Lipids


Image Caption : Fats Within the Bloodstream : Bloodstream is the blood flowing through the circulatory system. Blood is watery, and cholesterol is fatty. Just like oil and water, the two do not mix. To travel in the bloodstream, cholesterol is carried in small packages called lipoproteins. Too much cholesterol in the blood, or high blood cholesterol, can be serious. People with high blood cholesterol have a greater chance of getting heart disease. High blood cholesterol on its own does not cause symptoms, so many people are unaware that their cholesterol level is too high.

Lipids

A generic term for fats and lipoids, the alcohol-ether-soluble constituents of protoplasm, which are insoluble in water. They comprise the fats, fatty oils, essential oils, waxes, phospholipids, glycolipids, sulfolipids, aminolipids, chromolipids (lipochromes), and fatty acids.

National Center for Biotechnology Information, U.S. National Library of Medicine.

  • Triglyceridesare the main components of vegetable oils and animal fats. They’re made up of three fatty acid molecules attached to one glycerol molecule. Triglycerides are broken down in your digestive system so that those fatty acids can be burned for energy. Any excess triglycerides are stored in your fat cells.
  • Phospholipidscontain two fatty acids and have a head region and a tail region. The head is hydrophilic—attracted to water. The tail is hydrophobic—repelled by water. Phospholipids arrange themselves into double-layered membranes. The outside surfaces of these membranes contain the heads of the phospholipids and are hydrophilic.
  • Cholesterolhas a bad reputation, but the fact is you couldn’t live without it. It’s made by all the cells in your body and forms up to half of the cell membrane. Cholesterol helps to make vitamin D. It’s used to create bile acids, which you must have in order to absorb dietary fats. And cholesterol is a building block for many hormones, including the sex hormones estrogen and testosterone.

Your bloodstream carries nutrients, such as lipids, to your cells. But there’s a problem: Because blood is mostly water, lipids and blood won’t mix. To move freely through your blood vessels, lipids must be carried by lipoproteins—spherical particles made up of lipids and proteins. Lipoprotein particles are held together by a phospholipid membrane arranged so that the hydrophilic side faces outward. This allows the lipoprotein particles to mix with your blood and sail through your bloodstream like ships, carrying their cargos of lipids.

Lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, phospholipids, and others. The main biological functions of lipids include storing energy, signaling, and acting as structural components of cell membranes. Lipids have applications in the cosmetic and food industries as well as in nanotechnology.

Lipids may be broadly defined as hydrophobic or amphiphilic small molecules; the amphiphilic nature of some lipids allows them to form structures such as vesicles, multilamellar/unilamellar liposomes, or membranes in an aqueous environment. Biological lipids originate entirely or in part from two distinct types of biochemical subunits or "building-blocks": ketoacyl and isoprene groups. Using this approach, lipids may be divided into eight categories: fatty acids, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids, and polyketides (derived from condensation of ketoacyl subunits); and sterol lipids and prenol lipids (derived from condensation of isoprene subunits).

Although the term lipid is sometimes used as a synonym for fats, fats are a subgroup of lipids called triglycerides. Lipids also encompass molecules such as fatty acids and their derivatives (including tri-, di-, monoglycerides, and phospholipids), as well as other sterol-containing metabolites such as cholesterol. Although humans and other mammals use various biosynthetic pathways both to break down and to synthesize lipids, some essential lipids cannot be made this way and must be obtained from the diet.


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