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Carbohydrates
Carbohydrates constitute an important class of compounds like glucose, fructose, sucrose, starch, cellulose, etc which play a vital role in our everyday life. Carbohydrates are also much known as saccharides. Originally, the name carbohydrates was given to the compounds pertaining to general formula Cx(H2O)y, and they were considered to be hydrates of carbon. However, this definition could not hold ground for long due to following reasons:
(i) Many compounds like formaldehyde (CH2O), acetic acid (C2H4O2), confirm to formula Cx(H2O)y but they do not exhibit the characteristic properties of carbohydrates.
(ii) Some carbohydrates like rhamnose (C6H12O5), deoxyribose (C5H10O4) do not conform to the formula Cx(H2O)y, and
(iii) Carbon is not known to form hydrates.
The above facts ultimately gave way to the modern definition of carbohydrates. Carbohydrates are now defined as polyhydroxy aldehydes or polyhydroxy ketones or the compounds which can be hydrolysed to them.
Classification of carbohydrates
Carbohydrates are classified into three major categories depending upon their behavior towards hydrolysis:
1. Monosaccharides: These are simple carbohydrates which cannot be hydrolysed to still simpler carbohydrates. About 20 monosaccharides are known to occur in nature. Glucose and fructose are common examples.
2. Oligosaccharides: These are the carbohydrates which on hydrolysis give two to ten units of monosaccharides. Accordingly, they may be further divided into di, tri or tetrasaccharides depending upon the actual number of monosaccharide units formed by the hydrolysis of a particular oligosaccharide.
Disaccharides give tow units of monosaccharides on hydrolysis. The two monosaccharide units obtained on hydrolysis of a disaccharides may be same or different. Common examples are sucrose and maltose. Both have molecular formula C12H22O11.
Sucrose on hydrolysis gives one molecule of glucose and one molecule of fructose whereas maltose on hydrolysis gives two molecules of glucose only.
Trisaccharides give three units of monosaccharides on hydrolysis. Raffinose, C15H22O16 is a common example.
Tetrasaccharides give four units of monosaccharides on hydrolysis. Stachyose, C24H42O21 is a common example.
3. Polysaccharides: These are the carbohydrates which are polymers molecules and can be hydrolysed to give large number of monosaccharide units. The commonly occurring polysaccharides have the general formula (C6H10O6). The common examples are starch, glycogen and cellulose.
It may be noted that the carbohydrates which are sweet in taste are collectively called sugars while those which are not sweet are called non-sugars. Monosaccharides and disaccharides are sugars but polysaccharides are non-sugars.
The relative degree of sweetness of various sugars is given below in tabular form:
The carbohydrates may also be classified as reducing and non-reducing sugars. The carbohydrates which can reduce Tollen’s reagent of Fehling’s solution are classified as reducing sugars, while which do not reduce these reagents are called non-reducing sugars.
Reducing sugars contain free aldehydes or ketones group. All monosaccharides are reducing sugars. Disaccharides may be reducing or non-reducing. If the carbonyl groups of both the monosaccharides are involved in linkage, the disaccharide is non-reducing. On the other hand, of one of the carbonyl groups is free, the disaccharides is reducing. Sucrose is a non-reducing sugar while maltose is a reducing sugar.
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(i) Many compounds like formaldehyde (CH2O), acetic acid (C2H4O2), confirm to formula Cx(H2O)y but they do not exhibit the characteristic properties of carbohydrates.
(ii) Some carbohydrates like rhamnose (C6H12O5), deoxyribose (C5H10O4) do not conform to the formula Cx(H2O)y, and
(iii) Carbon is not known to form hydrates.
The above facts ultimately gave way to the modern definition of carbohydrates. Carbohydrates are now defined as polyhydroxy aldehydes or polyhydroxy ketones or the compounds which can be hydrolysed to them.
Classification of carbohydrates
Carbohydrates are classified into three major categories depending upon their behavior towards hydrolysis:
1. Monosaccharides: These are simple carbohydrates which cannot be hydrolysed to still simpler carbohydrates. About 20 monosaccharides are known to occur in nature. Glucose and fructose are common examples.
2. Oligosaccharides: These are the carbohydrates which on hydrolysis give two to ten units of monosaccharides. Accordingly, they may be further divided into di, tri or tetrasaccharides depending upon the actual number of monosaccharide units formed by the hydrolysis of a particular oligosaccharide.
Disaccharides give tow units of monosaccharides on hydrolysis. The two monosaccharide units obtained on hydrolysis of a disaccharides may be same or different. Common examples are sucrose and maltose. Both have molecular formula C12H22O11.
Sucrose on hydrolysis gives one molecule of glucose and one molecule of fructose whereas maltose on hydrolysis gives two molecules of glucose only.
Trisaccharides give three units of monosaccharides on hydrolysis. Raffinose, C15H22O16 is a common example.
Tetrasaccharides give four units of monosaccharides on hydrolysis. Stachyose, C24H42O21 is a common example.
3. Polysaccharides: These are the carbohydrates which are polymers molecules and can be hydrolysed to give large number of monosaccharide units. The commonly occurring polysaccharides have the general formula (C6H10O6). The common examples are starch, glycogen and cellulose.
It may be noted that the carbohydrates which are sweet in taste are collectively called sugars while those which are not sweet are called non-sugars. Monosaccharides and disaccharides are sugars but polysaccharides are non-sugars.
The relative degree of sweetness of various sugars is given below in tabular form:
| Sugar | Lactose | Maltose | Galactose | Glucose | Sucrose | Fructose |
| Relative sweetness | 16 | 32 | 32 | 74 | 100 | 173 |
The carbohydrates may also be classified as reducing and non-reducing sugars. The carbohydrates which can reduce Tollen’s reagent of Fehling’s solution are classified as reducing sugars, while which do not reduce these reagents are called non-reducing sugars.
Reducing sugars contain free aldehydes or ketones group. All monosaccharides are reducing sugars. Disaccharides may be reducing or non-reducing. If the carbonyl groups of both the monosaccharides are involved in linkage, the disaccharide is non-reducing. On the other hand, of one of the carbonyl groups is free, the disaccharides is reducing. Sucrose is a non-reducing sugar while maltose is a reducing sugar.
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Inorganic Chemistry
Organic Chemistsry
Analytical Chemistry
Biochemistry
Physical Chemistry
Topics
Nucleic Acid Functions
Carbohydrates
Glucose-Cyclic Structure
Disaccharides
Enzymes
Fructose
Functions Of Carbohydrates
Glucose
Hormones
Enzyme Activity Mechanism
Monosaccharides
Nucleic Acids
Polysaccharides
Proteins, Amino Acids
Proteins Structure
The Cell
Vitamins
Biostatistics
Mutarotation
Monosaccharides Properties
Compound Lipids
Derived Lipids
Fatty Acids
Lipids
Simple Lipids
Radiation-Detection Measurement
Synthetic Polymers
Amino Acids
Bioenergetics
Biological Oxidation Reduction
Cell Membrane
Cell Motility, Cytoskeleton
Cerebrospinal Fluid
Chromatography
Proteins Classification
Clonal Selection Theory
Blood Coagulation
Coenzymes
Nerve Impulse Conduction
Connective Tissue
DNA, RNA
Diagnostic Applications
Lipids-Digestion, Absorption
Proteins-Digestion, Absorption
Endoplasmic Reticulum
Enzyme Inhibition
Enzyme Linked Assay
Enzymes Classification
Erythrocytes
Vitamins-Complex Group
Extracellular Enzymes
Fermentation, Putrefaction
Fibrinolysis
Folic Acid
ATP Functions
Bile Salts Functions
Functions Of Blood
Plasma Proteins Functions
Gastric Juice
Hemoglobin
Blood Lacing Hemolysis
Blood Clotting Inhibitors
Intermediary Metabolism
Enzymes Intracellular Location
Leukocytes
Lymph, Sweat, Synovial Fluid
Histocompatibility
Proteins-Transport Mechanism
Metabolism Study
Mitochondria
Muscles
Niacin
Nucleoproteins
Nucleotides
Nucleus
Oxidative Phosphorylation
Oxyhemoglobin
Pancreatic Juice
Peptides Importance
Proteins Properties
Polyacrylamide Electrophoresis
Amino Acids Properties
DNA Properties
Proteins Characterization
Nucleotide Transhydrogenases
Relaxation
Riboflavin
Saliva
Nucleic Acids Structure
Protein Molecule Structure
Thiamine
Transmission At The Synapse
Transport Across Membranes
Variations In Disease
Vitamin A
Vitamin B
Vitamin C
Vitamin D
Vitamin E
Vitamin K




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