Week 2 - Reading (Part 1)

Week 2 - Reading (Part 1) - Primer on Biological Molecules...

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Primer on Biological Molecules Organic Compounds All living things are composed of organic compounds. Generally, organic compounds are distinguished from inorganic compounds by the presence of both carbon and hydrogen. We are referred to as carbon-based life forms, as is all life on earth. This means that carbon is a component of most of the chemical molecules that make up living organisms on this planet. Why is carbon so ubiquitous in nature? Carbon's participation in organic chemistry is probably due to its relatively unique chemical bonding properties. These properties allow carbon to participate in the formation of an incredibly wide variety of chemical compounds and electron configurations. Carbon is also a relatively small, non-bulky atom so it can share electrons easily with other atoms. Carbon, atomic number six, has six electrons. Two are in the first electron shell and four are in the second electron shell. Carbon must share four electrons with other atoms to fill its outermost electron shell and attain a stable configuration. Carbon atoms can share electrons with a wide variety of elements also commonly found in organic compounds, the most notable being other carbon atoms, hydrogen atoms and oxygen atoms. As a matter of fact, the simplest organic molecules are defined as being comprised of only carbon and hydrogen, and are therefore referred to as hydrocarbons. Hydrocarbons are non-polar, hydrophobic compounds. The term hydrophobic comes from the Latin roots "hydro" (water) and "phobia" (fear). Literally speaking, a hydrophobic compound is afraid of water. The term non-polar is often used in conjunction with the term hydrophobic, because those compounds that have no charges on them will not mix with polar water. A non-polar compound repels a polar solvent and collects together in a film on top of the solvent, or forms a layer on the bottom of the container. Most oils, waxes, and fat compounds are hydrocarbons, as are the fossil fuels gasoline, kerosene, and similar compounds. Just think of how well these compounds mix with water and you'll easily grasp the concept of hydrophobicity. Since we have introduced the concept of hydrophobicity we should discuss its complement, hydrophilicity. Hydrophilic comes from the Latin roots "hydro" (water) and "philia" (love). Hydrophilic compounds love water, and mix with it easily. These compounds are polar, and so dissolve easily in the polar solvent water. Figure 1. Structural formulas of some simple hydrocarbons. Methane CH 4 Ethane C 2 H 6 Propane C 3 H 8 Ethylene C 2 H 4
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Now that you have seen the structures associated with the bonds around carbon, let's discuss how carbon can form so many different compounds. Carbon always needs to share four electrons to fill its outermost electron shell. Each straight line extending from the carbon in the diagrams represents one electron carbon is sharing with another atom. In turn, that atom shares one of its electrons with carbon, forming a covalent bond. Each
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This note was uploaded on 04/02/2008 for the course ENGR 213 taught by Professor Clague during the Spring '08 term at Cal Poly.

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Week 2 - Reading (Part 1) - Primer on Biological Molecules...

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