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VTU eNotes On Structural Biology (Bio-Technology)

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Publisher VTU eLearning
Author: Panel Of Experts
Number of Pages 287
Available Available in all digital devices
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biomolecules. One of these, water, may constitute 50-95 of a cell s content by weight, while ions such as sodium, potassium and calcium may account for another 1 . Almost all other kinds of molecules are organic which are principally composed of six elements C,H2,O2,N2,P and S. The properties of one element carbon are responsible for the almost infinite variety of organic molecules. Carbon atoms can form 4 strong covalent bonds either to other carbon atoms or to atoms of other elements. Of central importance in organic chemistry are the hydrogen and carbon containing compounds called hydrocarbons. Although hydrocarbons are relatively unimportant in living organisms, but several aspects of their chemistry are relevant to the biochemistry. The number of compounds that contain carbon are many times greater than the number of compounds that do not contain carbon. Organic molecules containing thousands of atoms the arrangement of atoms in molecules can be very complicated hence to determine the structure of compounds. The answer to this question came to August Kekule. Carbon atoms can form long chains of thousands of atoms or rings of all sizes the chains and rings have branches and crosslinks. Each different arrangement of atom corresponds to a different compound and each compound has its own characteristic set of chemical and physical properties. It is not surprising that more than 10 million compounds of carbon are known today and that this number is growing by half a million per year. In 1990, the journal science selected diamond, one of the allotropic forms of carbon as the molecule of the year and a runner-up was another newly developed allotrope of carbon, C60 Buckminsterfullerene. In 1916, two kinds of chemical bonds were described the ionic bond by Walther Kossel in Germany and the covalent bond by G.N.Lewis University of California . The introduction of quantum mechanics in 1926 by Erwin Schrodinger of university of Zurich caused a tremendous change in ideas about how molecules are formed. Atom has a positively charged nucleus surrounded by electrons arranged in concentric shells or energy levels called orbit. There is a maximum number of electrons that can be accommodated in each shell 2 in 1st shell, 8 in 2nd shell, 8 or 18 in 3rd shell and so on using. The greatest stability is reached when the outer shell is full, as in noble gases. Both ionic and covalent bonds arise from the tendency of atoms to attain a stable configuration of electrons. Structure of Water Water H2O is composed of 2 atoms of hydrogen and 1 atom of oxygen. Each hydrogen atom is linked to 2 oxygen atom by single covalent bond . Since oxygen is more electronegative than hydrogen , there is a separation of charge within the molecule .i.e. asymmetrical and have a band geometry with a bond angle of 104.5 due to unbalanced distribution of charge, becomes
dipolar. Since water has got opposite charges on two points and due to large difference in electronegativity of hydrogen and oxygen the hydrogen of water molecules are attracted to unshared pairs of electrons of another molecule. This non-covalent relationship is called hydrogen bond, which is due to strong electrostatic action rather than a true bond. In addition to hydrogen bonds, the water interact with other molecules through three more types of non-covalent interactions. The electrostatic interaction causes hydration of ions and solvation of charged species in water. Van der waals forces are weak transient electrostatic interactions between permanent or induced dipoles. Hydrophobic interactions when water mixed with non-polar substances, they coalesce into droplets because water-water interactions are stronger than non-polar interactions. Water has a variety of unusual properties because of attractions between two polar regions. The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. Each water molecule can form hydrogen bonds