Bio-inorganic chemistry introduction and applications

Bioinorganic Chemistry for intermediate level

1. Unit : 11- Bio-inorganic Chemistry Out Line of Lecture: 1.Introduction 2.Micro and macro nutrients. 3.Essential trace elements 4.Biological role of few ions in biological system 5.Metal toxicity due to iron , arsenic, mercury, lead and cadmium . Lecture By Ram Darash Pandey (Assistant Professor) Department of Chemistry Amrit Campus, Thamel , Kathmandu Tribhuvan University

2. “Bioinorganic Chemistry “is at the gate-way of inorganic chemistry and biochemistry, i.e. it describes the mutual relationship between these two sub-disciplines, with focus upon the function of inorganic “substances “in living systems, including the transport, speciation and, eventually, mineralization of inorganic materials, and including the use of inorganics in medicinal therapy and diagnosis. These “substances” can be metal ions (such as K+, ferrous and ferric), composite ions (e.g. molybdate), coordination compounds1 (like cisplatin and carbonyl technetium), or inorganic molecules such as CO, NO, O3. Medicinal inorganic chemistry on the one hand, and biomineralization on the other hand, are important integral parts. Fig: Periodic Table of the bio-elements: elements building up bio-mass , additional essential elements , essential for some groups of organisms , medicinally important elements

3. Micro and Macro nutrients (Essential and Trace elements) Out of 118 known elements, there are about 40 elements involved in the life process of living organisms. Out of which about 30 elements are essential for healthy human beings. The elements that are required in large amounts are called macronutrients or principal elements and the elements which are required in small quantities are called micronutrients. Essential elements The elements which are required for the maintenance of life are called essential elements. Absence of these elements results in death or a severe malfunction of the organs in the organism. These cannot be wholly replaced by any other element. Trace elements They play an important role in the biological system. Deficiency of these elements cause the serious defect in the living organisms. Many biological reactions are catalyzed by the enzyme which is catalyzed by the metals. Out of thirty essential elements required for biological process, 19 are trace elements. Trace elements are also differentiated into trace elements and ultra-trace elements. The specific role of each of these is discussed below:   Classification of the essential elements 1. Bulk structural elements : H, C, N, O, P, S Macro minerals : Na, K, Mg, ca, Cl Trace elements : Fe, Zn, cu 4. Ultra-trace elements : Nonmetals : F, l, se, Si, As, B Metals : Mn, Mo, Co, Cr, V, Ni, Cd, Sn, Pb, Li

4. Na + – K + Pump (Also Called Sodium Pump) Although Na + and K + ions are chemically similar, yet biological response for these ions is different. While Na + ions are pumped out of cyto-plasm, K + ions are pumped in. This transport of ions is called Na + – K + pump or simply sodium pump. This pump involves the active take up of K + ions and expulsion of Na + ions. The difference in concentration of the two ions inside and outside the cell membrane produces an electrical potential, which is crucial for the functioning of nerve and muscle cells. It may be noted that higher intake (we require about 1 g of Na + per day) of Na + ions is a problem, but there is no such risk from higher intake of K + ions. Rather potassium deficiency is more common. We can make up the K + ions deficiency by consuming more of banana and coffee. Na + and K + are present in the red blood cells. The ratio of these ions in mammals such as human being, rabbits, rats and horses is l:7. In cats and dogs, this ratio is 15: l. To establish this ratio also called concentration gradient in the cell, biologists have suggested different mechanism involving sodium pump and potassium pump. Mechanism of Na + – K + Pump The mechanisms of Na + – K + pump is that Na + ATPase is phosphorylated by adenosine tri-phosphate molecule (ATP) in presence of Na + and Mg 2+ . The site for phosphorylation is the side chain of a specific asparate residue, E. In this reaction phosphorylated inter-mediate (E-P) is formed.

5. Phosphorylation of E Dephosphorylation of E: E – P formed is hydrolyzed in presence of K + ions. As a result, E – P gets dephosphorylated to form the original E. It has been found that Na + and Mg 2+ ions are necessary for the formation of the intermediate (E–P) and K + ions are necessary for dephosphorylation of the intermediate. During this reaction 3Na + and 2K + ions are transported per ATP hydrolyzed. Therefore, the pump generates an electric current across the plasma. In other words, Na + – K + ATPase pump is electrogenic. Each operation of the cell pumps out larger number of Na + ions that it pumps into the cell. As a result, the interior of the cell acquires an excessive negative charge while the exterior of the cell acquires an excessive positive charge. As a result, electrical potential gradient across the cell membrane is developed which is responsible for the transmission of nerve signals in the animals. ATP is not hydrolyzed unless Na + and K + are transported. In other words, the system is coupled. The energy stored in ATP is only dissipated if the pump works. The Na + – K + pump is also reversible so that it synthesizes ATP https://www.khanacademy.org/science/high-school-biology/hs-energy-and-transport/hs-passive-and-active-transport/v/sodium-potassium-pump-video

6. Sodium Glucose pump