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Three Different Types of Lipids

The word "lipid" derives from the Greek word "lípos," which refers to both animal fats and vegetable oils. In accordance with the meaning of the Greek word, the scientific term "lipid" designates such substances as beef and pork fat and olive oil. But there are two other principal types of lipids: components of cell membranes called phospholipids and such substances as cholesterol.

  1. Fats and Oils

    • The first type of lipids consists of fats and oils. Fats and oils are similar chemical substances. They both contain carbon and hydrogen atoms, with very few oxygen atoms hidden away in the center of the molecule. Both are insoluble in water. But there are two differences. First, fats are solids at room temperature while oils are liquids. Secondly, fats occur naturally in animal tissue, while oils occur naturally in plant tissue. Human body fat is a good example of this type of lipids. Fat cells, also called adipose cells, store away fat energy until the time comes when the body needs it, according to "Biology" by Campbell, Reece and Mitchell.

    Phospholipids

    • Phospholipids resemble fats in their chemical structure. But while fats have only carbon, hydrogen and a little oxygen in their composition, phospholipids have the additional element of phosphorus. While fats are completely insoluble in water, one end of the phospholipid molecule is attracted to water, while the other end is repelled by water, so that phospholipids are more soluble in water than fats. Phospholipids are important structural components in the tissues of both plants and animals. The basic unit of plant and animal tissue is the cell, and all cells are surrounded by a protective membrane. Phospholipids are the principal material in these membranes.

    Steroids

    • Steroids have a more complicated structure than the other two types of lipids. All steroids have the same fundamental skeleton: Four rings of carbon atoms joined together to form a single unit. Many steroids are hormones that have powerful effects on the body. Testosterone, for example, causes boys to start growing beards when they reach puberty, and at the same time, it dramatically lowers the pitch of their voices. Estrogen and progesterone, female sex hormones, are also steroids. The well-known cholesterol is also a steroid. It serves as a structural component in body tissues. It also serves as the raw material from which the body makes other steroids, such as testosterone.

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