Fat

From Free net encyclopedia

This article is about lipid molecules. Fat may also refer to obesity or adipose tissue. FAT is an acronym.

Fats form a category of lipid, distinguished from other lipids by their chemical structure. This category of molecules is important for many forms of life, serving both structural and metabolic functions. They are an important part of the diet of most heterotrophs (including humans).

1 Chemical structure
2 Importance for living things
3 Energy
4 Adipose tissue
5 Metabolism
6 See also
7 References
8 External links

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Chemical structure

Image:Trimyristin.png There are many different kinds of fat, but each kind is a variation on the same chemical structure. All fats consist of three fatty acids (chains of carbon and hydrogen atoms, with an oxygen atom at one end) bonded to glycerol (a "backbone" of carbon, hydrogen, and oxygen). As a simple visual illustration, if the kinks and angles of these chains were straightened out, the molecule would have the shape of a capital letter E. The fatty acids would each be a horizontal line; the glycerol "backbone" would be the vertical line that joins the horizontal lines.

The properties of any specific fat molecule depend on the particular fatty acids that help to make it up. Different fatty acids are comprised of different numbers of carbon and hydrogen atoms. The carbon atoms, each bonded to two neighboring carbon atoms, form a zigzagging chain; the more carbon atoms there are in any fatty acid, the longer its chain will be. Fatty acids with long chains make the fat they are a part of more massive, raising its melting point and yielding more energy per molecule when metabolized.

A fat's constituent fatty acids may also differ in the number of hydrogen atoms that branch off of the chain of carbon atoms. Each carbon atom is typically bonded to two hydrogen atoms. When a fatty acid has this typical arrangement, it is called "saturated", because the carbon atoms are saturated with hydrogen. They are bonded to as much hydrogen as they possibly could be. Occasionally, though, a carbon atom may instead bond to only one other hydrogen atom, and have a double bond with a neighboring carbon atom. This results in an "unsaturated" fatty acid. A fat containing only saturated fatty acids is itself called saturated. A fat containing at least one unsaturated fatty acid is called unsaturated.

Saturated and unsaturated fats differ in their energy content and melting point. Since an unsaturated fat contains fewer carbon-hydrogen bonds than a saturated fat with the same number of carbon atoms, unsaturated fats will yield slightly less energy during metabolism than saturated fats with the same number of carbon atoms. Saturated fats can stack themselves in a closely packed arrangement, so they can freeze easily and are typically solid at room temperature. But the rigid double bond in an unsaturated fat introduces a kink in the fatty acid chain that makes it more difficult for their fat molecules to arrange together. This makes it more difficult for unsaturated fats to freeze; they are typically liquid at room temperature.

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Importance for living things

Vitamins A, D, E, and K are fat-soluble, meaning they can only be digested, absorbed, and transported in conjunction with fats. Fats are sources of essential fatty acids, an important dietary requirement.

Fats play a vital role in maintaining healthy skin and hair, insulating body organs against shock, maintaining body temperature, and promoting healthy cell function. They also serve as energy stores for the body. Fats are broken down in the body to release glycerol and free fatty acids. The glycerol can be converted to glucose by the liver and thus used as a source of energy. The fatty acids are a good source of energy for many tissues, especially heart and skeletal muscle.

The fat content of a food can be analyzed by extraction.

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Energy

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Adipose tissue

Template:Main Adipose, or fatty tissue is the human body's means of storing metabolic energy over extended periods of time. Depending on current physiological conditions, adipocytes store fat derived from the diet and liver metabolism or degrades stored fat to supply fatty acids and glycerol to the circulation. These metabolic activities are regulated by several hormones (i.e., insulin, glucagon and epinephrine). The location of the tissue determines its metabolic profile: "Visceral fat" (around the abdomen) is prone to lead to insulin resistance, while "peripheral fat" (around the limbs) is much more harmless.

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Metabolism

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The metabolism of lipids is a closely regulated system in virtually all lifeforms. It is affected by a variety of enzymes and, in higher organisms, regulated by hormones. Research is ongoing on the relative influence of various hormonal regulators on the anabolism (production) and catabolism (breakdown, also termed lipolysis) of fatty molecules.

A subject of particularly close study is cholesterol, levels and types of which are influenced by the fatty acid metabolism and is known for its role in development of nerve cells atherosclerosis. Thus the suggesting that fat people are more sensitive to pain, particulairly in their abdominal region.

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