BioChemistry - CARBON AND THE MOLECULAR DIVERSITY OF LIFE...

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CARBON AND THE MOLECULAR DIVERSITY OF LIFE Organic chemistry is the study of carbon-based compounds. Carbon is a primary constituent of living things along with hydrogen, nitrogen, oxygen, sulfur, and phosphorous. Carbon, because it has a valence of 4 (it forms four bonds) imparts tremendous diversity to organic compounds. Organic compounds are primarily composed of C, H, N, O, S, and P in a virtually infinite number of arrangements. Of course, rules of bonding based on the valence shell electrons must be followed. Nitrogen and phosphorous have a valence of 3, oxygen and sulfur have a valence of 2, and hydrogen 1. Carbon forms four bonds at angles of 109 o to form a tetrahedron. Although convenient to write structural formulas with right angles, the actual shape is a tetrahedron. Organic molecules and their respective shapes will be explored in lab. Your book introduces you to organic molecules with various diagrams and pictures. Review also the valence of important atoms. HYDROCARBONS Hydrocarbons are a special set of organic molecules composed of only H and C atoms. There is a tremendous diversity of these molecules alone. A principal feature of all organic molecules, including hydrocarbons, is the carbon skeleton. Variation in the number of carbons in the skeleton produces short and long chain molecules. The chains may be branched or unbranched ; unique branching creates isomers. The presence of and number of double covalent bonds is also a basic variation in hydrocarbon molecules. The location of double bonds may also create isomers. Hydrocarbons may be saturated or unsaturated based on amount of double bonds. Saturated and unsaturated is used to describe organic molecules such as fats as well as simple hydrocarbons. · Saturated hydrocarbons have no double bonds (H exists at every possible location around all the carbons). · Unsaturated hydrocarbons have double bonds (at least one) and therefore contain less H than they could if saturated. · Each double bond removes two H from the hydrocarbon. Molecules may be ring ( cyclic ) shaped as well. Ring structures may have double bonds within them. In biology, ring molecules of 5 or 6 atoms (carbon mostly but
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the ring may include N, O, or S) are fairly common. To form a ring an H must be removed from each end of the ‘linear’ hydrocarbon and a bond formed to loop the ends to each other. Molecules may shift between linear and cyclic structures naturally; some sugars like glucose due this under certain conditions. SO WHAT ARE ISOMERS? Isomers are organic molecules with identical molecular formulas (number and type of atoms) and different structural formulas (arrangement of atoms). In this regard, isomers impose another source of diversity to organic molecules. As long as the molecular formula is the same and bonding is legitimate, the entire set of isomers for a molecule is all possible different arrangements of the atoms. If one changes the molecular formula, the molecule changes and one does not have an isomer. This is akin to protons in atoms and as long as one doesn’t change the
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