A. Importance of carbon
1. Introduction
a. Although cells are 70-95% water, the rest consists mostly of carbon-based compounds.
b. Proteins, DNA, carbohydrates, and other molecules that distinguish living matter from inorganic material are all composed of carbon atoms bonded to each other and to atoms of other elements.
c. These other elements commonly include hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), and phosphorus (P).
2. Carbon atoms are the most versatile building blocks of molecules.
a. With a total of 6 electrons, a carbon atom has 2 in the first shell and 4 in the second shell.
b. Carbon completes its valence shell by sharing electrons with other atoms in four covalent bonds.
c. This makes large, complex molecules possible. (Fig. 4.2)
3. Variation in carbon skeletons contributes to the diversity of organic molecules.
a. Carbon chains vary in length and may be straight, branched, or arranged in closed rings.
b. The carbon skeletons may also include double bonds. (Fig. 4.4)
B. Functional groups
1. Functional groups contribute to the molecular diversity of life.
a. General (Table 4.1)
1. Functional groups are attachments that replace one or more hydrogen atoms to the carbon skeleton.
2. Each functional group behaves consistently from one organic molecule to another.
3. The number and arrangement of functional groups helps give each molecule its unique properties.
b. In a hydroxyl group (-OH), a hydrogen atom forms a polar covalent bond with an oxygen which forms a polar covalent bond to the carbon skeleton.
1. Because of these polar covalent bonds hydroxyl groups improve the solubility of organic molecules.
c. A carboxyl group (-COOH) consists of a carbon atom with a double bond with an oxygen atom and a single bond to a hydroxyl group.
d. An amino group (-NH2) consists of a nitrogen atom attached to two hydrogen atoms and the carbon skeleton.
1. Amino acids, the building blocks of proteins, have amino and carboxyl groups.
e. A phosphate group (-PO4) consists of phosphorus bound to four oxygen atoms (three with single bonds and one with a double bond).
1. A phosphate group connects to the carbon backbone via one of its oxygen atoms.
2. One function of phosphate groups is to transfer energy between organic molecules.