6. Biomolecules - part 02 - Lipids
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6. Biomolecules - part 02 - Lipids
B. Lipids :
- These are group of substances with greasy consistency with long hydrocarbon chain containing carbon, hydrogen and oxygen.
- In lipids, hydrogen to oxygen ratio is greater than 2:1 (in carbohydrates it is always 2:1).
- Lipid is a broader term used for fatty acids and their derivatives.
- They are soluble in organic solvents (non-polar solvents).
- Fatty acids are organic acids which are composed of hydrocarbon chain ending in carboxyl group (-COOH).
- They can be saturated fatty acids with no double bonds between the carbon atoms of the hydrocarbon chain.
- Palmitic and stearic acids found in all animal and plant fats are examples of saturated fatty acids.
- Unsaturated Fatty Acids are with one or more double bonds between the carbon atoms of the hydrocarbon chain.
- Oleic acid found in nearly all fats and linoleic acid found in many seed oils are examples of unsaturated fatty acids.
- These fatty acids are basic molecules which form different kinds of lipids.
- simple lipids
- compound lipids
- derived lipids.
1. Simple Lipids :
- These are esters of fatty acids with various alcohols.
- Simple lipids are-
- Fats and
- waxes
- Fats are esters of fatty acids with glycerol (CH2OH-CHOH-CH2OH).
- Triglycerides are three molecules of fatty acids and one molecule of glycerol.
- Generally, unsaturated fats are liquid at room temperature and are called oils. Unsaturated fatty acids are hydrogenated to produce fats e.g. Vanaspati ghee.
- Fats are a nutritional source with high calorific value.
- Fats act as reserved food materials.
- In plants it is stored in seeds to nourish embryo during germination.
- In animals fat is stored in the adipocytes of the adipose tissue.
- Fats deposited in subcutaneous tissue act as an insulator and minimise loss of body heat.
- Fats deposited around the internal organs act as cushions to absorb mechanical shocks.
- Wax is another example of simple lipid.
- They are esters of long chain fatty acids with long chain alcohols.
- They are most abundant in the blood, the gonads and the sebaceous glands of the skin.
- Waxes are not as readily hydrolysed as fats.
- They are solid at ordinary temperature.
- Waxes form water insoluble coating on hair and skin in animals, waxes form an outer coating on stems, leaves and fruits.
2. Compound lipids :
- These are ester of fatty acids containing other groups like phosphate (Phospholipids), sugar (glycolipids), etc.
- They contain a molecule of glycerol, two molecules of fatty acids and a phosphate group or simple sugar.
- Some phospholipids such as lecithin also have a nitrogenous compound attached to the phosphate group.
- Phospholipids have both hydrophilic polar groups (phosphate and nitrogenous group) and hydrophobic non-polar groups (hydrocarbon chains of fatty acids).
- Phospholipids contribute in the formation of cell membrane.
- Glycolipids contain glycerol, fatty acids, simple sugars such as galactose and nitrogenous base. They are also called cerebrosides.
- Large amounts of them have been found in the brain white matter and myelin sheath.
3. Sterols - derived lipids :
- They are derived lipids.
- They are composed of fused hydrocarbon rings (steroid nucleus) and a long hydrocarbon side chain.
- One of the most common sterol is cholesterol.
- It is widely distributed in all cells of the animal body, but particularly in nervous tissue.
- Cholesterol exists either free or as cholesterol ester.
- Adrenocorticoids, sex hormones (progesterone, testosterone) and vitamin D are synthesised from cholesterol.
- Cholesterolis not found in plants.
- In plants, sterols existchiefly as Phytosterols.
- Yam Plant (Dioscorea) produces a steroid compound called diosgenin.
- It is used in the manufacture of antifertility pills. i.e. birth control pills.
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