Calorific value of proteins carbohydrates and fats Neet

 Carbohydrates (Polyhydroxy aldehydes (or) ketones.) 

A carbohydrate is composed of carbon, hydrogen and oxygen in the the ratio of 1:2:1 (CH2 O)n. They are of three types namely monosaccharides, disaccharides and polysaccharides 

Monosaccharides:

• 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 (C3 H6 O3 ) are common intermediary products in carbohydrate metabolic processes. They play an important role in inter con version of biomolecules. (eg. glyceraldehydes). 
• Pentoses (C5 H10O5 ) like ribose and deoxyribose are the integral components of RNA and DNA molecules. 
• The Hexoses(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 yielding energy equivalent of 4.1 calories.

Disaccharides 

• These are the carbohydrates formed by the condensation of two monosaccharide monomers. These are found in common food substances such as milk and sugar. 
• There are three common disaccharides namely maltose, sucrose and lactose. 

They have the following composition

Maltose(In germinating cereals)  ----> glucose + glucose 

Sucrose (cane sugar) ---->glucose + fructose 

Lactose (milk) ----> glucose + galactose

Polysaccharides

• These are complex carbohydrates formed by the 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 trapping enormous amounts of energy. In food grains, starch is available as pectin and amylopectin molecules. 
• Glycogen, a polysaccharide is found in the liver and muscles.

Proteins(Polypeptides) 

• 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 functional proteins. 
• The building blocks of proteins are amino acids. There are approximately twenty different types of amino acids, such as glycine, alanine, serine, valine, leucine, proline etc. 
• The amino acids are classified as essential and non-essential amino acids. Essential amino acids can not be synthesised in our bodies. 
• Hence they should be made available through food. The essential amino acids are arginine, valine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine and tryptophan. The non-essential amino acids can be synthesized in our bodies from other compounds. 
• Such amino acids need not be added to the diet.
• A protein (or) a polypeptide chain is formed of several amino acids linked with each other by peptide bonds. 
• This linear arrangement is termed the primary organisation of a protein. However, in most of the proteins, the 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 organisation are determined genetically. Hence the genome gets its importance due to its capability to produce, specific types of protein for bringing out genetic 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 malnutrition, such as marasmus and kwashiorkor. 
• In marasmus, 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 kwashiorkor, there is a wastage of muscles. Face and feet will have oedema. The belly region will appear enlarged.

Lipids

• 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 a limited amount of fat beneath the skin adds to the 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 the 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 polyunsaturated fatty acids(PUFA) are favoured for persons having high blood pressure and other related ailments. 
• These fatty acids are abundant 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

• Vitamins are complex organic compounds, whose presence in trace amounts 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 as A, 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 lose them easily. 
• Vitamin A, D, E and K, if consumed beyond the 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 a co-enzyme in tissue metabolism and it is found useful in the process of oxidation of glucose in the 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.

Minerals 

• Along with complex organic substances, such as carbohydrates proteins and lipids, our body needs substances such as minerals, vitamins and water as accessory food factors. 
• Of the minerals, certain elements are found in greater concentration. 
• They are sodium, calcium, potassium, magnesium, phosphorus, sulphur and chlorine. 
• Certain other minerals are required in slightly lower concentrations for performing useful functions.
•  These include iron, copper, zinc, cobalt, manganese, iodine and fluorine(trace elements). 
• Of these minerals, a larger portion of certain minerals are concerned with bodybuilding activities such as the formation of bones and teeth (Calcium, Magnesium and Phosphorus).
•  Trace elements and other minerals are useful in physiological activities such as oxygen transport (Iron), hormone synthesis (Iodine) and intermediary metabolism (Manganese, Copper, Zinc). 
• Some of the elements remain as constituents of the body fluids (Chlorine, Sodium and Potassium). 
• The presence of certain minerals is essential for neuro-muscular irritability (Magnesium, Sodium and Potassium), blood clotting (Calcium), cardiac functions (Potassium and Calcium).