Q.1. What are lipids? Define.
Ans. The lipids are a heterogeneous group of organic compounds present in plant and animal tissues and related either actually or potentially to the fatty acids and chemically they are various types of esters of different alcohols.
Q.2. What are Bloor’s criteria for a substance to be called a lipids?
Ans. Bloor gave the following criteria for a substance to be called as lipid:
- Insoluble in water
- Soluble in one or more organic solvents such as ether, chloroform, Benzene, acetone etc, so called “fat solvents”.
- Related to fatty acids as ester either actual or potential
- Possibility of utilization by living organisms.
Q.3. What is an oil? How it is related to lipids?
Ans. An oil is a lipid which is liquid at ordinary temperature. Distinction between fats and oil is purely physical one; chemically they are all esters of fatty acids and alcohol.
Q.4. State the biomedical importance of Lipids.
Ans.
- Important dietary constituent and acts as “fuel” in body yielding energy.
- Lipids supply essential fatty acids (EFA) in the diet.
- Some vitamins like A, D, E and K are fat soluble.
- Nervous system is rich in lipids and are essential for proper functioning.
- Breakdown products of fats like acetyl CoA can be used by the body for synthesis of cholesterol, steroid hormones, etc.
- Lipoproteins and phospholipids (PL) are important constituents of many natural membranes such as cell walls and cell organelles like mitochondria, etc.
- Some lipid deposits exert an insulating effect, while lipids deposited around internal organs have protective function.
- Lipoproteins are “carriers” of trigylcerides (TG), phospholipids (PL) and cholesterol in the blood.
- Phosphatides of platelets, called platelet factor 3 are involved in the production of thromboplastin activity in the early stages of blood coagulation.
- Dipalmitoyl lecithin (DPL), a derivative of lecithin (PL) acts as a surfactant and lowers the surface tension in the lung alveoli.
Q.5. How are lipids classified? Give examples of each group.
Ans. Bloor has classified lipids as:
Simple lipids: Esters of FA with various alcohols.
Examples:
- Neutral fats (triacyl glycerol) are esters of fatty acids with glycerol.
- Waxes: Esters of fatty acids with monohydroxy aliphatic alcohols other than glycerol.
Compound lipids: Esters of fatty acids containing groups other than and in addition to an alcohol and fatty acids.
They are of various types as follows:
- Phospholipids (PL): Consists of fatty acids + glycerol + phosphoric acid + a nitrogenous base or other constituents.
Examples:
- Phosphatidyl choline (lecithin),
- Phosphatidyl ethanolamine (cephalin),
- Sphingomyelin etc.
- Glycolipids: Consists of sphingosine (alcohol) + fatty acids + carbohydrate + carbohydrate derivative. They do not contain glycerol or phosphoric acid.
Examples:
- cerebrosides
- gangliosides
- Sulfolipids: Lipids containing sulphate groups
- Aminolipids (proteolipids)
- Lipoproteins: Lipids as a prosthetic group to proteins called apo-proteins + PL + cholesterol/and cholesteryl esters.
Derived lipids: Substances derived from above groups by hydrolysis e.g. fatty acids, glycerol and other alcohols, cholesterol.
Miscellaneous: Aliphatic hydrocarbons, carotenoids, squalene, vit E, vit K, etc.
Q.6. What is a fatty acid? Define.
Ans. A fatty acid (FA) may be defined as an organic acid that occurs in a natural triglyceride and is a monocarboxylic acid ranging in chain length from C4 to about C24.
Q.7. What are saturated fatty acids? Give examples.
Ans.
- Fatty acids which do not have any double bond in their structure are called saturated fatty acids.
Examples: Acetic acid (CH3.COOH), propionic acid (C2H5COOH), butyric acid (C3H7COOH), etc. Higher homologues like palmitic acid (C15H31COOH), stearic acid (C17H35COOH), etc.
Q.8. What are unsaturated fatty acids? What are the types?
Ans.
Fatty acids which contain double bonds in their structure are called unsaturated fatty acids (UFA).
- Types: Depending on the degree of unsaturation they are divided into two groups:
- Monounsaturated (mono-ethenoid): containing only one double bond.
- Polyunsaturated (polyethenoids): containing more than one double bond in their structure.
Q.9. Give an example of monosaturated FA (monoethenoid) found in our body fat.
Ans. Oleic acid C17H33COOH (Formula 18: 1; 9) is found in abundance in our body fat.
Q.10. Name the three polyunsaturated fatty acids (polyethenoids).
Ans. Three polyunsaturated fatty acids of biological importance are:
- Linoleic acid: Two double bonds between C9 and C10 and another between C12 and C13 (Formula: 18: 2; 9, 12).
- Linolenic acid: Contains Three double bonds between carbons 9 and 10, 12 and 13, and 15 and 16. (Formula: 18: 3; 9, 12, 15).
- Arachidonic acid: It is a 20 C fatty acid and contains Four double bonds between 5 and 6, 8 and 9, 11 and 12, and 14 and 15. (Formula: 20: 4; 5, 8, 11, 14).
Q.11. Name two cyclic fatty acids of clinical importance.
Ans.
- Chaulmoogric acid and
- Hydnocarpie acid
Both of them were used earlier for a long time for treatment of leprosy.
Q.12. Name essential fatty acids (EFA). Why are they called essential?
Ans. Three polyunsaturated fatty acids:
- Linoleic acid
- Linolenic acid and
- Arachidonic acid are called essential fatty acids (EFA).
They are called essential as they are necessary for normal growth and body functions. They cannot be synthesized in the body and must be provided in the diet.
Q.13. Which EFA is important?
Ans.
- Linoleic acid is most important as arachidonic acid can be formed in the body from linoleic acid.
- Biologically arachidonic acid is very important as prostaglandins (PGs) and leukotrienes (LTs) are formed in the body from it.
Q.14. Monounsaturated fatty acid oleic acid is found in plenty in the body, then why EFA cannot be synthesized in the body from oleic acid?
Ans. Introduction of additional double bonds (called desaturation) in an unsaturated FA can take place between COOH group and existing double bond but it cannot do so between existing double bond and CH3 group (omega carbon). This explains why body cannot synthesize EFA from oleic acid.
Q.15. State the deficiency manifestations of EFA.
Ans. EFA deficiency causes:
- Cessation of growth
- Skin lesions (Dermatitis)
- Kidney damage
- Abnormalities in pregnancy and lactation in adult females
- Fatty liver and
- Decreased resistance to stress.
Q.16. Enumerate the important functions of EFA.
Ans.
- Are structural elements of various tissues.
- Lipids of gonads are rich in EFA and are involved in reproductive function.
- Prostaglandins (PGs) and leukotrienes (LTs) are synthesized from arachidonic acid.
- Lowers cholesterol level in blood.
- Prolongation of clotting time.
- Increase in fibrinolytic activity.
- EFA deficiency produces fatty liver.
- Linoleic acid is necessary for synsthesis of Docosahexenoic acid present in retinal photoreceptor membrane.
Q.17. What is glycerol?
Ans. Glycerol is commonly called as glycerine. Chemically it is a trihydric alcohol containing three -OH groups in the molecule.
Q.18. What are the sources of glycerol in the body?
Ans. Sources of glycerol in the body:
- Exogenous: From dietary fats, approximately 22% of glycerol formed in the gut by lipolysis of dietary TG is absorbed directly to portal blood.
- Endogenous: From lipolysis of fats (TG) in adipose tissue.
Q.19. What is acrolein test?
Ans. The presence of glycerol in a compound is detected by acrolein test. Glycerol, when heated with KHSO4, two molecules of water are removed and it produces acryl aldehyde which has characteristic pungent or acrid odour.
Q.20. Is glycerol produced in the body by lipolysis a waste product or useful?
Ans. Glycerol produced in the body is not a wasteproduct. It is useful in that:
- Re-esterified to form TG again
- It has nutritive value. It can be converted to glucose/and glycogen by the process called gluconeogenesis.