Biological Oxygen Transport - Essay Example

Bioinorganic Chemistry. The inorganic elements found in living organisms are basic building blocks made up of atoms and molecules. The most common elements found in the cells of living organism are Copper, Carbon, Chlorine, Calcium, Iodine, Iron, Hydrogen, Magnesium, Oxygen, Phosphorous, Potassium, Sulphur, Sodium, Zinc and Nitrogen. The major part of the solid substances of a living organism is made up of organic material. However, these organic compounds are not sufficient for the human body. In order to live, a living organism has to perform many chemical reactions. These chemical reactions cannot take place on their own or even if they can, they are slow to reach completion. The chemical reactions thus require enzymes to speed up their reaction. Most of the enzymes require metallic entities to help them function to their full capacity. Metallic ions like Zinc and Magnesium provide biological enzymes with good acid capability. Thus, the enzymes that are used for acid base reactions use magnesium and zinc at their active centers. In addition, inorganic compounds like sodium and potassium are required by living organism to create a potential difference across cell membrane. Unequal distribution of sodium and potassium ions across cell membrane help initiate an action potential. Hemoglobin is an iron containing oxygen transport metalloprotein that is found in the red blood cells of vertebras (Anthea, Human Biology And Health). Its structure exhibits characteristics of both quaternary and tertiary structures of protein (Kessel, 122 Print). Most amino acids present in the hemoglobin are alpha helices and are joined together by non-helical structures. Hydrogen bonds present in the helical structure stabilize the helical units and give hemoglobin molecule its specific shape (Hemoglobin Tutorial, University of Massachusetts Amherst) The hemoglobin molecule has a protein part globin to which a small iron containing group heme. The heme consists of a charged iron ion that is contained in a heterocyclic ring. This heterocyclic ring is known as porphyrin and it consists of four pyrrole molecules linked together with iron bound in the center (Hemoglobin-School of Chemistry, Bristol University, ). The iron ion is the oxygen-binding site of hemoglobin. The iron ion coordinates with four molecules of nitrogen. The iron ion is strongly bound to the protein via imidazole ring of the F8 histidine residue below porphyrin ring. A sixth position bind oxygen reversibly by coordinate bond to complete the octahedral group of six ligands (Wiki Premed, Coordinated Chemistry). When oxygen is not bound to the iron ion, the place is filled by water molecule to form a distorted octahedral structure. In normal human adult hemoglobin, the binding of oxygen to hemoglobin is a cooperative process. When hemoglobin molecule is saturated with oxygen, the first oxygen molecules bound to the hemoglobin increase the binding ability of the hemoglobin for more oxygen molecules. This positive cooperative binding is because of the conformational changes of the hemoglobin complex; when one unit of hemoglobin molecule binds with oxygen, it induces conformational changes in other subunits of the protein complex and enables other subunits to gain increased affinity for oxygen. Major part of body’s iron is contained in the red blood cells. It is contained in the protein hemoglobin. There are large numbers of molecules in a living body that contain heme. They all function mainly by changing the oxidation states of iron between oxidation state II and III. Iron gives up and takes up electrons when it switched between different oxidation states. In hemoglobin when Iron is in Fe (II) state, it binds with oxygen and carries this oxygen with blood to an oxygen deficient region. At the oxygen deficient area, it gives up its oxygen. In terms of chemical reactions, the binding of iron to oxygen can be written as O2 + Fe (II) (hemoglobin) ↔ O2--Fe (III) (hemoglobin) This shows that the reaction is reversible and can go in either forward direction or backward direction. The iron atom moves back in porphyrin ring towards the center of the plane when the oxygen binds to iron atom in hemoglobin. At the same instance, the imidazole side chains interacting at other poles of iron of histidine residue of are also pulled towards the porphyrin ring. This causes the plane of the porphyrin ring to move towards the outside of tetramer and it induces a strain in the helix that contain histidine residue, as it moves towards iron atom. This strain in then transmitted to other three remaining monomers in the tetramer, to induce same conformational change in other iron containing heme sides so that binding of oxygen to iron atoms at those sites become easier. The superoxide ions are produced in biological systems by reduction of molecular oxygen. They are powerful oxidizing agents and thus are toxic in nature. However, phagocytes to kill microorganisms use them. The superoxide dismutase (SOD) enzyme efficiently destroys superoxide ions when not needed. The key action of these enzymes is oxidation or reduction of a metal ion that has variable oxidation states. In humans, the metal present in SOD is usually copper and it is coordinated tetrahedrally with histidine residues. The enzyme also contains zinc ions. Other similar enzymes may contain iron, nickel and manganese The reaction of the enzyme can be written as Oxidation: M(n+1)+ + O2− → Mn+ + O2 Reduction: Mn+ + O2− + 2H+ → M(n+1)+ + H2O2. Copper is relatively not a major metallic element that is required by the living organisms. Copper is used for normal metabolic processes along with other vitamins and fatty acids. However, the human body cannot synthesize copper, thus regular supplements need to be taken to maintain normal levels of copper in body. Copper combines with certain enzymes that act as catalysts to perform different body functions. Some are required for providing energy that is required by different chemical reactions. Others are involved in formation of melanin pigment in skin. Still others are required for forming cross-link and elastin that repair and maintain connective tissues. Copper containing enzymes are thought to participate in different oxygen processing pathways. Zinc is an essential element and is involved in human metabolism. More than a hundred or so biological enzymes require zinc for their catalytic activity. Zinc is important in all biochemical reactions and plays a major role in duplication of genetic material including DNA transcription and translation of RNA. It is an important element for cell division thus; it is crucial element for a developing fetus. It is vital in activating proper growth of bones and height. When dietary intake of Zinc is insufficient, clinical abnormalities and signs may develop. This element is also important for non-specific and specific immune functions. In respect to non-specific immunity, zinc affects the integrity of barrier of epithelium and proper function of monocytes, neutrophils and macrophages. With regard to specific type of immunity, decreased levels of lymphocytes and their functions occur in zinc deficiency. Most of the nitrogen fixation is performed by activity of a molecule molybdenum nitrogenase present in microorganisms. (Igrashi, pg351-384). Molybdenum nitrogenase is widely found in nature and is composed of two proteins; a hetrotetrameric NifDK-protein component (a2B2 dinitrogenase) and a homodimeric NifH-protein component (dinitrogenase reductase) (Bulen, LeComte, pg979-986)The enzyme nitrogenase contained in certain microorganism, contains molybdenum at their active sites. Iron sulphur clusters in the enzyme are involved in transporting electrons to reduce nitrogen that is to be fixed. A host that develops a symbiotic relation with the microorganism that fixes nitrogen provides energy to the process. The relation is symbiotic because host, which is usually a legume plant, provides the microorganism with energy through photosynthesis and gets nitrogen in return: reaction: N2 +16 MgATP +8e- → 2NH3 + 16 MgADP+16 Pi + H2 There are many therapeutic uses of inorganic elements. Zinc for instance exerts its therapeutic effects by reducing the duration of colds by acting as an inhibitor to replication of virus that causes cold and prevent its entry in the cell (Korant, Butterworth,pg 298-306). Copper is another element whose inorganic compounds have been used for therapeutic purposes. Copper aspirintae and copper tryptophante are inorganic copper compounds that are used excessively to treat ulcers and heal wounds. In the human body, brain contains the maximum amount of copper. Thus, it is seen that copper is essential for normal functioning of the brain. Prepared copper complexes are thus used as anti-epileptic drug. Nitric oxide is an important signaling molecule in body of vertebras especially mammals. It is an important biological messenger playing a key role in many biological functions. The endothelium lining of blood vessels in vertebra use nitric oxide to relax the smooth muscles in the blood vessels and cause vasodilatation. It is a highly reactive molecule and crosses cell membrane rapidly. This property makes nitric oxide an ideal paracrine and endocrine signaling molecule (Stryer, Lubert, pg 732). Nitric oxide contributes to blood vessel homeostasis by preventing aggregation of platelets, by preventing contraction of smooth muscles of blood vessels and by preventing sticking of leucocytes to endothelium wall. Patients with diabetes and arthrosclerosis often show impaired nitric oxide signaling (Dessy, Ferron, 207-216). References Ochiai, E., “General Principles of Biochemistry of the Elements” (Plenum Press, New York. Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. van Kessel et al. "2.4 Proteins - Natural Polyamides." Chemistry 12. Toronto: Nelson, 2003. 122. Print. Hemoglobin Tutorial." University of Massachusetts Amherst. 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