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Fats form a category of lipid, distinguished from other lipids by their chemical structure and physical properties. Fats are solid at room temperature as opposed to oils which are liquid. 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).

Chemical structure

Chemical structure of trimyristin, a triglyceride.

There are many different kinds of fat, but each kind is a variation on the same chemical structure. All fats consist of fatty acids (chains of carbon and hydrogen atoms, with an oxygen atom at one end and occasionally other molecules) bonded to a backbone structure, often glycerol (a "backbone" of carbon, hydrogen, and oxygen). Chemically, this is a triester of glycerol, being the molecule formed from the reaction of an acid and an alcohol. 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. Fats have "ester" bonds.

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 are more susceptible to intermolecular forces of attraction (in this case, van der Waals forces), raising its melting point. Long chains also yield 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; meaning they are bonded to as many hydrogens as they possibly could be. In other fats, a carbon atom may instead bond to only one other hydrogen atom, and have a double bond to 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, and a fat containing more than one unsaturated fatty acid is called polyunsaturated.

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 fundamentally changes the chemistry of the fat. There are two ways the double bond may be arranged: the isomer with the both parts of the chain on the same side of the double bond (the cis-isomer; also the only naturally occuring type of fat), or the isomer with the parts of the chain on opposite sides of the double bond (the trans-isomer, generally a product of partial hydrogenation of natural unsaturated fats). The cis-isomer introduces a kink into the molecule that prevents the fats from stacking efficiently like with saturated chains. This decreases intermolecular forces between the fat molecules, making it more difficult for unsaturated cis-fats to freeze; they are typically liquid at room temperature. Trans-fats, however, may still stack like saturated fats, but are not as susceptible to metabolization. Trans-fats have been associated with many health problems, but their biochemistry is poorly understood.

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 are also known as lipids. 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. The exact method varies on what type of fat you are analyzing, for example, polyunsaturated and monounsaturated fats are tested quite differently.

Adipose tissue

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.

Metabolism

Lipids are an excellent source of energy, and are used by the body as a direct source of energy as well as a way of storing energy. 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 overweight people are more sensitive to pain, particulairly in their abdominal region.

References

Rebecca J. Donatelle. Health, The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.

External links

Chemical Structure of Fats and Fatty acids

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 '''Fats''' form a category of [[lipid]], distinguished from other lipids by their [[chemical structure]] and physical properties. Fats are solid at room temperature as opposed to oils which are liquid. 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 [[heterotroph]]s (including humans).
+==Chemical structure==
+[[Image:Trimyristin.png|thumb|right|100px|Chemical structure of [[trimyristin]], a triglyceride.]]
+There are many different kinds of fat, but each kind is a variation on the same chemical structure.  All fats consist of [[fatty acid]]s (chains of [[carbon]] and [[hydrogen]] atoms, with an [[oxygen]] atom at one end and occasionally other molecules) bonded to a backbone structure, often [[glycerol]] (a "backbone" of carbon, hydrogen, and oxygen). Chemically, this is a [[ester|triester]] of glycerol, being the molecule formed from the reaction of an acid and an alcohol. As a simple visual illustration, if the kinks and [[bond angle|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. Fats have "ester" [[bonds]].
+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 are more susceptible to intermolecular forces of attraction (in this case, [[van der Waals forces]]), raising its [[melting point]]. Long chains also yield 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 [[saturation|"saturated"]], because the carbon atoms are saturated with hydrogen; meaning they are [[covalent bond|bonded]] to as many hydrogens as they possibly could be.  In other fats, a carbon atom may instead bond to only one other hydrogen atom, and have a [[double bond]] to 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, and a fat containing more than one unsaturated fatty acid is called polyunsaturated.
+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 fundamentally changes the chemistry of the fat. There are two ways the double bond may be arranged: the isomer with the both parts of the chain on the same side of the double bond (the ''[[cis]]''-isomer; also the only naturally occuring type of fat), or the isomer with the parts of the chain on opposite sides of the double bond (the ''[[trans]]''-isomer, generally a product of partial hydrogenation of natural unsaturated fats). The ''cis''-isomer introduces a kink into the molecule that prevents the fats from stacking efficiently like with saturated chains. This decreases intermolecular forces between the fat molecules, making it more difficult for unsaturated cis-fats to freeze; they are typically liquid at room temperature. [[Trans-fats]], however, may still stack like saturated fats, but are not as susceptible to metabolization. Trans-fats have been associated with many health problems, but their biochemistry is poorly understood.
 ==Importance for living things==
-[[jhFats play a vital role in maintaining healthy [[skin]] and [[hair]], insulating body organs against shock, maintaining body temperature, and promoting healthy cell function. They are also known as lipids. They also serve as energy stores for the body.  Fats are broken down in the body to release [[Glycerin|glycerol]] and free [[fatty acid]]s.  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.
+[[Vitamin]]s [[Vitamin A|A]], [[Vitamin D|D]], [[Vitamin E|E]], and [[Vitamin K|K]] are fat-soluble, meaning they can only be digested, absorbed, and transported in conjunction with fats. Fats are sources of [[essential fatty acid]]s, 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 are also known as lipids. They also serve as energy stores for the body.  Fats are broken down in the body to release [[Glycerin|glycerol]] and free [[fatty acid]]s.  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. The exact method varies on what type of fat you are analyzing, for example, polyunsaturated and monounsaturated fats are tested quite differently.