Carbohydrates - Definition,Functions,Classification

 Definition :

•Aldehyde or Ketone compounds with multiple hydroxyl groups

                                                             Or

•The aldehyde or ketone derivatives of polyhydroxy alcohols.

•The General molecular formula is Cn(H2O)n

• They are readily soluble in water because of the presence of multiple hydroxyl groups

•They are sweet and hence called as sugars and are also called ‘’saccharides’’(Greek, saccharin means sugar)

Functions of Carbohydrates

• Serve as the primary source of energy, e.g., Glucose
• Serve as a storage form of energy, e.g., Glycogen in animal tissue and starch in plants
• Serve as a structural component of many organisms, e.g., Glycosaminoglycans in humans, cellulose in plants, and chitin in insects
• Serve as dietary fibers,e.g., Non-digestible carbohydrates like cellulose,
• Serve as a constituent of nucleic acids RNA and DNA, e.g., Ribose and deoxyribose sugar
• They play a role in lubrication, cellular intercommunication, and immunity
• They are also involved in detoxification, e.g., Glucuronic acid.

Classification Of Carbohydrates

§  Based on the number of sugar units, carbohydrates are mainly classified into three groups :

I.Monosaccharides (Greek: Mono = one)

§ Also called simple sugars - made of one sugar unit

§They cannot be further hydrolyzed into a simpler form because they consist of only a single polyhydroxy aldehyde or ketone unit,

§ Subdivided into two groups

§  Classification of monosaccharides based on the number of carbon and the type of functional group

II.Oligosaccharides (Greek: oligo = few)

§  Consist of a short chain of monosaccharide units (2 to 10 units).

§  Joined together by a characteristic bond called a glycosidic bond

§  On hydrolysis, gives two to ten molecules of simple sugar (monosaccharide) units

Subdivided into different groups based on the number of monosaccharide units present

III.Polysaccharides (Greek: Poly = many) or Glycans

§  They are Polymers consisting of hundreds or thousands of monosaccharide units.

§  Also called glycans or complex carbohydrates

§  May be either linear or branched in structure.

§  Have high molecular weight

§  Only sparingly soluble in water.

§  Not sweetish in taste 

§  Do not exhibit any of the properties of aldehyde or ketone group.

Polysaccharides are of two types