Lipid is derived from the Greek word lipos meaning fat. All the organic compounds formed by carbon, hydrogen and oxygen are insoluble in water, but soluble in organic solvents like benzene, ether, alcohol, chloroform, hexane, acetone etc. are called lipids. Only 0.5% of the body is made up of lipids. In 1943 German scientist Bloore first used the term lipid.
Properties of lipids
1. Lipids are colorless, tasteless and odorless substances.
2. It is insoluble in water, but soluble in organic solvents (ether, chloroform, benzene, ethyl alcohol, carbontetrachloride, hexane).
3. They act as esters of fatty acids.
4. As molecular weight increases, its melting point increases (it has no specific melting point).
5. On wet analysis, fatty acids and glycerol are obtained.
6. The relative importance of lipids is less than 1 so they float in water. The relative importance of lipids is 0.86.
7. Its nature is either hydrophobic or amphiphilic.
8. They are small and have a molecular weight of less than 10,000 daltons.
9. Lipids that are liquid at normal temperature are called oils and semi-liquid or solid lipids are called fats.
10. It reacts with Sudan-III and acquires a red color. Dr. Abu Bakkar Siddiq
11. It disperses homogeneously in water.
12. Hydrolysis of lipids in the presence of alkali produces soaps.
13. Lipids are liquid and solid at normal temperature.
Source of Lipid
1. Animal Sources: Animal sources of lipids include animal fat, butter, ghee, butter, eggs etc.
2. Plant sources: Soybean, sesame, linseed, sunflower, groundnut, palm, coconut, mustard, reedy, olive etc. are vegetable sources of lipids.
Chemical examination of lipids
1. Lieberman Burchard test: After dissolving the lipid in chloroform and adding a few drops of acetic anhydride and dark H2SO4, it first turns red, then blue and finally bluish-green.Dr. Siddiq Publications
2. Sakowski test: If the lipid is dissolved in chloroform and an equal amount of dark H2SO4 is added, it first turns bluish-red and then turns dark red.Dr. Abu Bakkar Siddiq
Classification of lipids
Lipids are of two types based on their reaction with NaOH/KOH.
1. Saponification: These lipids contain a functional ester group and are hydrolyzed in alkaline media. Such as triglycerides, phospholipids, glycolipids, sphingolipids, waxes etc. Abu Bakr Siddique
2. Non-saponification: These lipids do not contain functional ester groups and are not hydrolyzed in alkaline media. E.g.- terpin, prostaglandin steroid etc.
Lipids are divided into five categories based on molecular structure.
1. Neutral lipids, 2. Phospholipids, 3. Glycolipids, 4. Terpenoids and 5. the wax
Simple Lipid
Those lipids which, when broken down or analyzed, yield no other constituents other than fatty acids and glycerol, are called simple lipids. It is of two types. These are-
1. Triglycerides or Sneha Drovia: Esters of fatty acids and glycerol are called Sneha Drovia. It is composed of three molecules of fatty acid and one molecule of glycerol. Hence it is called triglyceride. Excess triglycerides cause atherosclerosis, a disease that causes heart attacks and strokes. Triglycerides are divided into two parts.
(i) Oils: Triglycerides which are composed of unsaturated fatty acids and are liquid at normal temperature (200C) are called oils. Their melting point is very low, 50C. close to Vegetable fats and palm oil have high melting points. Coconut oil coagulates at low temperatures.
(ii) Fats: Those composed of triglycerides containing saturated fatty acids and solid at normal temperature (20°C) are called fats. Their melting point is high, 70 0C. close to Such as fish oil, butter, ghee, coconut oil, animal fat, olive oil, palm oil and chocolate.
Function: Fruits and seeds of plants contain oils and fats as stored food. During germination, oils and fats are converted into carbohydrates and provide food for the growing embryo.
Functions/importance of oils and fats
(i) Oils and fats are concentrated sources of energy. They act as a source of energy in the absence of sugar supply.
(ii) Fat cells present in adipose tissue prevent heat loss and maintain normal body temperature.
(iii) Vitamins A, D, E and K are fat soluble vitamins. All these vitamin needs are met by consuming oil-like food.
(iv) Oils and fats are the main sources of fatty acids in the body. It has metabolic and structural functions.
(v) The fat stored in the fruits and seeds of plants is stored as food.
(vi) The oils and fats stored in the seeds are converted into sugars and provide nourishment to the growing embryo.
(vii) Fat increases the risk of heart disease by increasing LDL levels in the body.
(viii) The oil reduces the risk of heart disease by reducing the level of LDL in the body.
2. Wax: Ester of fatty acid and monohydric alcohol with high molecular weight is called wax. Carbon numbers of fatty acids are 14-36 and carbon numbers of alcohols are 16-36. Waxes are insoluble in water, but soluble in organic solvents. It is chemically inert. Remains solid at normal temperature. The stems, leaves, flowers and fruits of plants contain wax. Carnoba wax is produced from the Brazilian palm tree. Different types of wax are – lanolin, beeswax, feather wax, hair wax, bewax, carnoba, sebum, cerumen, suberin etc.
Properties of wax
(i) Wax is colorless and odorless.
(ii) Waxes are insoluble in water, but soluble in organic solvents.
(iii) It is chemically inert.
(iv) Wax remains solid at normal temperature.
(v) It contains saturated fatty acids.
(vi) It is water repellent.
(vii) Its melting point is higher than fat.
Functions/importance of wax
(i) Wax acts as a water resistant layer on the stem, leaves, fruits and flowers of plants.
(ii) Wax acts as a preservative in plant organs.
(iii) Candles are made from wax.
(iv) It is used in cosmetic industry.
(v) Waxy feathers and feathers are water resistant.
(vi) Reduces waxy sensation on leaves and young stems.
(vii) Cutin and suberin coat are formed in the cell wall. Cutin and suberin are waxy substances.
(viii) It is used in fruit preservation.
Compound lipids
1. Glycolipid
Lipids that are composed of fatty acids, glycerol and carbohydrates (glucose) are called glycolipids. This is known as glycocalyx. Such as Cerebron, Nervon etc. Dr. Siddiq Publications
Different types of glycolipids are-
(i) Cerebroside: A glycolipid composed of glycerol, fatty acids and glucose or galactose is called cerebroside. It resides in the animal brain.
(ii) Sulphatide: A glycolipid composed of glycerol, fatty acid and sulphate is called sulphide. It is present in kidney, liver, salivary gland, testis, chloroplast etc.
(iii) Gangliosides: Glycolipids composed of glycerol, fatty acids and oligosaccharides are called gangliosides. It is in the animal’s brain, nerve cells, spleen and red blood cells.
Functions of glycolipids
(i) Glycolipids are used as markers in cell interactions.
(ii) It plays a role in the immune response of the body by recognizing the virus.
(iii) It forms the membrane of chloroplast.
(iv) Participates in the process of photosynthesis.
(v) Galactose combines with lipids to form galactolipids.
(vi) Glycolipids form human blood group.
(vii) This lipid is found in cotton and sunflower seeds.
(viii) It forms the myelin sheath of neurons.
2. Phospholipid
Lipids that are composed of fatty acids, glycerol and phosphate are called phospholipids. Its constituents are phosphotidic acid. Lecithin when the phosphate group of phospholipid is esterified with choline and serine when esterified with hydroxyl gives cephalin. Lecithin was the first phospholipid identified. Phospholipid holo-lecithin, cephalin, plasmalogen, choline, serine, cardiolipin, sphingomyolin etc.
Phospholipids are of three types. These are-
(i) Phosphoglycerides: Phospholipids composed of glycerol, fatty acids and phosphoric acid are called phosphoglycerides. It is present in the cell membrane. Such as lecithin. Dr. Siddiq Publications
(ii) Phosphoinositide: Phospholipids composed of glycerol, fatty acids, phosphoric acid and inositol are called phosphoinositides. It is present in the brain. It is found in soybeans.
(iii) Phosphosphingoside: Phospholipids composed of fatty acids, phosphoric acid and sphingosine are called phosphosphingosides. It resides in the nervous system of animals.
Functions of phospholipids
(i) Phospholipid forms the membrane of cell mitochondria, chloroplast, tonoplast, endoplasmic reticulum, nucleus etc.
(ii) It regulates cell permeability and transport processes.
(iii) Acts as a prosthetic group in some enzymes.
(iv) It helps in coagulation or coagulation of blood in the animal body.
(v) It acts as cell ion. Blocks diffusion of glucose, water and charged ions.
(vi) It increases the rate of oxidation.
(vii) It plays an important role in acetylcholine neurotransmission.
(viii) It helps in jasmonic acid production in plant cells. Jasmonic acid participates in disease prevention.
(ix) It maintains the internal stability of the cell.
3. Lipoprotein
Lipids that are composed of fatty acids, glycerol and proteins are called lipoproteins. These lipids are present in the membranes of mitochondria and chloroplasts. It is involved in the electron transport system of mitochondria and generates energy. Lipoproteins are present in plasma, egg yolk and milk. Example- Cutin, Suberin etc.
There are 5 types of lipoproteins. These are-
(i) Chylomicron: Chylomicron is a lipoprotein particle composed of fat and protein. It acts as a carrier of cholesterol.
(ii) VLDL : Very Low Density Lipoprotein is called VLDL. It is very low density lipoprotein.
(iii) IDL : Intermediate Density Lipoprotein is abbreviated as IDL. It is medium density lipoprotein.
(iv) LDL : Low Density Lipoprotein is abbreviated as LDL. It is low density lipoprotein. The normal level of cholesterol in the blood is 0.15-1.20%. High levels of LDL in the blood are harmful (<100 mg/dl). LDL carries about 1500 cholesterol esters per molecule. If the level of cholesterol in the blood is high, it accumulates in the lining of the blood vessels and narrows the blood flow. It increases blood pressure in the body and reduces blood flow. As a result, blood flow to the heart decreases and heart disease occurs. If its level is high, the person becomes unconscious. Chest pain. A heart attack may occur. Heart failure occurs. Coronary thrombosis may occur. Generally men have higher LDL and women have lower. LDL is called bad cholesterol).
(v) HDL : High Density Lipoprotein is abbreviated as HDL. It is high density lipoprotein. It is good to have high levels of HDL in the human blood (40