Fat, a Primer

Humans store fat in specialized cells called adipose cells (or simply, fat cells). Adipose cells are almost entirely made out of triacylglycerols. They specialize in the synthesis, storage and mobilization of triacylglycerides. Triacylglycerols are also known as triglycerides or fats. They are made out of three fatty acid chains attached to a glycerol backbone. Large lipid-protein particles called lipoproteins ferry triacylglycerol around the body. Simple triacylglycerols have three identical fatty acids attached to their glycerol backbone. Mixed triacylglycerols have two or three different fatty acids.

Fatty acids are made of a hydrocarbon chain (a chain of hydrogen and carbon) and a terminal carboxyl acid group. The chains found in biology are usually unbranched and have an even number of carbon atoms, commonly having 16 or 18 carbon atoms. A fatty acid is saturated when all carbon atoms in its chain have a hydrogen atom. Fatty acids are unsaturated when there is at least one double bond in its structure. There are two types of unsaturated fatty acids: monounsaturated and polyunsaturated. Monounsaturated means there is one double bond in the structure of the fatty acid. It is polyunsaturated when there are two or more double bonds in the structure. The double bonds of polyunsaturated fatty acids are separated by at least one methylene group. The length of the chain and the number of double bonds determines the properties of the fatty acid. Fatty acids have four major biological roles:

  1. They act as fuel molecules, as in triacylglycerols as described above.
  2. They make up essential parts of biological membranes.
  3. They modify numerous proteins.
  4. Fatty acid derivatives act as hormones and intracellular second messengers.

The importance of fat for an organism is not to be underestimated. When it is ingested, it needs to be processed (metabolized). For fat metabolism, remember its structure, the backbone containing three strands.

Further Reading

Lipid. Encyclopedia Britannica. https://www.britannica.com/science/lipid

Triglyceride. Encyclopedia Britannica. https://www.britannica.com/science/triglyceride