of this cooperate "teamwork" by the four globin chains because it allows Heng maue hemoglobin to pick up O2 rapidly from the lungs and unload it rapidly in the tissues. Carbon monoxide CO is highly toxic because it binds to Fe2* ion in heme about 200 times more tightly than 02, thereby eliminating the heme group from functioning in the circulation. Like O2, CO is a strong-field ligand and produces a bright red, "healthy" look in the individual. Because heme binding is an equilibrium process, CO poisoning can be reversed by breathing extremely high concentration of O2, which effectively displaces CO from the heme: Heme-CO + 0,S Heme- 02 + CO Porphin ring which is a very effective chelating agent, is among the most common biological ligands. Chlorophyll, the photosynthetic pigment of green plants, is a porphyrin with Mg2* at the center of the porphin ring, and vitamin B12 has Co* at the center of a very similar ring system. OH you-
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