Triacylglycerols
Also known as triglycerides or neutral fats1.
Structure
Triacylglycerols are composed of 3 fatty acids, each in ester linkage. An ester linkage is a chemical bond between an acid and an alcohol. In triacylglycerols, the ester linkage consists of an acid (fatty acid) and it is chemically bound to an alcohol (glycerol)1.
Function
Triacylglycerols are nonpolar and hydrophobic molecules since the polar hydroxyls of glycerol and the polar carboxylates of the fatty acids are bound in ester linkages1. Due to their nonpolar and hydrophobic state, triacylglycerols are essentially insoluble in water, which is crucial for their role in energy storage.
Simple & Complex
Triaglyceroles consisting of a single type of fatty acid in all 3 positions is called “simple triacylglycerols” and are named after the fatty acid.
Most naturally occurring triacylglycerols are mixed1
To name non-simple triacylglycerols without ambiguity, the name and position of each fatty acid must be specified1.
Role in Energy Storage
In vertebrates, triacylglycerols are stored in specialized cells called “adipocytes”, or “fat cells”1. These adipocytes store large amounts of triacylglycerols as fat droplets that nearly fill the cell1.
Versus polysaccharides
Triacylglycerols have 2 significant advantages that make it better for energy storage than polysaccharides (starch or glycogen)1.
- Fatty acid carbon atoms are more reduced and therefore yield more (>2x) energy
- Triacylglycerols are hydrophobic and do not need to be hydrated1. Oppositely, polysaccharides need to be hydrated and thus require the organism to carry extra water to maintain polysaccharide hydration1.
Triacylglycerols can hold much more energy (weeks to months) than glycogen1. Glycogen has its benefits since it can produce metabolic energy quicker due to their water solubility1.
Serum
Blood test for serum triglycerides