There are four major classes of small biological molecules found in cells. These are carbohydrates, lipids, amino acids, nucleotides. The different classes of compounds can be identified by their characteristic structural features. Lipids Lipids or fats are characterized by their insolubility in water and solubility in organic solvents or detergents.
Lipids are the most efficient energy storage molecules in cells.
Most of the structure of lipids is very non-polar, formed almost exclusively of carbon and hydrogen atoms. The presence of long, hydrophobic fatty acid chains is a key feature to use in identifying many important lipids. Amino Acids Amino acids are the building blocks of proteins. As shown in the diagram, amino acids have a generalized structure, including an amino group, carboxyl group, and variable side chain designated as the R-group. There are 20 different amino acids used to make proteins.