DEFINITION,COMPOSITION,CLASSIFICATION ,STRUCTURE AND FUNCTIONS OF CARBOHYDRATES.

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Definition

  -Defined as optically active polyhydroxy aldehydes or ketones

 Example of Carbohydrates 

  - Monosaccharides - Glucose, galactose, glycerose, erythrose, ribose, ribulose, fructose.

 - Oligosaccharides - Maltose, lactose, sucrose, raffinose, stachyose.

 - Polysaccharides - Starch, glycogen, cellulose, pectin, inulin, hyaluonic acid. 

 Foods rich in carbohydrates are referred to as strachy foods. They are found in legumes, starchy vegetables, whole-grain breads and cereals. They also occur naturally with vitamins and minerals in foods like milk, fruits, and milk products. They are alsdo found in refined and processed products like candy, carbonated beverages, and table sugar

Composition

Carbohydrate is an organic compound, it comprises of only oxygen, carbon and hydrogen. 

 - The oxygen: hydrogen ratio is usually is 2:1.

 - The empirical formula being Cn(H2O)n .

 - Carbohydrates are hydrates of carbon; technically they are polyhydroxy aldehydes and ketones.

 - Carbohydrates are also known as saccharides, the word saccharide comes from Greek word sakkron which means sugar.

Classification and nomenclature of carbohydrates

 - The carbohydrates are divided into three major classes depending upon whether or not they undergo hydrolysis and if they do, on the number of products formed.

 1. Monosaccharides: The monosaccharides are polyhydroxy aldehydes or polyhydroxy ketones which cannot be decomposed by hydrolysis to give simpler carbohydrates. e.g. Glucose, fructose, Galactose etc. 

2. Oligosaccharides: The oligosaccharides (Oligo: few) are carbohydrates which yield a definite number (2-9) of monosaccharide molecules on hydrolysis.

a) Disaccharides - Which yield two monosaccharides molecules on hydrolysis. e.g. Sucrose, maltose etc

b)Trisaccharides - Which yield three monosaccharides molecules on hydrolysis 

c)Tetrasaccharides - Which yield four monosaccharides molecules on hydrolysis .

                     eg: Stachyose [gal(α1→6)gal(α1→6)glu(α1↔2β)fru]

 3. Polysaccharides: The carbohydrates which have higher molecular weight, which yield many monosaccharide molecules on hydrolysis. E.g. Starch, glycogen, Dextrin, Cellulose etc


 

In general monosaccharides and oligosaccharides are crystalline solids, soluble in water and sweet to taste, they are collectively known as sugars, the polysaccharides on the other hand are amorphous, insoluble in water and tasteless, they are called non-sugars.

Properties of Carbohydrates 

- General properties of carbohydrates

  •  Carbohydrates act as energy reserves, also stores fuels, and metabolic intermediates. 
  •  Ribose and deoxyribose sugars forms the structural frame of the genetic material, RNA and DNA.
  •   Polysaccharides like cellulose are the structural elements in the cell walls of bacteria and plants. 
  •  Carbohydrates are linked to proteins and lipids that play important roles in cell interactions.
  •   Carbohydrates are organic compounds; they are aldehydes or ketones with many hydroxyl groups. 

- Physical Properties of Carbohydrates 

  •  Steroisomerism - Compound shaving same structural formula but they differ in spatial configuration. Example: Glucose has two isomers with respect to penultimate carbon atom. They are Dglucose and L-glucose. 
  •  Optical Activity - It is the rotation of plane polarized light forming (+) glucose and (-) glucose. 
  •  Diastereo isomeers - It the configurational changes with regard to C2, C3, or C4 in glucose. Example: Mannose, galactose. 
  •  Annomerism - It is the spatial configuration with respect to the first carbon atom in aldoses and second carbon atom in ketoses.

 - Chemical Properties of Carbohydrates 

  •  Ozazone formation with phenylhydrazine. 
  •  Benedicts test.
  •   Oxidation 
  •  Reduction to alcohols 

Structure of Carbohydrates 

 There are three types of structural representations of carbohydrates: 

  • Open chain structure.
  •  Hemi-acetal structure. 
  • Haworth structure



Functions of Carbohydrates 

  •  Carbohydrates are chief energy source, in many animals; they are instant source of energy. Glucose is broken down by glycolysis/ kreb's cycle to yield ATP. 
  •  Glucose is the source of storage of energy. It is stored as glycogen in animals and starch in plants. 
  •   Stored carbohydrates act as energy source instead of proteins. 
  •   Carbohydrates are intermediates in biosynthesis of fats and proteins. 
  •   Carbohydrates aid in regulation of nerve tissue and are the energy source for brain. 
  •   Carbohydrates get associated with lipids and proteins to form surface antigens, receptor molecules, vitamins and antibiotics. 
  •   They form structural and protective components, like in cell wall of plants and microorganisms.
  •   In animals they are important constituent of connective tissues. 
  •  They participate in biological transport, cell-cell communication and activation of growth factors. 
  •  Carbohydrates those are rich in fibre content help to prevent constipation.
  •   Also they help in modulation of immune system.



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