Lipids are one of the 4 biological macromolecules defined as being non-polar with an inability to be easily dissolved in water, they are mainly used for cell signaling, the storage of energy, and as structural components of cell membranes. Although lipids are organized into a wide range of subcategories, many of these subcategories contain only a slight change in characteristics from the 3 main categories of lipids; triglycerides, phospholipids, and steroids. Triglycerides are composed of a glycerol molecule with three fatty acid molecules attached to it, their biological purpose is to store energy efficiently. A Triglyceride will be saturated if there is only a single bond between the carbons in the hydrocarbon chain and unsaturated if a double bond is present. Saturated triglycerides tend to be solids at room temperature and are obtained primary through dairy products such as creams, cheeses, butters, and fatty meats. Unsaturated triglycerides tend to be liquids at room temperature and are generally found in plant foods such as nuts and seeds. Triglycerides consumed are stored in specialized fat cells called adipocytes forming adipose tissue throughout the body; this tissue is how the body efficiently stores energy for later use. Another main category of lipids are phospholipids, they are composed of two fatty acid molecule tails attached to a head composed of a glycerol molecule attached to a phosphate group. Phospholipids are amphipathic with a hydrophilic head and a hydrophobic tail, this is vital in its function. Phospholipids placed in water naturally arrange themselves into a sphere-shaped bilayer called a micelle with their hydrophilic heads facing the water and their hydrophobic tails facing inward. This characteristic allows phospholipids to perform its main biological function of forming the plasma phospholipid bilayer membrane incasing cells. Phospholipids allow the cell membrane to be semi permeable and extremely fluid. The final category of lipids are steroids, they are composed of four linked carbon rings with a possible tail and –OH group. Although steroids don’t resemble other lipid structures, they are considered lipids due to the fact that they are hydrophobic. Steroids are chemical messengers such as Testosterone, Estrogen, Adrenalin, and cortisol, which are transported through the blood stream to regulate essential body processes. Lipids unique characteristics allow it to play vital roles in biology and without lipids life on earth as biologists understand it today would not be possible.

References:

https://www.khanacademy.org/science/biology/macromolecules/lipids/a/lipids