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The molecular structures of alpha-linolenic acid, an omega-3 fatty acid is shown. Alpha-linolenic acid has three double bonds located eight, eleven, and fourteen residues from the acetyl group. It has a hooked shape.
Alpha-linolenic acid is an example of an omega-3 fatty acid. It has three cis double bonds and, as a result, a curved shape. For clarity, the carbons are not shown. Each singly bonded carbon has two hydrogens associated with it, also not shown.

The farthest carbon away from the carboxyl group is numbered as the omega ( ω ) carbon, and if the double bond is between the third and fourth carbon from that end, it is known as an omega-3 fatty acid. Nutritionally important because the body does not make them, omega-3 fatty acids include alpha-linoleic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), all of which are polyunsaturated. Salmon, trout, and tuna are good sources of omega-3 fatty acids. Research indicates that omega-3 fatty acids reduce the risk of sudden death from heart attacks, reduce triglycerides in the blood, lower blood pressure, and prevent thrombosis by inhibiting blood clotting. They also reduce inflammation, and may help reduce the risk of some cancers in animals.

Like carbohydrates, fats have received a lot of bad publicity. It is true that eating an excess of fried foods and other “fatty” foods leads to weight gain. However, fats do have important functions. Many vitamins are fat soluble, and fats serve as a long-term storage form of fatty acids: a source of energy. They also provide insulation for the body. Therefore, “healthy” fats in moderate amounts should be consumed on a regular basis.

Waxes

Wax covers the feathers of some aquatic birds and the leaf surfaces of some plants. Because of the hydrophobic nature of waxes, they prevent water from sticking on the surface ( [link] ). Waxes are made up of long fatty acid chains esterified to long-chain alcohols.

The photo shows leaves on a plant; the leaves appear thick, shiny, and waxy.
Waxy coverings on some leaves are made of lipids. (credit: Roger Griffith)

Phospholipids

Phospholipids are major constituents of the plasma membrane, the outermost layer of animal cells. Like fats, they are composed of fatty acid chains attached to a glycerol or sphingosine backbone. Instead of three fatty acids attached as in triglycerides, however, there are two fatty acids forming diacylglycerol, and the third carbon of the glycerol backbone is occupied by a modified phosphate group ( [link] ). A phosphate group alone attached to a diaglycerol does not qualify as a phospholipid; it is phosphatidate (diacylglycerol 3-phosphate), the precursor of phospholipids. The phosphate group is modified by an alcohol. Phosphatidylcholine and phosphatidylserine are two important phospholipids that are found in plasma membranes.

The molecular structure of a phospholipid is shown. It consists of two fatty acids attached to the first and second carbons in glycerol, and a phosphate group attached to the third position. The phosphate group may be further modified by addition of another molecule to one of its oxygens. Two molecules that may modify the phosphate group, choline and serine, are shown. Choline consists of a two-carbon chain with a hydroxy group attached to one end and a nitrogen attached to the other. The nitrogen, in turn, has three methyl groups attached to it and has a charge of plus one. Serine consists of a two-carbon chain with a hydroxyl group attached to one end. An amino group and a carboxyl group are attached to the other end.
A phospholipid is a molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone. The phosphate may be modified by the addition of charged or polar chemical groups. Two chemical groups that may modify the phosphate, choline and serine, are shown here. Both choline and serine attach to the phosphate group at the position labeled R via the hydroxyl group indicated in green.

A phospholipid is an amphipathic molecule, meaning it has a hydrophobic and a hydrophilic part. The fatty acid chains are hydrophobic and cannot interact with water, whereas the phosphate-containing group is hydrophilic and interacts with water ( [link] ).

Questions & Answers

Give tow examples for nutritional deficiency Diseases-
Singampalli Reply
How does a plant cell look like
Sang Reply
in a sleepers form
David
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Gul
a stage in mitosis wherein in spindle fibers begin to shorten to pu the sister chromatids away from each other towards the opposite ends of the cell
Earl Reply
a stage in interphase where chromosome s are duplicated
Earl
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Sp Reply
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Hele
Name two secretions of Golgi apparatus
Daniel Reply
What contribute to evolution of eukaryotes
Chiquita Reply
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Nubia
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surya
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Sajid Reply
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Faith Reply
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Majid Reply
any of a class of nitrogenous organic compounds which have large molecules composed of one or more long chains of amino acids and are an essential part of all living organisms, especially as structural components of body tissues such as muscle, hair, etc., and as enzymes and antibodies.
Anirban
what is DNA replication?
Anirban Reply
separation of the DNA to produce new daughter cell. mostly in the form of meiosis
Faith
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Mani Reply
can i get a broader difference between inductive reasoning and deductive reasoning
Daniel Reply
what are the types of tissues and there functions
Daniel
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nur Reply
it is the process by which plants produce their fo
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what are the substrates of this process
Fiko
definition of photosynthesis
Fiko Reply
it is simply the process by which plants get there food from the sun through the use of chlorophyll
Daniel

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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