Unit 1: Carbohydrate

Here is the transcribed text from the image: Unit-1, Part-3 (Carbohydrates) Unit-1, Part-3 Definition: Carbohydrates are hydrates of carbon. Carbohydrates are polyhydroxy aldehydes or ketones or substances that yield one of these compounds on hydrolysis. Chemical Composition: Carbon, Hydrogen & Oxygen. Empirical Formula: n=3 or more. Example: Glucose - ​ But exception is deoxyribose sugar of DNA whose molecular formula is ​ (Ribose) which is present in RNA. Classification of Carbohydrates: The main classification of carbohydrates is done on the basis of hydrolysis. These are (i) Monosaccharides (ii) Disaccharides (iii) Oligosaccharides (iv) Polysaccharides (i) Monosaccharides Monosaccharides are single sugar units that can’t be hydrolyzed into smaller units under reasonably mild conditions. They have the general formula Monosaccharides may be Aldoses, if they contain aldehyde group ( Ketoses, if they contain ketone group ( Again depending upon the number of carbon atoms, monosaccharides may be trioses, tetroses, pentoses, hexoses and heptoses. Some common examples of monosaccharides are Glucose, Ribose. Functions of Monosaccharides: One major function of a monosaccharide is its use for energy within a living organism. Glucose is a commonly known monosaccharide that metabolizes within the cells to yield energy. In the presence of oxygen, glucose breaks down into carbon dioxide, water, and energy is released as a byproduct. Monosaccharides are the building block materials for all complex carbohydrates like starch, glycogen, etc. The sweetness of ripened fruits is due to the presence of monosaccharides like fructose, sucrose, etc. Among them, D-fructose has the highest sweetness. Monosaccharides also exhibit optical isomerism. The naturally occurring sugars are generally in D-form. Most of the monosaccharides, except a few ketones, exhibit mutarotation. Monosaccharides form a variety of derivatives which are constituents of structural and storage polysaccharides. Ascorbic acid (Vitamin C) is an important sugar acid of great biological importance. Sugar acids are produced by the oxidation of the aldehyde group or primary alcohol group of both D-monosaccharides. Reducing property of the reducing sugars like glucose and fructose, etc. help in the analysis of blood and urine for the diagnosis of diabetes, estimation of sugars in the plant samples, etc. Monosaccharides are soluble in water. Disaccharides: Also called a double sugar or bi-ose. Disaccharides are those sugars formed between when two monosaccharides are joined by glycosidic linkage or bond. Like monosaccharides, disaccharides are soluble in water. The joining of simple sugars into a double sugar happens by a condensation reaction, which involves the elimination of a water molecule from the functional group only. The most common examples of disaccharides are sucrose, lactose, and maltose. Oligosaccharides: Oligosaccharides contain two to ten units of simple sugars, joined by glycosidic linkage or bonds. There are few trisaccharides occurring naturally, for example, raffinose, found in many plants. Other oligosaccharides are generally not found as naturally occurring sugars. However, they are produced as hydrolysis products of polysaccharides. Example: (List of examples is cut off in the image) Role of Oligo & Disaccharides: Oligosaccharides containing 2-10 units of simple sugar units joined by glycosidic bonds are having much biological and commercial importance. Sucrose, a disaccharide, is the sugar of commerce. It is abundantly present in ripened fruits like mango, grape, beetroot, sweet potato, etc. Some oligosaccharides exhibit reducing property, e.g., lactose, maltose, cellobiose, etc. However, sucrose and trehalose are non-reducing sugars. Some oligosaccharides exhibit mutarotation, e.g., lactose, maltose, etc., while others do not, e.g., sucrose. Sucrose is the main sugar abundantly present in sprouting shoots and honey. Different soluble disaccharides like sucrose enhance the osmotic pressure of the cell sap and make the cells turgid. Sucrose is also a constituent of nectar of flowers and also the raw material for honey. Lactose, a disaccharide of mammalian origin, is a product of milk secreting glands. Polysaccharides: Polysaccharides may be defined as the polymeric anhydrides of simple sugars. Polysaccharides are carbohydrates that contain more than ten monosaccharide units, generally in terms of hundreds. All polysaccharides can be hydrolyzed with acids or enzymes to yield monosaccharide units and/or monosaccharide derivatives. It may be two types: Homopolysaccharides: Composed of only one type of monosaccharides. Ex: Starch, insulin, cellulose, glycogen, etc. Heteropolysaccharides: Composed of different types of monosaccharides. Ex: Hyaluronic acid of connective tissue, chondroitin, vegetable gum, agar-agar, and heparin, etc. Again, polysaccharides may be: Storage polysaccharides (nutrient or digestible polysaccharides): Starch, glycogen, insulin, etc., are storage polysaccharides. These act as metabolic reserves in plants and animals. Structural polysaccharides: These serve as rigid mechanical structures in plants and animals. Ex: Cellulose, pectin, chitin, chondroitin, hyaluronic acid, etc. Role of polysaccharides: In nature, polysaccharides are the stored form of energy. Nutrient or digestible polysaccharides like starch, glycogen, act as metabolic reserves of monosaccharides in plants and animals. The structural or indigestible polysaccharides like cellulose, pectin, etc. serve as rigid mechanical structures in plants and animals. Starch and glycogen are highly compact polymers that are used for energy storage. Cellulose is used in the manufacture of paper. For the paper industry, cellulose is obtained from bamboos, specific grasses, etc. Chitin, a structural polysaccharide, gives mechanical strength to the exoskeleton of insects and fungal cell walls. The complex polysaccharides like glycoproteins (bounded to proteins), glycolipids (bounded to lipids) are also biologically very important. Polysaccharide is an important component of bacterial capsules