Lipid is one of a large group of oily or fatty substances essential for good health. Lipids, carbohydrates, and proteins are the classes of compounds in all living things. Animal fats and plant oils are lipids. So are animal sex hormones and vitamins A, D, E, and K. Egg yolks, liver, and embryos of grains are rich in lipids.
Importance of lipids.
Lipids are vital to animals and plants in many ways. They are a concentrated source of food energy and yield about twice as many calories as an equal weight of protein or carbohydrate. Many kinds of organisms store food in lipid form. For example, the seeds of many plants contain lipids as food reserves for their embryos. The bone marrow, tissues beneath the skin and in the intestines, and tissue surrounding body organs in animals consist mostly of stored lipids.
Certain lipids form an essential part of the membranes that enclose and protect every living cell. Similar membranes surround all bodies within the cell, so that each cell body can do its job without unwanted interference from other cell bodies. Lipids repel water, but they are valuable solvents (dissolving substances) for vitamins A, D, E, and K, which do not dissolve in water.
Kinds of lipids.
Lipids are classified as simple lipids or complex lipids, according to their structure.
Simple lipids contain only carbon, hydrogen, and oxygen. They consist of an alcohol in combination with certain organic acids containing a variable number of carbon atoms. A molecule of triglyceride (fat), the most common type of simple lipid, contains one molecule of an alcohol called glycerol and three molecules of fatty acid (a kind of organic acid). Fats include butter, lard (pig fat), tallow (beef or mutton fat), blubber (whale fat), castor oil, coconut oil, and olive oil. Waxes, another common group of simple lipids, contain an alcohol molecule that is larger than the glycerol molecule.
Complex lipids have a more complicated structure than simple lipids. They include phospholipids (lipids that contain phosphorus), steroids (lipids made up of four rings of carbon atoms joined together), and other compounds such as glycolipids (lipids with one or more sugar molecules), fat-soluble vitamins (vitamins A, D, E, and K), and terpenes (yellow pigments like carotene).
Phospholipids are found in all bacteria, and in the cells of all plants and animals. They are most plentiful in sperm, eggs, embryos, and brain cells. A molecule of phospholipid contains a molecule of glycerol, a phosphate ion, and two molecules of fatty acid. Most phospholipids also have a nitrogen compound. Some contain inositol, a substance found in vitamin B complex.
Steroids make up an important part of living things. Many animal hormones, including the sex hormones and those produced by the cortex (outer part) of the adrenal glands, are steroids. Cholesterol, a substance found in the membranes of animal cells, is a steroid. Yeasts and other fungi and the seeds of higher plants also contain steroids.
Importance of lipids.
Lipids are vital to animals and plants in many ways. They are a concentrated source of food energy and yield about twice as many calories as an equal weight of protein or carbohydrate. Many kinds of organisms store food in lipid form. For example, the seeds of many plants contain lipids as food reserves for their embryos. The bone marrow, tissues beneath the skin and in the intestines, and tissue surrounding body organs in animals consist mostly of stored lipids.
Certain lipids form an essential part of the membranes that enclose and protect every living cell. Similar membranes surround all bodies within the cell, so that each cell body can do its job without unwanted interference from other cell bodies. Lipids repel water, but they are valuable solvents (dissolving substances) for vitamins A, D, E, and K, which do not dissolve in water.
Kinds of lipids.
Lipids are classified as simple lipids or complex lipids, according to their structure.
Simple lipids contain only carbon, hydrogen, and oxygen. They consist of an alcohol in combination with certain organic acids containing a variable number of carbon atoms. A molecule of triglyceride (fat), the most common type of simple lipid, contains one molecule of an alcohol called glycerol and three molecules of fatty acid (a kind of organic acid). Fats include butter, lard (pig fat), tallow (beef or mutton fat), blubber (whale fat), castor oil, coconut oil, and olive oil. Waxes, another common group of simple lipids, contain an alcohol molecule that is larger than the glycerol molecule.
Complex lipids have a more complicated structure than simple lipids. They include phospholipids (lipids that contain phosphorus), steroids (lipids made up of four rings of carbon atoms joined together), and other compounds such as glycolipids (lipids with one or more sugar molecules), fat-soluble vitamins (vitamins A, D, E, and K), and terpenes (yellow pigments like carotene).
Phospholipids are found in all bacteria, and in the cells of all plants and animals. They are most plentiful in sperm, eggs, embryos, and brain cells. A molecule of phospholipid contains a molecule of glycerol, a phosphate ion, and two molecules of fatty acid. Most phospholipids also have a nitrogen compound. Some contain inositol, a substance found in vitamin B complex.
Steroids make up an important part of living things. Many animal hormones, including the sex hormones and those produced by the cortex (outer part) of the adrenal glands, are steroids. Cholesterol, a substance found in the membranes of animal cells, is a steroid. Yeasts and other fungi and the seeds of higher plants also contain steroids.
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