Introduction, Classification, Chemical Nature and Biological Role of Carbohydrate, Lipids : Pharmaguideline

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Introduction, Classification, Chemical Nature and Biological Role of Carbohydrate, Lipids

Carbonyl compounds found in carbohydrates consist of aldehydes or ketones as well as several hydroxyl groups.



Carbonyl compounds found in carbohydrates consist of aldehydes or ketones as well as several hydroxyl groups. Such compounds may also be produced by derivatives of these compounds upon hydrolysis. Natural organic molecules are known as "saccharides" and are the most abundant types in nature. Simple carbohydrates are those that are soluble in water, sweet in flavor, and are soluble in water.


Sugars can be divided into simple (monosaccharides) and complex (polymer, oligosaccharide, and polysaccharide) carbohydrates.


  • Simple sugar is a carbohydrate that cannot be further hydrolyzed and is often called simple sugar.
  • Solids that are colorless and crystalline, soluble in water but insoluble in non-polar solvents.
  • Aldehydes and ketones are compounds that possess a free aldehyde group.
  • Cn(H2O)n or CnH2nOn is the general formula.
  • Besides being classified according to the amount of carbon they contain, they can also be classified based on the functional groups present.
  • Trioses, tetroses, pentoses, hexoses, heptoses, and also aldoses or ketoses, are dimeric monosaccharides with 3,4,5,6,7,... carbon atoms.
  • Examples – fructose, ribulose, glucose, erythrose.


  • When hydrolyzed, oligosaccharides give off two to ten molecules of monosaccharides.
  • The monosaccharides are linked by glycosidic bonds.
  • In addition to monosaccharides, they can also be classified as disaccharides, trisaccharides, tetra-saccharides, etc.
  • On hydrolysis, an oligosaccharide with two monosaccharides is called a disaccharide, while those with three or four monosaccharides are known as trisaccharides or tetra-saccharides.
  • Cn(H2O)n-1 is the general formula of disaccharides, and Cn(H2O)n-2 is the formula of a trisaccharide.
  • The following disaccharides are examples: sucrose, lactose, maltose, etc.
  • Raffinose and Rabinos are trisaccharide.


  • The term "glycan" is also used for them.
  • They can have hundreds of sugar units in length, with more than ten monosaccharide units in each.
  • The hydrolysis of these polysaccharides yields more than ten monosaccharides.
  • A polysaccharide differs from another in the recurring monosaccharide units they contain, in the chains they contain, in the types of bonds linking these chains, and in the degree of branching they contain.
  • The two most important functions of these cells are structural function and energy storage.
  • Depending on the molecules produced during hydrolysis, they may be further classified.
  • These substances are homopolysaccharides, making up monosaccharides of the same type, or they may contain heteropolysaccharides, that is, monosaccharides of different types.
  • Starch, glycogen, cellulose, pectin, and cellulose are homopolysaccharides.
  • In addition to Hyaluronic acid, Chondroitin is a heteropolysaccharide.

Chemical nature

In addition to carbon and hydrogen, carbohydrates contain oxygen. In general, the structures of carbohydrate molecules are (CH2O)n. Organic compounds containing hydroxyl groups are attached to carbon chains that are organized as aldehydes or ketones. All carbohydrates are made up of monosaccharides, or simple sugars. Polyhydroxy aldehydes (aldose) and polyhydroxy ketones (ketose) are both monosaccharides.

There are three structural forms of carbohydrates:
  1. Carbohydrates with long straight chains have an open-chain structure.
  2. A ring structure is created by linking the -OH groups of the first and fifth carbons of glucose.
  3. Structure Haworth - A structure made up of pyranose rings.
Osazone formation - Sugars react with excess phenylhydrazine to produce osazone, a carbohydrate derivative.

Benedict's test - During heating, reducing sugars turn into powerful reducing substances known as enediols. In a heated solution of Benedict's reagent solution and reducing sugars, the color of the solution changes from orange-red/ brick red to orange-red/ brick red.

Oxidation - The carbonyl groups of monosaccharides oxidize to form carboxylic acids when they are reduced. The oxidation of glucose to D-gluconic acid in Benedict's test makes glucose a reducing sugar.

Reduction to alcohols - By hydrogenation with H2, Ni, or EtOH/H2O, the C=O groups in open-chain carbohydrates can be converted into alcohols. Alditols are the products.

Biological role

In both plants and animals, carbohydrates can be found nearly everywhere. Besides serving as food reserves in plants and animals, carbohydrates from the skeleton are also a source of energy. The energy derived from oxidation is important for diverse metabolic processes.

They perform the following functions:
  • Carbohydrates are used as an accessible energy source by living organisms. All living beings consume the largest amount of energy (4kcal/gram) from fruits and vegetables.
  • Many animals utilize carbohydrates as the primary energy source, along with being instant sources of energy. As a result of glycolysis/Kreb's cycle, glucose is broken down into ATP.
  • The molecule serves as a fuel, a source of energy, and a metabolic intermediate. In animals, glycogen is stored as starch; in plants, starch is stored as glycogen.
  • The energy stored in carbohydrate is used instead of protein.
  • As the cell wall of plants and microbes, they serve as structural and protective components. Bacteria have peptidoglycan or murein cell wall components, while plants have cellulose and animals have chitin.
  • Proteins and fats are produced through the biosynthesis of carbohydrates.
  • In addition to regulating nerve tissue, carbohydrates provide energy to the brain.
  • The carbohydrate component of antigens, receptor molecules, vitamins, and antibiotics are formed when carbohydrates are combined with lipids and proteins.
  • The production of the RNA and DNA structural frameworks (ribonucleic and deoxyribonucleic acids).
  • They are interconnected with various proteins and lipids. Cells and other elements in the cellular environment interact through the use of these linked carbohydrates.
  • Connective tissue is mainly composed of these carbohydrates.
  • Constipation can be prevented by eating carbohydrates rich in fiber.
  • Fiber also helps in modulating the immune system.
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