By Jennifer Stearns, Michael Surette

The cell needs many compounds for life, including enzymes to perform its many functions, structural molecules to give it shape, as well as nucleic acids to store its genetic material. If it can, the cell will obtain some of these things from its environment, but when it has to make them itself, it uses anabolism.

Anabolism is essentially making the complex things needed from smaller building blocks. These complex compounds are called macromolecules, and there are four main classes of them:

  • Proteins are made from amino acids.

  • Nucleic acids are made from nucleotides.

  • Polysaccharides, which are the subunits of complex carbohydrates like starch and glycogen, are made from sugars.

  • Lipids are made from fatty acids.

Many of these macromolecules combine not only with members of their own class, but also with those from other classes to form things like glycoproteins or lipoproteins that have important roles in microbial cell function and structure.

The building blocks themselves can sometimes be taken directly from the environment, but other times they have to be made. In many cases, complex pathways are needed to make the smallest subunits of each macromolecule, but, as you’ll see in this section, microbes have figured out ways to use the least number of complex pathways possible.