pls explain the structure of lipids simply?

Although lipid analyst tend to have a firm understanding of what is meant by the term "lipid", there is no widely-accepted definition. General text books usually describe lipids in woolly terms as a group of naturally occurring compounds, which have in common a ready solubility in such organic solvents as hydrocarbons, chloroform, benzene, ethers and alcohols. They include a diverse range of compounds, like fatty acids and their derivatives, carotenoids, terpenes, steroids and bile acids. It should be apparent that many of these compounds have little by way of structure or function to relate them. In fact, a definition of this kind is positively misleading, since many of the substances that are now widely regarded as lipids may be almost as soluble in water as in organic solvents.

Although lipid analyst tend to have a firm understanding of what is meant by the term "lipid", there is no widely-accepted definition. General text books usually describe lipids in woolly terms as a group of naturally occurring compounds, which have in common a ready solubility in such organic solvents as hydrocarbons, chloroform, benzene, ethers and alcohols. They include a diverse range of compounds, like fatty acids and their derivatives, carotenoids, terpenes, steroids and bile acids. It should be apparent that many of these compounds have little by way of structure or function to relate them. In fact, a definition of this kind is positively misleading, since many of the substances that are now widely regarded as lipids may be almost as soluble in water as in organic solvents.

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 The lipid group includes:

Fatty acids

Most fatty acids in cells are linked to other molecules. They are either saturated or unsaturated fatty acids. In both cases, the hydrocarbon chain is unbranched.In unsaturated fatty acids, at least two and no more than six carbon atoms in the hydrocarbon chain are linked together by double bonds.

Triglycerides

A triglyceride consists of a glycerol and three fatty acids. It is the major type of lipid used for energy storage and it is found in droplets within the cytoplasm. It is non-polar and relatively insoluble. Triglycerides are divided into two groups dependent on their state at 20 oC; if they are solid at this temperature, they are called fats and if they are liquid, they are called oils. The higher the proportion of unsaturated fatty acids in the triglyceride the lower its melting point. Triglycerides are less dense than water, therefore they float.

Phospholipids

Phospholipids are lipids containing a phosphate group, they are found in cellular membranes.

Glycolipids

Glycolipids are lipids with short chains of sugar attached to them. They are commonly found in cellular membranes. They are involved in the immune system and cell-to-cell recognition.

Waxes

Waxes are esters of fatty acids combined with long chain alcohols. Waxes are mainly used as a waterproofing material by plants and animals, e.g. on leaves of plants and on the feathers of animals.

Lipoproteins

Lipoproteins are combinations of lipids and proteins, they are found in membranes. When lipids are transported through the blood and lymphatic systems, they are in the form of lipoproteins.

Steroids

Steroids do not contain fatty acids. Steroids have widely different physiological properties. Hormones such as oestrogen are steroids, as are vitamins such as D2. Steroids are constituents of the plasma membrane, influencing the membrane’s structure and its role in transport and permeability. The most well known plasma membrane steroid is cholesterol.

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