LIPIDS
Discovered by bloor in1943.Lipids are heterogeneous group of compounds that include fats and oils. Lipids are macromers of fatty acids. As they are non-polar molecules, most lipids are insoluble in water but soluble in non-polar solvents such as alcohol and ether.
Important exceptions are phospholipids, which have polar heads. Lipids contain the elements carbon, hydrogen, oxygen and sometimes phosphorus and nitrogen. Lipids contain double amount of energy than that of carbohydrates and protein.
They are intermediate-sized molecules that do not achieve the giant sizes of the polysaccharides, proteins and nucleic acids.
LIPID STRUCTURE AND FUNCTION:
The triglycerides, which act mainly as energy stores in animals and plants, are a large important group of lipids. Triglycerides consist of one molecule of glycerol and three fatty acids.
The glycerol molecule is common to all triglycerides and so the properties of different triglycerides depend on the nature of the fatty acids.Monounsaturated fatty acids possess one C=C bond and polyunsaturated nsaturated contain more than one while saturated do not contain any double bond.Saturated are solid at room temperature while unsaturated are liquid at ordinary temperature.
Types of lipids
PHOSPHOLIPIDS:
Phospholipids are derivatives of phosphatidic acid. The phosphatidic acid is composed of glycerol, fatty acids and phosphoric acid. Phosphatidylcholine is one of the common phospholipids. Phospholipids have a similar structure to triglycerides but one of the fatty acids IS replaced by polar phosphoric acid.
This gives the molecule a polar head and a non-polar tail. When placed in water, phospholipids arrange themselves with their hydrophobic (water-hating) tails pointing inwards and their hydrophilic (water-loving) heads pointing outwards. This is very important because it results in double layers called bilayers. Phospholipid bilayers form the basis of all biological membranes.
CHOLESTEROL:
It produces flexibility in cell membrane. This lipid is a normal component of every cell in our body. As well as eating food that contains cholesterol, we can also synthesis cholesterol in the liver.
The more there is in the diet the less the liver needs to make. Vegetarians who eat no animal products are easily able to make all the cholesterol they need.
STEROID HORMONES:
Steroid hormones have a similar structure to the cholesterol from which they are made. They include testosterone, progesterone and the estrogens.
WAXES:
Waxes are lipids that are often used to waterproof surface, so preventing water loss. The cuticle of a leaf and the protective covering on an insect's body are both waxes. Waxes are mixtures of long chain alkanes (C25 to C35 odd numbers), alcohols, ketones and esters of long chain fatty acids.They have no nutritionl value because they cannot be digested by lipases (lipid digesting enzymes).