Saturday, December 7, 2013

Lipids and Examples of lipids

Lipids are fatty, oily, or waxy organic compounds. Lipids are a structurally heterogeneous class of biological molecules that are, as their common characteristic, hydrophobic. Which means that they are insoluble in water. The building blocks of lipids are fatty acids and glycerol. Lipids posses numerous C-H bonds (i.e., they are very hydrocarbon-like). Examples of lipids include: (i) Fats, (ii) Oils, (iii) Waxes, (iv) Phospholipids, and (v) Steroids, etc.
Lipids are similar to carbohydrates in that they contain only carbon, hydrogen, and oxygen. They differ from carbohydrates in one important way: no specific ratio (C:H:O). Many also serve as source of energy. In fact, a gram of fat can produce over twice as much energy as a gram of carbohydrate. Lipids are also a storage form of energy. The proportion of hydrogen to oxygen in carbohydrates is two to one. In lipid it is much higher.

Fats and oils

Fats are lipids with one, two, or three long chain fatty acids bonded (called an ester linkage) to a small alcohol called glycerol. When three fatty acids attach to a glycerol, the resulting molecule, which is called a triglyceride, is entirely hydrophobic.
Fatty acids are long-chain hydrocarbons with a carboxyl group (-COOH) at one end.
Fatty acids can be saturated or unsaturated. Saturated types have only single bonds in their tails. In other words, their carbon chains are fully saturated with hydrogen atoms. Saturated fatty acids have no C=C double bonds. Unsaturated fatty acids have one or more C=C double bonds. The tails of unsaturated fatty acids have one or more double bonds that limit their flexibility. Increasing the unsaturation of a fatty acid results in a decreasing melting point.
Fats and oils possess more energy per molecule and less hydration compared with carbohydrates, resulting in fats or oils possessing much more energy stored per unit mass or volume. During digestion, the fat or oil is broken down into these simple molecules (monomers). Fats and oils function in biological systems as energy storage molecules (e.g., nuts, seeds, and animals).
1.Saturated fatty acids have no C=C double bonds. eg. Octanoic acid
2. Unsaturated fatty acids have one or more C=C double bonds. eg. 3-octanoic acid
3. Increasing the unsaturation of a fatty acid results in a decreasing melting point. eg, 3,6-octanoic

Fats are solid at ordinary temperatures. Generally, fats are produced by animals. In animals, fats are stored in adipose cells. Fats are also important as cushions for body organs and as an insulating layer beneath skin.


Oils are liquid at ordinary temperatures. Generally, oils are produced by plants. Some common vegetable oils are peanut, soybean, and corn oil.

Both plants and animals produce waxes. The waxy coating on some plants leaves is an example of plant waxes. Beeswax is an example of a wax produced by an animal.

Phospholipids & Steroids

Phospholipids differ from triacylglycerol in the sense that, one fatty acid (out of three) is replaced with a phosphate group, which in turn is bound to additional functional groups.
Structurally and functionally, the important thing about phospholipids is that these molecules are simultaneously hydrophobic (at one end, thefatty acid end) and hydrophilic (at the other end, the phosphate end). Phospholipids are the most abundant lipids in cell membranes, which have two layers of lipids.

Steroids are lipids with a rigid backbone of four carbon rings and no fatty acid tails. All steroids possess a common ring structure. These ring structures vary by attached functional groups. Cholesterol is example of a steroid; cholesterol is a membrane component. The common steroid structure is the basis of sterol hormones including the human sex hormones (the estrogens and the androgens, including testosterone).