Like the carbohydrates, proteins are composed of smaller units. The monomers that make up proteins are calledamino acids. There are around twenty different amino acids. The structure of the amino acid glutamine is depicted below.


The term lipid refers to a wide variety of biomolecules including fats, oils, waxes and steroid hormones. Regardless of their structure, location or function in a cell/body, all lipids share common features that enable them to be grouped together.

  • They do not dissolve in water; they are hydrophobic.
  • Like the carbohydrates, they are composed primarily of carbon, hydrogen and oxygen.

The hydrophobic nature of the lipids dictates many of their uses in biological systems. Fats are a good source of stored energy while oils and waxes are used to form protective layers on our skin, preventing infection. Some lipids, the steroid hormones, are important regulators of cell activity. We will revisit this during our discussion of the information flow in cells. The activities of steroid hormones such as estrogen have been implicated in cancers of the female reproductive system. Treatments based on this knowledge will be discussed in detail in the treatment section of the site.

Depicted above is an example of a triacylglycerol, or fat. The three long chains are composed only of carbon and hydrogen and this gives the molecule its hydrophobic properties. When you read about saturated and unsaturated fat content on a food label, they are referring to differences in these long hydrocarbon chains.