LIPIDS or FATS

Lipids are the group of fats and fat like substances. They are the compounds of carbon, hydrogen and oxygen but they differ from carbohydrates in that the hydrogen and oxygen are not in the same proportions as in water. They are insoluble in water but soluble in organic solvents like acetone, ether, alcohol, etc.They needs a large amount of oxygen for their oxidation to release energy. True lipids are esters of fatty acids and an alcohol.

Sources of fats – the principal sources of fats in our diet are cooking oil, butter, ghee, oil seeds, milk, mutton, cheese, eggs, etc.

Classification of lipids – lipids are grouped into three categories:

(a) Simple lipids

(b) Complex lipids

(c) Derived lipids

(a) Simple lipids – these are various types of fats, oils or waxes.

(i) Fats: These are esters of fatty acids and glycerols. These are also called as triglycerides. Each molecule of glycerol can react with three molecules of fatty acids. Depending upon number of fatty acids attached they are called mono, di or triglycerides.

·         Monoglyceride- one molecule of glycerol + one molecule of fatty acid.

·         Diglyceride- one molecule of glycerol + two molecules of fatty acids.

·         Triglycerides- one molecule of glycerol + three molecules of fatty acids.

(ii)Oils: These are fats, which are rich in unsaturated fatty acids (fatty acids with more than one double bond)

Importance of oils – Because of the presence of unsaturated fatty acids they are recommended to people who are suffer from high blood cholesterol of cardio- vascular diseases, they tend to lower the high blood cholesterol without raising the fat. The cholesterol leads to thickening of arteries, which became a cause of high blood pressure.

(iii) Waxes – These are esters of long chains fatty acids and long chains alcohol other than glycerol. They are mainly protective in functions and form water soluble coating on hair and skin in animals and on stems, leaves and fruits of plants.

(b) Complex lipids – These lipids are complex as they are formed in association of either of carbohydrates or phosphates or proteins.

(i) Glycolipids – These are formed by association of lipids with carbohydrate molecules. These are found in membranes.

(Glycolipids = lipids +carbohydrate)

(ii) phospholipids- These are lipids containing a phosphate group.(phospholipids= lipids + phosphate)

(iii) Lipoprotein – These are lipids associated with proteins molecules.(lipoproteins = lipids + proteins molecules)

c. Derived lipids – These include hydrolyzed products of simple and complex lipids.e.g. – Steroids (cholesterol).

Steroids - Steroids are composed of fused hydro- carbon rings and a long hydrocarbon chain.e.g. Cholesterol, Diosgenin.

 Importance of cholesterol - It is a steroid lipid. It is said to create abnormal thickening of walls of arteries. It can raise blood pressure and hence may lead to circulatory problems. It is said that is not bad but not useful as well.

Importance of steroids –

(i) Cholesterol is a precursor molecule of many sex hormones like progesterone, testosterone and adrenocortico- tropic hormones.

(ii) Cholesterol on irradiation by ultraviolet rays forms vitamin D necessary for growth of bones.

(iii) Diosgenin is used in the manufacture of anti- fertility pills.

Function of lipids

·         Lipids as rich source of energy – Lipids provide the energy fuel. The caloric value of 1gm of fats is 9.45 k cal while the physiological fuel value of 1 gm of fats is 9.0 k cal.

·         As heat insulator – Fats are deposited in the subcutaneous tissues. These acts as insulator.

·         As food reserve – Triglycerides stored in adipose tissue as principal food reserve.

·         As solvent – Lipids acts as a solvent for fat- soluble vitamins like- A, D, E and k.

·         Acts as cushions – They absorb mechanical impact around organs like eyeball.

·         Phospholipids- They form constituents of membranes of various organs.

·         Glycolipids- They form components of cell membranes and myelin of nerve cells.

       

PROTIENS

Proteins are made up of large number of amino acids linked together chemically.

Proteins are most complex chemical compounds formed of C, H, O,N, S, P. The characteristic element is the nitrogen . All the reactions in the body are controlled by proteins, known as enzymes.

Proteins are made up of some 20 different naturally occurring amino acids linked together chemically. They are polymers made up of chains of amino acids. These amino acids are linked by peptide bond or peptide linkage. During digestion, these proteins are broken down into amino acids and absorbed through the intestinal wall.

Sources of Proteins- Principal sources of  proteins are pules, meat, fishes,eggs, milk soya bean, cereals, etc.

Daily Requirements- An adults person needs on an average about 70-100gm of proteins per day. The growing children and protein. Approximately 15% of proteins should be present in human diet.

Categories of proteins: On basis of chemical nature, proteins are divided into three categories -

(a) Simple proteins - These are formed of peptide chains ans yield only amino acids on hydrolysis. examples are albumin, globulin, histones, protamines, etc.

(b) Conjugated proteins - These are the proteins formed in combination with glucose (glycoproteins), lipid(lipoproteins), phosphate (phosphoprotein0, etc. examples are casein, blood antigens, haemoglobin of RBCs, etc

(c) Derived proteins -  These are the protiens which are formedby partial hydrolysis of simple proteins. examples are peptones, proteoses, etc.

AMINO ACIDS-  Proteins are the polymers made up of chains of amino acids. Thus amino acids are building blocks of protiens. many amino acids are linked one another to form protein. hence, amino acids are called monomers of proteins. It consists following characteristics:

1. These are the basic units of protiens.
2. All amino acids have at least one acidic caboxylic group (- COOH) and one basic amino group(-NH2).
3. These are colorless, crystalline solids.
4. These are soluble in water and insoluble in organic solvents.

Examples of amino acids are alanine, glycine, serine, leucine, isoleucine, etc. the simplest amino acid is glycine.

Formation of peptide bond: A peptide bond is formed when two amino acids are joined together by a peptide bond. A polypeptide is formed when numbers of successive amino acids are joined together in a long chain of peptide bond.

Categories of amino acids : There are 20 types of amino acids. on tha basis of nutritional value, they are divided into two categories.

(i) Essential amino acids : These are the amino acids which are not synthesized in the body. therefore, they must be included in diet. These are leucine, isoleucine, lysine, phenylalenine, trytophan, valine, methionine, and threonine. These are eight in number.

(ii) Non essential amino acids - These are the amino acids which are synthesized in the body. they may or may not be present in the diet. These are alanine, serine,glycine, glutamine, tyrosine, asparatic acid, cysteine, arginine, histidine, proline, glutamic acid and asparagine.

Functions of protein: Proteins as building blocks- Many proteins act as structural proteins ans take part in building and repairing of the body tissues. Therefore, these are essential for the growth.

1. Proteins as energy - Proteins provide energy fuel. The caloric value of 1 gm of protein is 5.654 kcal while the physiological fuel value of 1gm of proteins is 4.0 kcal.
2. Proteins as enzymes - These act as enzymes or bio-catalyst which regulate life processes. Nearly 2000 different kinds of enzymes are known as far.
3. Protein as hormones - Some hormones are  proteins, such as insulin (a hormone regulating glucose balance).
4. Protein as defensive - Some proteins are antibodies or immunoglobins. They neutralize the foreign bodies and develop immunity.

     5.  Thrombin and fibrirogen cause blood clotting.

Diseases due to protein deficiency - The proteins are essentials for the body growth. their deficiency in the diet causes retardation of physical growth and mental growth. Deficiency of proteins causes two diseases in infants; marasmus and kwashiorker.                                                                             

CARBOHYDRATES

           There are mainly compounds of carbon, hydrogen and oxygen. Hdrogen and oxygen are generally occuring in the ratio of 2:2, thus known as hydrates of carbon (CH2O). The general formula of carbohydrates can be written as Cn(H2O)n.

Sources of Carbohydrates: Carbohydrates are found in wide variety in wide variety of foods. Its important sources are cereals (wheat, maize, rice), potatoes, sugarcane, fruits, breads, milk, etc.
Daily Requirement- A healthy adult person requires on average 500g carbohydrates per day. Approximately 55-75% of total  food calories should be taken in form of carbohydrates. Carbohydrates requirements may be more for athletes, mountaineers, labourers, etc.
Categories of Carbohydrates- Carbohydrates are classified according  to the complexity of chemical substances of which they are formed. They are grouped into:
              (a) Monosacccharides
              (b) Disaccharides
              (c) Polysachharides 
(a) Monosaccharides
(i)  These are chemically simplest forms of carbohydrates in which carbohydrates can exists.
(ii) They cannot be hydrolyzed into smaller carbohydrates.
(iii) Common examples are glucose, fructose, and galactose.
(iv) They are simple sugars, composed of 3-7 carbon atoms
(v)  They are classified according to number of carbon atoms.

NUTRITION

         The sum total processes of taking in, digestion, absorption, and assimilation of food are known as nutrition. It is important because-
(i)   it provides energy to the body to perform various activities,
(ii)  it provides essential materials for growth,
(iii) it maintains the body temperature.

Types of Nutrition
There are two main types of nutrition:
(a)Autotrophic or holophytic nutrition: It is the process by which organisms can synthesize their food by process of photosynthesis. It is found in green plants. The green plants possess chlorophyll pigment. It helps plants to trap solar energy and manufacture the food (in form of simple sugar) by utilizing simple inorganic materials of nature . Such organisms are known as autotrophs.

(b)Heterotrophic nutrition: It is the process by which organisms cannot synthesis their food by themselves. They are dependent on autotrophs directly or indirectly. They are found in all animals and non-green plants like fungi and bacteria.Such organisms are known as heterotrophs . Depending upon the mode of feeding, there are three types of heterotrophic nutrition:
(i)   Holozoic nutrition- organisms like man depend  on solid food materials.
(ii)  Saprozoic nutrition- organisms like fungi, some bacteria, etc. 
(iii) Parasitic nutrition- organisms like Ascaris, tapeworm, etc. depend either or completely on their hosts. They are called parasites.

Nutritional Requirements 
Before discussing the digestive system, it is necessary to have an understanding of the body  regarding nutrition i.e. the dietary constituents and their functions within the body.

Food and Nutrients- Food can be defined as any essential substance that when absorbed into the body tissues, yields material for the production of energy, growth and repair of tissues and regulation of life processes.


Functions of  food

• acts as a fuel to provide energy,
• promotes body function,
• provides essential materials for growth and reproduction,
• helps in repair of body tissues,and 
• develops immunity against diseases.

Components of food
The food of an animal consists of mainly six types of food components-

(1) Carbohydrate    (2) Proteins

(3) Fat                     (4) Vitamins

(5) Minerals           (6) Water