Monosaccharides
Monosaccharide is formed from the Greek word mono meaning one and saccharin meaning sugar. Monosaccharide means a single sugar. Carbohydrates that do not yield any other simple carbohydrate units when broken down or analyzed are called monosaccharides. Their common symbol is CnH2nOn. Monosaccharides have 3-10 carbons. Monosaccharides have a free aldehyde group (-CHO) at carbon 1 or a ketone group (>C=O) at carbon 2, so they are called reducing sugars or reducing sugars. Monosaccharides with aldehyde groups are called aldoses and monosaccharides with ketone groups are called ketoses. Aldehyde and ketone groups are reducing groups and sugars containing reducing groups are called reducing sugars.
Characteristics of monosaccharides
(i) It is a simple sugar.
(ii) It is photoactive.
(iii) It is a small molecule.
(iv) Its molecular weight is less than 10,000 daltons.
(v) It has a sweet taste.
(vi) It is granular and soluble in water.
(vii) It contains aldehyde and ketone groups.
(viii) It is called aldose or ketose sugar.
(ix) It is a repulsive sugar.
Classification of Monosaccharides
Monosaccharides can be divided into two groups based on the aldehyde or ketone group.
1. Aldose: Monosaccharides containing aldehyde groups are called aldoses. Such as glucose, erythrose, ribose, mannose etc. Dr. Siddiq Publications
2. Ketose: Monosaccharides containing ketone group are called ketose. Such as fructose, erythrulose, ribulose, dihydroxyacetone etc.
The different types of monosaccharides based on the number of carbons are-
1. Triose: Monosaccharides with three carbons are called triose. A triose with an aldehyde group is called an aldotriose and a ketone group with a ketotriose. Its molecular symbol is C3H6O3. For example, glyceraldehyde, dihydroxy acetone etc.
2. Tetrose: A four-membered monosaccharide is called a tetrose. Its molecular symbol is C4H8O4. A tetrose with a four-carbon aldehyde group is called an aldotetrose and a ketone group with a ketotetrose. Eg-Erythrose, Thirose, Erythrolose etc. Dr. Siddiq Publications
3. Pentose: Five carbon monosaccharides are called pentoses. Its molecular symbol is C5H10O5. Ribose and deoxyribose are pentose sugars and form nucleotides and nucleic acids. Examples – ribulose, xylulose, arabinose, lyxose, ribose, deoxyribose etc. Dr. Siddiq Publications
4. Hexose: Monosaccharides with six carbons are called hexoses. Its molecular symbol is C6H12O6. Hexoses of aldehyde groups are called aldohexoses and hexoses of ketone groups are called ketohexoses. They are known as blood sugar. There are 16 types of hexoses. The abundant hexose is the glucose that provides energy to living cells. Examples – glucose, fructose, galactose, mannose etc.
5. Heptose: A monosaccharide with seven carbons is called heptose. Its molecular symbol is C7H14O7. Its number is very less. It plays an important role in photosynthesis. Pseudoheptulose, monoheptulose etc.
6. Octose: An eight carbon monosaccharide is called octose. Its molecular symbol is C8H26O8. eg glucooctose. Dr. Siddiq Publications
7. Nenose: A monosaccharide having nine carbons is called nenose. Its molecular symbol is C9H18O9. eg gluconanose.
8. Decose: A ten carbon monosaccharide is called decose. Its molecular symbol is C10H30O10. E.g. Glucodecose.
Disaccharide
Carbohydrates that break down or break down into two molecules of monosaccharides are called disaccharides. Their chemical symbol is C12H22O11. A condensation reaction between two monosaccharide molecules results in the removal of one molecule of H2O from two –OH groups to form a disaccharide. Both monosaccharide molecules of the disaccharide form new C-O-C bonds. The C-O-C bond formed is called a glycosidic bond. Disaccharides such as sucrose (table sugar), maltose, isomaltose, lactose (milk sugar), cellobiose, trehalose etc. When sucrose or sugar is broken down, glucose and fructose are obtained. Again, lactose is broken down to glucose and galactose. Dr. Siddiq Publications
Oligosaccharide
The word oligosaccharide is formed from the Greek words oligo meaning few and saccharin meaning sugar. Oligosaccharide means few sugars. Carbohydrates that break down or break down into a few molecules of monosaccharides (3-10 molecules) are called oligosaccharides. Monosaccharides or monomers are linked by glycosidic bonds to form oligosaccharides. The attachment of the hydroxyl group of one monosaccharide to the hydroxyl group of another monosaccharide is called glycosidic linkage. Dr. Siddiq Publications
Properties of oligosaccharides
(i) Oligosaccharides are simple sugars.
(ii) It can be wet analyzed.
(iii) It is a small molecule.
(iv) Its molecular weight is less than 10,000 daltons.
(v) It has a sweet taste.
(vi) It is granular and soluble in water.
(vii) It is an insoluble sugar.
Some oligosaccharides
(i) Trisaccharides: Carbohydrates which break down or break down into three molecule monosaccharides are called trisaccharides. Such as – raffinose, rabinose, raminose and malizitose. Breaking down raffinose yields glucose, fructose and galactose. Dr. Siddiq Publications
(ii) Tetrasaccharides: Carbohydrates which break down or break down into four molecules of monosaccharides are called tetrasaccharides. Its chemical symbol is C24H42O21. Eg – Stachyose, Skardose etc. When stachyose is broken down, glucose, fructose and two molecules of galactose are obtained. Tetrasaccharides are found in plants of the Leguminosae and Labiatae families. Cucurbita pepo plant contains tetrasaccharides.
(iii) Pentasaccharides: Carbohydrates which break down or break down into monosaccharides of five molecules are called pentasaccharides. For example, verbose. The root of Verbescus thepus plant contains pentasaccharides.
(iv) Hexasaccharide: Carbohydrates composed of six monosaccharide molecules are called hexasaccharides. For example, α-Cyclodextrin.
(v) Heptasaccharides: Carbohydrates which are made up of seven molecules of monosaccharides are called heptasaccharides.
(vi) Octasaccharides: Carbohydrates which are composed of eight molecules of monosaccharides are called octasaccharides.
(vii) Nanasaccharides: Non-carbohydrate molecules composed of monosaccharides are called Nanasaccharides.
(viii) Decasaccharides: Carbohydrates which are composed of ten molecules of monosaccharides are called Decasaccharides.
Polysaccharide
Polysaccharide is formed from the Greek words poly meaning many and saccharin meaning sugar. Carbohydrates that break down or break down into many molecules (more than 10) of monosaccharides are called polysaccharides. Their common symbol is (C6H10O5)n. where 10 ≥ n ≤ 3000|
Properties of polysaccharides
(i) It is a complex sugar.
(ii) Its wet analysis yields numerous monosaccharide molecules.
(iii) It is a large molecule.
(iv) Its molecular weight is more than 10,000 daltons.
(v) It is not sweet in taste.
(vi) It is non-granular and insoluble in water.
(vii) It does not contain aldehyde and ketone groups.
(viii) It is an insoluble sugar.
1. Classification based on work
are divided into three categories based on function.
(i) Stored polysaccharides: All the carbohydrates that are stored in the body as stored food are called stored polysaccharides. For example, starch, glycogen, inulin, dextin, paramylam, livan etc. Starch is the main stored food in plants and glycogen in animals. Dr. Siddiq Publications
(ii) Structural polysaccharides: Carbohydrates which form the cell walls of plants are called structural polysaccharides. For example, cellulose, hemicellulose, pectic acid, chitin, keratin sulfate etc. Cellulose is the main structural component of the cell wall.
(iii) Complex polysaccharides: Those polysaccharides which are composed of sugars and non-sugars are called complex polysaccharides. Such as mucopolysaccharide, agar, hyaluronic acid, chondroitin sulfate, heparin etc. Dr. Siddiq Publications
2. Structural classification
Polysaccharides are divided into two categories based on structure.
(i) Homopolysaccharides or Homoglycans: Carbohydrates that are composed of monosaccharides of the same type are called homopolysaccharides or homoglycans. For example, starch, cellulose, glycogen, inulin etc.
(ii) Heteropolysaccharides or Heteroglycans: Carbohydrates composed of two or more types of monosaccharides are called heteropolysaccharides or heteroglycans. Such as hemicellulose, mucopolysaccharide, pectin, chitin, agar etc.
3. Unit Based Classification: On the basis of structural unit polysaccharides are of several types-
(i) Glucosan: The polysaccharide formed from glucose is called glucosan.
(ii) Fructosan: The polysaccharide formed by fructose is called fructosan.
(iii) Galactasan: The polysaccharide formed by galactose is called galactasan.
(iv) Hexosan: A polysaccharide composed of six carbon monosaccharides is called hexosan.