Carbohydrates
Introduction:
Early chemists noticed that carbohydrates had molecular formula could be represented as Cx(H2O)y.
Carbohydrates are considered as compounds in which carbon is surrounded by water molecules; hydrates of carbon, hence the name carbohydrates.
e.g.Glucose C6H12O6 is considered as C6(H2O)6 nd sucrose C12H22O11 is considered as C12(H2O)11.
Later studies revealed that thses compounds which fit in this formula are not classified as carbohydrates.
e.g. Formaldehyde HCHO, Acetic acid CH3COOH, fit into this formula but are not carbohydrates,
Rhamnose C6H12O6 does not fit into this formula but is a carbohydrates. Howsoever the term 'Carbohydrate' persists but now with a different meaning.
Definition of Carbohydrates:
Carbohydrates are optically active polyhydroxy aldehyde or polyhydroxy ketones.
OR
The compounds that can be hydrolysed to polyhydroxy aldehyde or polyhydroxy ketones.
Classification of Carbohydrates:
Carbohydrates are classified on the basis of their behavior on hydrolysis broadly as-
a) Simple Carbohydrates b) Complex Carbohydrates.
a) Simple Carbohydrates:
Simple carbohydrates are known as monosaccharides. A carbohydrates that cannot be hydrolysed further to any simpler sugar is called monosaccharide.
Monosaccharides are the basic unit of all carbohydrates. About twenty monosaccharides are known to occur in nature.
Monosaccharides are further classified as-
1) Aldoses, containing aldehyde group
2) Ketoses, containing keto group.
Depending upon number of carbon atoms, monosaccharides are further classified as triose, tetrose, pentose, hexose etc.
Glucose:
Glucose occurs in ripe grapes (hence the name grape sugar) and in most of the sweet fruits. It is also present in honey and is an essential component of human blood.
In combined form, it is present in cane sugar and in polysaccharides like starch and cellulose. It is probably the most abundant organic compound on earth. Glucose is pentahydroxy aldehyde containing four chiral carbon atoms. Naturally occurring glucose is dextrorotatory and is known as dextrose.
b) Complex carbohydrates:
Complex carbohydrates are further classified as Oligosaccharides and polysaccharides.
A) Oligosaccharides:
A carbohydrates that on hydroysis yields two to ten monosaccharide unit is called Oligosaccharide. Depending upon number of monosaccharide units they yield on hydrolysis, oligosaccharides are further classified as disaccharides, trisaccharides, tetrasaccharides etc.
Disaccharides (C12H22O11) :
A disaccharide has molecular formula C12H22O11 and on hydrolysis gives two molecules of same Or different monosaccharides.
In a disaccharide, anomeric carbon of one monosaccharide molecule is bonded to acarbonic of another monosaccharide molecule through an oxygen atom. Such a linkage between two monosaccharide molecules through oxygen molecule is called Glycosidic linkage.
Sugars that are full acetala are stable to Tollen's reagent, as cyclic form cannot open to the free carbonyl compound and these sugars are non reducing, called glycosides. Their names end in the 'oside' suffix.
[ In general a sugar whose name ends with the suffix 'oside' is non reducing and the one with 'ose' is a reducing sugar].
1) Structure of Sucrose:
Sucrose is known as cane sugar or common table sugar. In sucrose
C-1 of alpha-D-glucopyranose is linked to C-2 of beta-D-Fructofuranose by glycosidic linkage.
The reducing groups of glucose and fructose are involved in glycosidic bond formation, hence sucrose is non-reducing sugar.
On hydrolysis sucrose gives equimolar mixture of dextrorotatory glucose and laevorotatory fructose.
2) Structure of Maltose:
Maltose is obtained by partial hydrolysis of starch. In maltose, C-1 of one alpha-D-glucopyranose is linked to C-4 of another alpha-D-glucopyranose molecule by glycosidic linkage. Thus maltose contains 1-4 alpha glycosidic bond.
Maltose is a reducing sugar because a free aldehyde group can be produced at C-1 in second molecule.
3) Structure of Lactose:
Lactose is known as milk sugar. In lactose C-1 of beta-D-galactopyranose is linked to C-4 of beta-D-glucopyranose by glycosidic linkage. Thus lactose also contains 1-4 beta glycosidic bond.
Lactose is also a reducing sugar because a free aldehyde group can be produced at C-1 in beta-D-glucopyranose molecule.
B) Polysaccharides:
In polysaccharides, a large number of same or different monosaccharides are linked together by glycosidic linkages. They have molecular formula (C6H10O5)n.
A carbohydrates that on hydrolysis yields large number of monosaccharide units is called polysaccharide. Thus they are natural biopolymer of monosaccharide. e. g. Starch, cellulose, glycogen, gums, etc.
1) Structure of Starch:
Starch is an important part of our diet and is mainly found in cerenal grains, roots, tubers, corns, potatoes etc.
Starch is a polymer of alpha-D-glucopyranose and consists of two fractions, amylose and amylopectin. Amylose is water soluble component and constitutes about 20% of starch.
In amylose about 200-1000 alpha-D-glucopyranose molecules are linked together by glycosidic linkage between C-1 of one unit and C-4 of another unit. It is a long chain unbranched polymer. Thus amylose contains 1-4 alpha glycoside bonds like those in maltose.
Amylopectin is insoluble in water and constitutes about 80% of starch. It is a branched chain polymer. In amylopectin, alpha-D-glucopyranose molecules are linked together by glycosidic linkage between C-1 of one unit and C-4 of another unit to form long chain.
Branching occurs by the formation of a glycosidic linkage between C-1 on one glucopyranose unit and C-6 of another glucopyranose unit. Thus amylopectin contains 1-alpha glycoside bonds in long chain and 1-6 alpha glycosidic branches.
2) Structure of cellulose:
Cellulose is the principle component of plant structure viz. Wood, cotton to support the weight of the plant. Cell wall of plant cells is made up of cellulose. Cellulose is a long chain unbranched polymer.
In cellulose, beta-D-glucopyranose molecules are linked together by glycosidic linkage between C-1 of one unit and C-4 of another unit to form long chain. Thus cellulose contains 1-4 beta glycosidic linkages like those in cellobiose.
Long cellulose molecules, called microbifils which are held together by hydrogen bonding between many OH groups of Glucose ring and form bundles.
Humans cannot use it directly as a food as they cannot hydrolyse cellulose, but certain bacteria and protozoa can hydrolyse it. Humans cannot hydrolyse cellulose due to lack of the enzyme required for hydrolysis.
3) Structure of Glycogen:
In animal body, glucose is stored in the form of glycogen. Glycogen is known as 'animal starch, since it's structure is similar to amylopectin.
The branching in glycogen is more extensive than in amylopectin. In the highly branched structure of glycogen there are end groups available for quick hydrolysis to provide the glucose needed for metabolism. It is then used as instant energy.
Importance of Carbohydrates:
Carbohydrates are the most abundant organic constituents in plants. They serve as an important source of chemical energy for living organisms. They are important constitutes of supporting tissues in plants e. g. Cellulose found in wood, cotton, flex etc.
Plants synthesize carbohydrates by photosynthesis and animals get carbohydrates from plants in the form of starch and sugar. Animals store glucose in the form of glycogen which is their principle source of energy.
We encounter carbohydrates at almost every turn of our daily life. The paper on which this book is printed is largely cellulose; so too is cotton of our clothes and the wood of our houses.
The flour bread is mainly starch, which is also a major constitutes of many other foodstuffs such as potatoes, rice, beans, corn, peas, etc. Thus carbohydrates satisfy our three basic needs; food, clothes and shelter.
Introduction:
Early chemists noticed that carbohydrates had molecular formula could be represented as Cx(H2O)y.
Carbohydrates are considered as compounds in which carbon is surrounded by water molecules; hydrates of carbon, hence the name carbohydrates.
e.g.Glucose C6H12O6 is considered as C6(H2O)6 nd sucrose C12H22O11 is considered as C12(H2O)11.
Later studies revealed that thses compounds which fit in this formula are not classified as carbohydrates.
e.g. Formaldehyde HCHO, Acetic acid CH3COOH, fit into this formula but are not carbohydrates,
Rhamnose C6H12O6 does not fit into this formula but is a carbohydrates. Howsoever the term 'Carbohydrate' persists but now with a different meaning.
Definition of Carbohydrates:
Carbohydrates are optically active polyhydroxy aldehyde or polyhydroxy ketones.
OR
The compounds that can be hydrolysed to polyhydroxy aldehyde or polyhydroxy ketones.
Classification of Carbohydrates:
Carbohydrates are classified on the basis of their behavior on hydrolysis broadly as-
a) Simple Carbohydrates b) Complex Carbohydrates.
a) Simple Carbohydrates:
Simple carbohydrates are known as monosaccharides. A carbohydrates that cannot be hydrolysed further to any simpler sugar is called monosaccharide.
Monosaccharides are the basic unit of all carbohydrates. About twenty monosaccharides are known to occur in nature.
Monosaccharides are further classified as-
1) Aldoses, containing aldehyde group
2) Ketoses, containing keto group.
Depending upon number of carbon atoms, monosaccharides are further classified as triose, tetrose, pentose, hexose etc.
Glucose:
Glucose occurs in ripe grapes (hence the name grape sugar) and in most of the sweet fruits. It is also present in honey and is an essential component of human blood.
In combined form, it is present in cane sugar and in polysaccharides like starch and cellulose. It is probably the most abundant organic compound on earth. Glucose is pentahydroxy aldehyde containing four chiral carbon atoms. Naturally occurring glucose is dextrorotatory and is known as dextrose.
b) Complex carbohydrates:
Complex carbohydrates are further classified as Oligosaccharides and polysaccharides.
A) Oligosaccharides:
A carbohydrates that on hydroysis yields two to ten monosaccharide unit is called Oligosaccharide. Depending upon number of monosaccharide units they yield on hydrolysis, oligosaccharides are further classified as disaccharides, trisaccharides, tetrasaccharides etc.
Disaccharides (C12H22O11) :
A disaccharide has molecular formula C12H22O11 and on hydrolysis gives two molecules of same Or different monosaccharides.
In a disaccharide, anomeric carbon of one monosaccharide molecule is bonded to acarbonic of another monosaccharide molecule through an oxygen atom. Such a linkage between two monosaccharide molecules through oxygen molecule is called Glycosidic linkage.
Sugars that are full acetala are stable to Tollen's reagent, as cyclic form cannot open to the free carbonyl compound and these sugars are non reducing, called glycosides. Their names end in the 'oside' suffix.
[ In general a sugar whose name ends with the suffix 'oside' is non reducing and the one with 'ose' is a reducing sugar].
1) Structure of Sucrose:
Sucrose is known as cane sugar or common table sugar. In sucrose
C-1 of alpha-D-glucopyranose is linked to C-2 of beta-D-Fructofuranose by glycosidic linkage.
The reducing groups of glucose and fructose are involved in glycosidic bond formation, hence sucrose is non-reducing sugar.
On hydrolysis sucrose gives equimolar mixture of dextrorotatory glucose and laevorotatory fructose.
2) Structure of Maltose:
Maltose is obtained by partial hydrolysis of starch. In maltose, C-1 of one alpha-D-glucopyranose is linked to C-4 of another alpha-D-glucopyranose molecule by glycosidic linkage. Thus maltose contains 1-4 alpha glycosidic bond.
Maltose is a reducing sugar because a free aldehyde group can be produced at C-1 in second molecule.
3) Structure of Lactose:
Lactose is known as milk sugar. In lactose C-1 of beta-D-galactopyranose is linked to C-4 of beta-D-glucopyranose by glycosidic linkage. Thus lactose also contains 1-4 beta glycosidic bond.
Lactose is also a reducing sugar because a free aldehyde group can be produced at C-1 in beta-D-glucopyranose molecule.
B) Polysaccharides:
In polysaccharides, a large number of same or different monosaccharides are linked together by glycosidic linkages. They have molecular formula (C6H10O5)n.
A carbohydrates that on hydrolysis yields large number of monosaccharide units is called polysaccharide. Thus they are natural biopolymer of monosaccharide. e. g. Starch, cellulose, glycogen, gums, etc.
1) Structure of Starch:
Starch is an important part of our diet and is mainly found in cerenal grains, roots, tubers, corns, potatoes etc.
Starch is a polymer of alpha-D-glucopyranose and consists of two fractions, amylose and amylopectin. Amylose is water soluble component and constitutes about 20% of starch.
In amylose about 200-1000 alpha-D-glucopyranose molecules are linked together by glycosidic linkage between C-1 of one unit and C-4 of another unit. It is a long chain unbranched polymer. Thus amylose contains 1-4 alpha glycoside bonds like those in maltose.
Amylopectin is insoluble in water and constitutes about 80% of starch. It is a branched chain polymer. In amylopectin, alpha-D-glucopyranose molecules are linked together by glycosidic linkage between C-1 of one unit and C-4 of another unit to form long chain.
Branching occurs by the formation of a glycosidic linkage between C-1 on one glucopyranose unit and C-6 of another glucopyranose unit. Thus amylopectin contains 1-alpha glycoside bonds in long chain and 1-6 alpha glycosidic branches.
2) Structure of cellulose:
Cellulose is the principle component of plant structure viz. Wood, cotton to support the weight of the plant. Cell wall of plant cells is made up of cellulose. Cellulose is a long chain unbranched polymer.
In cellulose, beta-D-glucopyranose molecules are linked together by glycosidic linkage between C-1 of one unit and C-4 of another unit to form long chain. Thus cellulose contains 1-4 beta glycosidic linkages like those in cellobiose.
Long cellulose molecules, called microbifils which are held together by hydrogen bonding between many OH groups of Glucose ring and form bundles.
Humans cannot use it directly as a food as they cannot hydrolyse cellulose, but certain bacteria and protozoa can hydrolyse it. Humans cannot hydrolyse cellulose due to lack of the enzyme required for hydrolysis.
3) Structure of Glycogen:
In animal body, glucose is stored in the form of glycogen. Glycogen is known as 'animal starch, since it's structure is similar to amylopectin.
The branching in glycogen is more extensive than in amylopectin. In the highly branched structure of glycogen there are end groups available for quick hydrolysis to provide the glucose needed for metabolism. It is then used as instant energy.
Importance of Carbohydrates:
Carbohydrates are the most abundant organic constituents in plants. They serve as an important source of chemical energy for living organisms. They are important constitutes of supporting tissues in plants e. g. Cellulose found in wood, cotton, flex etc.
Plants synthesize carbohydrates by photosynthesis and animals get carbohydrates from plants in the form of starch and sugar. Animals store glucose in the form of glycogen which is their principle source of energy.
We encounter carbohydrates at almost every turn of our daily life. The paper on which this book is printed is largely cellulose; so too is cotton of our clothes and the wood of our houses.
The flour bread is mainly starch, which is also a major constitutes of many other foodstuffs such as potatoes, rice, beans, corn, peas, etc. Thus carbohydrates satisfy our three basic needs; food, clothes and shelter.
