Section 3.0: Lipids — Long-Term Energy, Membranes, and Messengers

Lipid

A diverse group of hydrophobic organic molecules, including fats, oils, phospholipids, and steroids, grouped together because they are nonpolar and do not dissolve in water.

Hydrophobic

Pertaining to nonpolar, "water-fearing" molecules (or parts of molecules) that do not dissolve in water.

Fat (Triglyceride)

A large lipid made from one glycerol molecule linked to three fatty acid molecules. This is the body's primary form of long-term energy storage.

Saturated Fatty Acid

A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds. These chains are straight, pack tightly, and are typically solid at room temperature.

Unsaturated Fatty Acid

A fatty acid that has one or more double bonds between carbons in its hydrocarbon tail, which creates kinks or bends in the chain. These bends prevent tight packing, making them liquid at room temperature (e.g., oils).

Phospholipid

A lipid made up of a glycerol joined to two fatty acids and a phosphate group. They are the main component of all cell membranes.

Hydrophilic

Pertaining to polar or charged molecules (or parts of molecules), such as the phosphate head of a phospholipid, that are "water-loving" and soluble in water.

Amphipathic (Phospholipid property)

The dual nature of a phospholipid, meaning it has both a hydrophilic (water-loving) phosphate head and hydrophobic (water-fearing) fatty acid tails. This is critical for forming the cell membrane barrier.

Steroid

A type of lipid in which the carbon skeleton is bent into four fused rings.

Cholesterol

The most common steroid, which is an important component of animal cell membranes and serves as the starting material for making other steroids, including sex hormones.