Lipids : Term lipid was coined by Bloor. These are esters of fatty acids and alcohol. They are hydrophobic insoluble in water but soluble in benzene, ether and chloroform. Lipids are classified into three groups:–
lkjhg(i) Simple lipids : These are the esters of fatty acids and glycerol. Again they are typed as :–
# (a) Fats and Oils : (Natural lipids or true fats). These triglycerides of fatty acid and glycerol. Fats which are liquid at room temperature are called oils. Oils with polyunsaturated fatty acids are called polyunsaturated e.g. sunflower oil, lower blood cholesterol.
# (b) Fatty acids : Obtained by hydrolysis of fats. Formic acid is simplest fatty acid (HCOOH). These are of 2 types :–
Saturated fatty acids : The fatty acids which do not have double bond in between carbon atoms.e.g. butyric acid, palmitic acid,hexanoic acid, etc. They have high melting points, solid at room temperature and increase blood cholesterol.
Unsaturated fatty acids : The fatty acids which have double bonds in carbon atoms. e.g. 8 hexadecanoic acid, 9 octadecanoic acid etc. They have lower melting points mostly found in plant fats, liquid at room temperature and lower the blood cholesterol.
# (c) Waxes : These are simple lipids composed of one molecule of long chain fatty acid and long chain monohydric alcohol. Waxes have high melting point, insoluble in water, resistant to atmospheric oxidation, chemically inert and not digested by enzymes. They reduce rate of transpiration by making plant tissue water proof and work as excellent lubricant.
Types of waxes
Plant wax : Forms coating.
Bee's wax : It is secretion of abdominal glands of worker honeybee. It consist of palmitic acid and myricyl alcohol.
Lanolin or Wool fat : It is secreted by cutaneous glands, also obtained from wool of sheeps. It consists of palmitic acid, oleic or stearic acid and cholesterol.
Sebum : It is secretion of sebaceous gland of skin.
Paraffin wax : Obtained from petrolium.
(ii) Compound lipids : They contain some additional or element. Group with fatty acid and alcohol on the basis of group they may be of following types:
# (a) Phospholipids : These contain phosphoric acid. It helps in transport, metabolism, blood clotting and permeability of cell membrane. It is a bipolar molecule i.e. phosphate containing end is hydrophilic whereas fatty acid molecules represent hydrophobic (non-polar tail). Phospholipids again comprises.
- Lecithin : These are yellowish grey solids, soluble in ether and alcohol but insoluble in acetone. On hydrolysis they yield glycerol, fatty acid, phosphoric acid and choline. Lecithins are broken down by enzyme lecithinase to lysolecithin. The enzyme is found in venom of bee and cobra.
- Cephalins : Found in animal tissue and soyabean oil. Cephalin contains choline or serine sometimes and stearic acid, oleic acid, linoelic and arachidonic acid.
# (b) Glycolipids : These contain nitrogen and carbohydrate beside fatty acids. Generally found in white matter of nervous system. e.g. sesocine frenocin.
# (c) Chromolipids : It includes pigmented lipids e.g. carotene.
# (d) Aminolipids : Also known as sulpholipids. It contains sulphur and amino acids with fatty acid and glycerol. Cutin and suberin are also compound lipids resistant to water and also provide mechanical support in plants.
(iii) Derived lipids : These are obtained by hydrolysis of simple and compound lipids. Derived lipids include following components :–
# (a) Sterols : Lipids without straight chains are called sterols. They are composed of fused hydrocarbon rings and a long hydrocarbon side chain. Best known sterol is cholesterol, present in high concentration in nervous tissue and in bile. Cholesterol is also the precursor of hormones like progesterone, testosterone, estradiol and cortisol and vitamin D. Diosgenin is obtained from yam plant (Dioscorea) used in making anti- infertility pills.
# (b) Digitalin : It is prepared from leaves of Foxglove (Digitalis lantana) is a heart stimulant.
# (c) Ergosterol : Present in food, found in ergot and yeast. It is precursor of another form of vitamin D, ergocalciferol ( ).
# (d) Coprosterol : It is found in faeces. It is formed as a result of the reduction by bacteria in intestine from the double bond of cholesterol between C5 and C6.
# (e) Tarpens : It is essential oil and present mostly in oils of camphor, eucalyptus, lemon and mint. Phytol is a terpenoid alcohol present in Vitamin A, K, E and in pigments like chlorophyll carotenoid. Other forms are licopene, gibberellins and natural rubber.
# (f) Prostaglandin : It is hormone like compound derived from arachidonic acid. Mostly present in secretion of seminal vesicles in males and menstrual cycle fluid in females.
# (g) Blubber : A very thick layer of subcutaneous fat in whale.
(iv) Functions of lipids
(a) Oxidation of lipids yields comparatively more energy in the cell than protein and carbohydrates. 1gm of lipids account for 39.1 KJ.
(b) The oil seeds such as groundnut, mustard, coconut store fats to provide nourishment to embryo during germination.
(c) They function as structural constituent i.e. all the membrane system of the cell are made up of lipoproteins.
(d) Amphipathic lipids are emulsifier.
(e) It works as heat insulator.
(f) Used in synthesis of hormones.
(g) Fats provide solubility to vitamins A, D, E, and K.
Lipids : Term lipid was coined by Bloor. These are esters of fatty acids and alcohol. They are hydrophobic insoluble in water but soluble in benzene, ether and chloroform. Lipids are classified into three groups:–
lkjhg(i) Simple lipids : These are the esters of fatty acids and glycerol. Again they are typed as :–
# (a) Fats and Oils : (Natural lipids or true fats). These triglycerides of fatty acid and glycerol. Fats which are liquid at room temperature are called oils. Oils with polyunsaturated fatty acids are called polyunsaturated e.g. sunflower oil, lower blood cholesterol.
# (b) Fatty acids : Obtained by hydrolysis of fats. Formic acid is simplest fatty acid (HCOOH). These are of 2 types :–
Saturated fatty acids : The fatty acids which do not have double bond in between carbon atoms.e.g. butyric acid, palmitic acid,hexanoic acid, etc. They have high melting points, solid at room temperature and increase blood cholesterol.
Unsaturated fatty acids : The fatty acids which have double bonds in carbon atoms. e.g. 8 hexadecanoic acid, 9 octadecanoic acid etc. They have lower melting points mostly found in plant fats, liquid at room temperature and lower the blood cholesterol.
# (c) Waxes : These are simple lipids composed of one molecule of long chain fatty acid and long chain monohydric alcohol. Waxes have high melting point, insoluble in water, resistant to atmospheric oxidation, chemically inert and not digested by enzymes. They reduce rate of transpiration by making plant tissue water proof and work as excellent lubricant.
Types of waxes
Plant wax : Forms coating.
Bee's wax : It is secretion of abdominal glands of worker honeybee. It consist of palmitic acid and myricyl alcohol.
Lanolin or Wool fat : It is secreted by cutaneous glands, also obtained from wool of sheeps. It consists of palmitic acid, oleic or stearic acid and cholesterol.
Sebum : It is secretion of sebaceous gland of skin.
Paraffin wax : Obtained from petrolium.
(ii) Compound lipids : They contain some additional or element. Group with fatty acid and alcohol on the basis of group they may be of following types:
# (a) Phospholipids : These contain phosphoric acid. It helps in transport, metabolism, blood clotting and permeability of cell membrane. It is a bipolar molecule i.e. phosphate containing end is hydrophilic whereas fatty acid molecules represent hydrophobic (non-polar tail). Phospholipids again comprises.
- Lecithin : These are yellowish grey solids, soluble in ether and alcohol but insoluble in acetone. On hydrolysis they yield glycerol, fatty acid, phosphoric acid and choline. Lecithins are broken down by enzyme lecithinase to lysolecithin. The enzyme is found in venom of bee and cobra.
- Cephalins : Found in animal tissue and soyabean oil. Cephalin contains choline or serine sometimes and stearic acid, oleic acid, linoelic and arachidonic acid.
# (b) Glycolipids : These contain nitrogen and carbohydrate beside fatty acids. Generally found in white matter of nervous system. e.g. sesocine frenocin.
# (c) Chromolipids : It includes pigmented lipids e.g. carotene.
# (d) Aminolipids : Also known as sulpholipids. It contains sulphur and amino acids with fatty acid and glycerol. Cutin and suberin are also compound lipids resistant to water and also provide mechanical support in plants.
(iii) Derived lipids : These are obtained by hydrolysis of simple and compound lipids. Derived lipids include following components :–
# (a) Sterols : Lipids without straight chains are called sterols. They are composed of fused hydrocarbon rings and a long hydrocarbon side chain. Best known sterol is cholesterol, present in high concentration in nervous tissue and in bile. Cholesterol is also the precursor of hormones like progesterone, testosterone, estradiol and cortisol and vitamin D. Diosgenin is obtained from yam plant (Dioscorea) used in making anti- infertility pills.
# (b) Digitalin : It is prepared from leaves of Foxglove (Digitalis lantana) is a heart stimulant.
# (c) Ergosterol : Present in food, found in ergot and yeast. It is precursor of another form of vitamin D, ergocalciferol ( ).
# (d) Coprosterol : It is found in faeces. It is formed as a result of the reduction by bacteria in intestine from the double bond of cholesterol between C5 and C6.
# (e) Tarpens : It is essential oil and present mostly in oils of camphor, eucalyptus, lemon and mint. Phytol is a terpenoid alcohol present in Vitamin A, K, E and in pigments like chlorophyll carotenoid. Other forms are licopene, gibberellins and natural rubber.
# (f) Prostaglandin : It is hormone like compound derived from arachidonic acid. Mostly present in secretion of seminal vesicles in males and menstrual cycle fluid in females.
# (g) Blubber : A very thick layer of subcutaneous fat in whale.
(iv) Functions of lipids
(a) Oxidation of lipids yields comparatively more energy in the cell than protein and carbohydrates. 1gm of lipids account for 39.1 KJ.
(b) The oil seeds such as groundnut, mustard, coconut store fats to provide nourishment to embryo during germination.
(c) They function as structural constituent i.e. all the membrane system of the cell are made up of lipoproteins.
(d) Amphipathic lipids are emulsifier.
(e) It works as heat insulator.
(f) Used in synthesis of hormones.
(g) Fats provide solubility to vitamins A, D, E, and K.