Chapter02FALL05 - Chapter 2 - Water Must understand water...

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Chapter 2 - Water Must understand water and its properties. Why? Macromolecular components (i.e. proteins) assume shapes in response to water. Most metabolic machinery operates in an aqueous environment. Properties of Water 1) polarity Covalent bonds (electron pair is shared) between oxygen and hydrogen atoms with a bond angle of 104.5 o . Oxygen atom is more electronegative that hydrogen atom --> electrons spend more time around oxygen atom than hydrogen atom --> result is a POLAR covalent bond. Creates a permanent dipole in the molecule. Can determine relative solubility of molecules “like dissolves like”. 2) hydrogen bonds Due to polar covalent bonds --> attraction of water molecules for each other. Creates hydrogen bonds = attraction of one slightly positive hydrogen atom of one water molecule and one slightly negative oxygen atom of another water molecule. The length of the bond is about twice that of a covalent bond. Each water molecule can form hydrogen bonds with four other water molecules. molecules. Weaker than covalent bonds (about 25x weaker). Hydrogen bonds give water a high melting point . Density of water decreases as it cools --> water expands as it freezes--> ice results from an open lattice of water molecules --> less dense, but more ordered.
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Hydrogen bonds contribute to water’s high specific heat (amount of heat needed to raise the temperature of 1 gm of a substance 1 o C) - due to the fact that hydrogen bonds must be broken to increase the kinetic energy (motion of molecules) and temperature of a substance --> temperature fluctuation is minimal. Water has a high heat of vaporization - large amount of heat is needed to evaporate water because hydrogen bonds must be broken to change water from liquid to gaseous state. 3) universal solvent Water can interact with and dissolve other polar compounds and those that ionize (electrolytes) because they are hydrophilic. Do so by aligning themselves around the electrolytes to form solvation spheres - shell of water molecules around each ion. Solubility of organic molecules in water depends on polarity and the ability to form
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This note was uploaded on 08/02/2009 for the course BIOCHEMIST 100 taught by Professor Crew during the Spring '05 term at North Alabama.

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Chapter02FALL05 - Chapter 2 - Water Must understand water...

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