The survival of all living organisms is due to several types of nutritive processes. The process of nutrition involves ingestion digestion, absorption and assimilation of food materials. The composition of nutrients vary in different types of feeding. However, for all living organisms, the nutrient comprises the following organic and inorganic components. They are carbohydrates, proteins, lipids, vitamins, minerals and water. Each component has a specific functional role. A well proportioned intake of nu-trients depends on several factors such as stage of growth, sex, health con-dition, bodily activities and environmental situations.
A carbohydrate is composed of carbon, hydrogen and oxygen in the ratio of 1:2:1 (CH2O)n. They are of three types namely monosaccharides, disaccharides and polysaccharides
These are the simplest form of carbohydrates being comprised of a single organic molecule. Depending on the number of carbon atoms they are classified into trioses, tetroses, pentoses, and hexoses.
The trioses (C3H6O3) are common intermediary products in carbohydrate metabolic processes. They play an important role in inter con version of biomolecules. (eg. glyceraldehydes). Pentoses (C5H10O5) like ribose and deoxyribose are the integral components of RNA and DNA molecules. TheHexoses(C6 H12O6) such as glucose, fructose and galactose are food components commonly consumed.
Carbohydrates are commonly employed by the cells for providing energy. The energy metabolism happens through glycolytic processes involving oxidative, citric acid cycle. The energy liberated is stored in the form of ATPs (Adenosine triphosphate).
Each gram of carbohydrate is capable of yeilding energy equivalent of 4.1 calories.
These are the carbohydrates formed by condensation of two monosaccharide monomers. These are found in common food substances such as milk and sugar. There are three common disaccharides namely mal-tose, sucrose and lactose. They have the following composition
Maltose � glucose + glucose
(In germinating cereals)
Sucrose (cane sugar) � glucose + fructose
Lactose (milk) � glucose + galactose
These are complex carbohydrates formed by polymerisation of a large number of monosaccharides. Nature abundantly produces various types of polysaccharides. Several of them are structural components in the living world eg. chitin, cellulose. Starch molecules serve as storage food materials trap-ping enormous amount of energy. In food grains, starch is available as pectin and amylopectin molecules. Glycogen, a polysaccharide is found in liver and muscles.
Proteins are nitrogenous compounds being made up of carbon, hydrogen, oxygen and nitrogen. Proteins also contain sulphur. In living systems proteins play an important role in the structural organisation eg., cell membrane, hairs, nails and muscles. Many of the proteins serve as enzymes. They are named as functional proteins.
The building blocks of proteins are aminoacids. There are approximately twenty different types of amino acids, such as glycine, alanine, serine, valine, leucin, proline etc. The amino acids are classified as essential and non essential amino acids. Essential amino acids can not be synthesised in our body. Hence they should be made available through food. The essential amino acids are arginine, valine, histidine, isoleucine, leucine, lycine, methionine, phenylalanine, threonine and tryptophan. The non-essential amino acids can be synthesized in our body from other compounds. Such amino acids need not be added in the diet.
A protein (or) a polypetide chain is formed of several amino acids linked with each other by peptide bonds. This linear arrangement is termed as primary organisation of a protein. However in most of the proteins, the straight chain structure gets complicated, into secondary, tertiary or quaternary stages. These levels are due to several other chemical bonds. The complicated nature of a particular protein is specifically required for its prescribed function. The amino-acids sequence and level of ogranisation is determined genetically. Hence the genome gets its importance due to its capability to produce, specific types of protein for bringing out genetical characteristics.
The daily requirement of protein, according to the Nutrition experts committee of ICMR (Indian Council for Medical Research) and WHO (World Health Organisation) is 1 gm per kg body weight. Reduction in the intake of protein leads to protein malnutritions, such as marasmus and kwashiorkar. In marasmas the child loses weight and it also causes severe diarrhoea and the body muscles get wasted. It will appear as though the bones are covered by the skin. In kwashiorkar there is a wastage of muscles. Face and feet will have oedema. The belly region will appear enlarged.
Lipids are important cellular constituents. They are energy rich compounds. They form the most important storage food in the body. In our body, it serves as an insulating material. Cosmetically, the presence of limited amount of fat beneath the skin adds to beauty. Further, steroidal hormones are produced from certain lipids.
The most common type of lipids are the simple lipids (or) triglycerides. They are naturally occurring substances (vegetable oils). In animals it is a main constituent of adipose tissue. Chemically a triglyceride is formed of glycerol and fatty acids.
Fatty acids are of two types namely saturated and unsaturated fatty acids. The unsaturated fatty acids are capable of easier oxidative breakdown, hence poly unsaturated fatty acids(PUFA) are favoured for persons having high blood pressure and other related ailments. These fatty acids are abundent in sunflower oil and safflower oil.
Each gram of lipid is capable of yielding 9.3 calories of energy. It is suggested that 25% to 30% of total calories should come from fat.
Vitamins are complex organic compounds, whose presence in trace amount in the food is essential for growth and other physiological activities. Vitamins do not have any energy value. However they are essential for controlling energy yielding processes. The identified vitamins are classified asA,B,C,D,E and K. Of these, vitamin B and C are water soluble in nature. Vegetables and fruits containing these vitamins if washed in water as cut pieces would loose them easily. Vitamin A,D,E and K, if consumed beyond required level may cause defects, commonly referred to as vitaminosis.
Of the various vitamins, vitamin D or calciferol on exposure to sunlight can be synthesised by our body through the lipid compound called ergosterol, found below our skin. Hence it is known as 'sunshine vitamin'.
The most important functions of vitamins include.
1. Physiological processes : Vitamin A plays a very important role in visual perception. Vitamin E might ensure fertility in animals. The clotting of blood is aided by vitamin K. Vitamin C provides immunity against infections and it may also support processes of growth.
2. Maintenance of body tissues : The epithelial tissues of the body are maintained by vitamin A and B2. The growth of bones is ensured by vitamin D. Vitamin E plays a role in the rejuvenation of tissues. Nourishment to nerve cells is provided by vitamin B1. The process of maturation of erythrocytes is due to vitamin B12.
3. Metabolic processes : The process of calcium and phosphorus metabolism happens due to the presence of vitamin D. Vitamin E remains an antioxidant. Vitamin B1 remains as a co-enzyme in tissue metabolism and it is found useful in the process of oxidation of glucose in CNS. Vitamin B2 is essential for carbohydrate metabolism. Niacin (vitamin B) plays a role as a co-enzyme and is essential for oxidation-reduction reactions. Normal metabolism of amino acids and fat are due to vitamin B6. Biotin (vitamin B) serves as a co-enzyme and co-factor in oxidative metabolism. Vitamin C activates certain intra-cellular enzymes.
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