Carbon and the Molecular Diversity of Life Chapter 4 notes

Introduction Although cells are 70-95% water, the rest consists mostly of carbon-based compounds. Proteins, DNA, carbohydrates, and other molecules that distinguish living matter from inorganic materials are all composed of carbon atoms bonded to each other and to atoms of other elements. These other elements include hydrogen, oxygen, nitrogen, sulfur, and phosphorous.

What is organic chemistry? The study of carbon (organic) compounds These compounds can come from biological processes or they can be synthesized by non-living reactions. Organic compounds can range from simple molecules, such as CO2 or CH4, to complex molecules like proteins, that may weigh over 100,000 daltons.

Carbon atoms are versatile! With a total of 6 electrons, a carbon atom has 2 in the first shell and 4 in the second shell. Carbon usually does NOT form ionic bonds by losing or gaining 4 electrons. Carbon usually completes its valence shell by sharing electrons with other atoms in four covalent bonds. This tetravalence by carbon makes large, complex molecules possible.

What shape do carbon compounds have? When carbon forms covalent bonds with four other atoms, they are arranged at the corners of an imaginary tetrahedron with bond angles of 109o. While drawn flat, they are actually three-dimensional. When two carbon atoms are joined by a double bond, all bonds around the carbons are in the same plane. They have a flat, three-dimensional structure.

Carbon Models

Carbon Chains Carbon chains form the skeletons of most organic molecules. May vary in length and may be straight, branched, or arranged in closed rings May include double bonds

Hydrocarbons Hydrocarbons are organic molecules that consist of only carbon and hydrogen atoms. major component of petroleum Fats are biological molecules that have long hydrocarbon tails attached to a non-hydrocarbon component.

Isomers Isomers are compounds that have the same molecular formula but different structures and therefore different chemical properties. Sort of like twins 3 types…

1. Structural Isomers Structural isomers: molecules that have the same molecular formula but differ in the covalent arrangement of atoms. Ex: butane and isobutane have the same molecular formula C4H10, but butane has a straight skeleton and isobutane has a branched skeleton.

2. Geometric isomers Geometric isomers: compounds with the same covalent partnership that differ in their spatial arrangement around a carbon-carbon double bond. The double bond does not allow atoms to rotate freely around the bond axis. The biochemistry of vision involves a light-induced change in the structure of rhodopsin in the retina from one geometric isomer to another

3. Enantiomers Enantiomers: molecules that are mirror images of each other. possible if there are four different atoms or groups of atoms bonded to a carbon. Like left-handed and right-handed versions Usually one is biologically active, the other inactive.

Enantiomer examples Even the subtle structural differences in two enantiomers have important functional significance because of emergent properties from the specific arrangements of atoms. One enantiomer of the drug thalidomide reduced morning sickness, its desired effect, but the other isomer caused severe birth defects. The L-Dopa isomer is an effective treatment of Parkinson’s disease, but the D-Dopa isomer is inactive.

Model Carbon Molecules With a partner, make a model of each of the following: CH4 (tetrahedron) Structural Isomers: butane and isobutane (you only need to build the Carbon molecules) Geometric Isomers: you design your own Enantiomer Isomers: Use the CH4 from #1 and change one H to something else. Then make the enantiomer of that molecule.