Proteins: Proteins are the primary building materials of the body. Your hair, skin, muscles, and organs are composed mostly of proteins. Proteins are strong yet flexible, and they have a complex 3-D structure. Amino acids are the basic building blocks of proteins. Amino acids have an NH2 (amine) group on one end, a H-O-C=O (carboxyl) group on the other end, making it acidic, and an R group which extends from the central carbon atom. The R group could be just a hydrogen or a more complex molecule. There are 20 amino acids that are important to humans, and all proteins are made from combinations of these subunits. Chains of amino acids are called peptides.

Fats (lipids): Fats are the primary storage molecules of the body. Fats are very compact and light weight, so they are an efficient way to store excess energy. A fat is made up of a glycerol, which is attached to 3 fatty acid chains. Saturated fatty acids have no double bonds and hold the maximum number of hydrogens. Unsaturated fatty acids have some double bonds and therefore hold fewer hydrogens. Saturated fats are not as good for you as unsaturated fats.

Carbohydrates: Glucose, a sugar, is a simple carbohydrate. Sugar is a source of quick energy for the body because it is easily metabolized. Complex carbohydrates are made by stringing together long chains of glucose subunits. Animals convert excess sugar into glycogen for storage. Glycogen is a complex storage molecule made from glucose using insulin. Diabetics, who lack insulin, cannot make glycogen so they excrete excess sugar in their urine. Plants convert glucose into complex carbohydrates such as starch.

Nucleic Acids: These molecules contain the genetic code, which has all the information necessary to build the body. The basic unit is called a nucleotide, which is composed of a sugar-phosphate backbone attached to a nitrogenous base. Note that the DNA molecule shown below is double stranded, and that the two strands run in opposite directions.