Question

Conclusion about Monosaccharides, Disaccharides and Polysaccharides

Answer 1

Ans.

Monosaccharides-

• also known as simple sugars.
• Simplest carbohydrate.
• General formula is C_nH_2nO. usually have 3-7 carbon atoms per molecule.
• Classified on the basis of carbon no. As -

Carbon no.	sugar name	example
3	Trioses	glyceradehyde
4	Tetroses	Erythrose
5	Pentoses	Ribose
6	Hexoses	Glucose
7	Heptose	Sedoheptulose

functions -

• intermediates in photosynthesis like glyceradehyde,ribulose etc.
• glucose act as main fuel in all cells
• Monosaccharides are the building blocks for a)disaccharides like lactose and sucrose b) polysaccharides like cellulose.
• components of macromolecules like ribose is a component of RNA, NAD and NADP etc.

​​​​​​​Disaccharides-

• most abundant oligosaccharides in the cells.
• Have two monosaccharide units joined by glycosidic bond. The joining process involves loss of water called dehydration and is called condensation
• also called double sugars.

Examples of disachharides are -

• Maltose- composed of 2 glucose molecules.Formed in the germinating starchy seeds and malt. So also called malt sugar.
• ​​​​​​​Sucrose- commonly called cane or table sugar. Formed of a glucose and fructose molecule. It is the storage product of photosynthesis.
• lactose-also called milk sugar. Composed of one glucose and one galactose molecule.

​​​​​​​Polysaccharides-

• consists of more than six (often numerous) molecules of a monosaccharide. The latter are joined together by glycosidic bond with a loss of water each time a monosaccharide molecule is added.
• general formula for polysaccharides is (C₆H₁₀O₅)_n where n stands for unknown no. Of monosaccharide molecules.

​​​​​​​Structural classification regarding their composition-

1. Homopolysaccharides- composed of normal monosaccharide molecules of a single type. Ex - glycogen, starch and cellulose. All these are made up of glucose units. Similarly, Agar is a homopolysaccharide of galactose monomers.
2. Heteropolysaccharides- are composed of modified monosaccharide molecules of different types. Examples-

• ​​​​​​​Mucopolysaccharides- These are polymers of modified sugars (galactose and mannose) called sugar acids and amino sugars. hyaluronic acid, heparin, chondroitin sulfate and keratin sulfate well known examples of mucopolysaccharides.
• Mucoproteins( glycoproteins) - ​​​​​​​these are compounds of mucopolysaccharides and proteins. They contains acetylglucosamine, acetylgalactosamine, and hexose sugars (mannose or galactose) or their derivatives.Blood group substances A,B and Rh antigens of RBCs ,LH ,mucus are all glycoproteins.
• Chitin- present in exoskeleton of arthropods and in the cell wall of fungi. It is a nitrogen containing polysaccharide made up of acetylglucosamine molecules joined by glycosidic bonds.
• Peptidoglycan- composed of polysaccharide chains connected by cross links of small peptides made of 4 amino acid units.The polysaccharide chain is formed of disachharide units joined together into a long unbranched molecule. The disaccharide unit itself made of 2 sugar derivatives- acetylglucosamine and acetylmuramic acid. peptidoglycan is present in cell wall of bacteria and blue green algae.