Wednesday, November 7, 2007

The Chemistry of Life

Chemistry is the foundation of biology. About twenty-five chemicals are necessary for life, and only four create about 96 % of living matter. Those four elements are carbon, oxygen, hydrogen, and nitrogen. We cant live without COHN.

Bonding properties of atoms depend on the number of electrons in the valence shell. Oxygen is the most electronegative element on the periodic table, it is the most reactive. Covalent bonds are strong bonds because the electrons are shared between the atoms. They are very stable. There are polar and nonpolar covalent bonds. In polar covalent bonds, electrons are shared unequally, such as in water.

Hydrogen bonds, ionic bonds, hydrophobic and hydrophilic interactions, and van der Waals forces are examples of weak bonds. Hydrogen bonding can happen anywhere an -OH exists in a larger molecule. It occurs when polar water creates molecular interactions.

All life occurs in water, whether under the sea or inside the cell. Without water life could not exist. Water is very unique. It is cohesive, water molecules are attracted to each other, and adhesive, water molecules stick to other things. These are the reasons that water can reach the top of trees. Its a good solvent, most things can dissolve in water. Hydrophilic substances, which are polar, dissolve in water and hydrophobic substances, which are nonpolar, do not. It has lower density as a solid, which is very rare, actually nothing else has that property. The fact that water does this is not only an amazing phenomenon, but it enables life on Earth to continue. If ice sank, all bodies of water would completely freeze over time and there would not be enough time in the summer for it to thaw, therefore life could not exist. It has a very high specific heat, its very resistant to temperature change, and it takes a lot of energy to heat and cool water. Water moderates temperatures on Earth. And finally it has a high heat of vaporization. When water evaporates off of your skin it cools you off, which is why we sweat and why animals pant when they’re hot.

Water ionizes, H+ splits off leaving -OH, if they’re equal then the solution is neutral. If H+ is greater, the solution in acidic and if -OH is greater, the solution is basic. The pH scale shows how acidic or basic a solution is, 0 is most acidic, 7 is neutral, and 14 is the most basic. There are buffers to help regulate pH levels. The pH of a molecule affects its shape which affects its function. These buffers donate or absorb H+ when it falls or rises to maintain a level of about 7.

Tomorrows sherpa will be Kerrie.

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