ABSTRACT
Proteins are biology’s workhorse molecules. In a human cell, there are about 18,000 different types of protein molecules. Think of cells as teeming factories of molecules of various types. Proteins perform many functions-as the factory workers, as the machines that produce the factory’s output, and as the factory’s structural framework. In contrast, nucleic acids (DNA and RNA) are the molecules that encode information, providing the instructions for making the factory products. Sugars and carbohydrates are energy sources used to run the factory. The factory walls (cell membranes) are made up primarily of lipids and polysaccharides. E. coli is a bacterium having about 4300 protein-coding genes and a total of about 3 × 106 individual protein molecules [1]. Figure 1.1 shows the size of a typical protein molecule compared with atoms and cells.
