Triglycerides and phospholipids are two major classes of lipids, and lipids are one of the major classes of biological molecules. Although these two types of lipids are similar (almost identical to the untrained eye), they are vastly different in both feature and function.
Similarities
Triglycerides and phospholipids are both lipid derivatives of glycerol, which is a three-carbon molecule with three attached hydroxyl groups. The oxygen atoms of the three hydroxyl groups are readily reactive, and cells utilize this reactivity to synthesize both classes of lipids. Triglycerides and phospholipids both contain long-chain fatty acids attached to one or more of the glycerol molecule's hydroxyl groups. Both classes of lipids can utilize the same types of fatty acid chains, in terms of both length and saturation.
Triglyceride Features
Triglycerides, also known as triacylglycerols, contain three fatty acid chains attached to the three available hydroxyl groups on glycerol. The three fatty acid chains can all be the same, as in the case of simple triglycerides. The triglyceride could also contain multiple types of fatty acid chains; these are known as mixed triglycerides. Triglycerides are heavily nonpolar and tend to form aggregates in polar solvents such as water, whereas they will readily dissolve in nonpolar solvents like carbon tetrachloride.
Phospholipid Features
In contrast to triglycerides, phospholipids are amphipathic, which means that they are both polar and nonpolar. Phospholipids only have two fatty acid chains, and these chains confer hydrophobicity to the molecule. However, the third hydroxyl group on the glycerol chain is linked to a phosphoryl group, which can then be further modified by prosthetics such as serine, ethanolamine, inositol, or a second glycerol molecule. These secondary modifications confer hydrophilicity to the molecule. Depending on the number available, phospholipids tend to aggregate into micelles or bilayers.
Triglyceride Functions
The primary function of triglycerides is long-term energy storage; these molecules are extremely efficient for storage purposes, because there is a great amount of energy in the carbon-carbon bonds in the fatty acid chains. The sugar stores in our body would only allow us to survive for a short time, but the fat content of a normal human being would allow for weeks of starvation. The human body possesses the ability to quickly switch between triglyceride synthesis and triglyceride metabolism.
Phospholipid Functions
Phospholipids are the main component of the plasma membrane found around every single living cell on earth. Due to their amphipathic nature, phospholipids in a membrane have their hydrophobic fatty acid chains facing into the membrane and their polar phosphoryl head groups facing out into the aqueous environment. Membranes are protective physical barriers for cells, and the amphipathic nature of phospholipids is the reason why they make good barriers.
Tags: acid chains, fatty acid, fatty acid chains, hydroxyl groups, classes lipids, Triglycerides phospholipids