There are roughly 92 naturally occurring elements on earth, but interestingly, only 4 (oxygen, carbon, hydrogen and nitrogen) make about 96% of the mass of the human body. These elements combine to form life-sustaining biomolecules, which can be divided into four groups: carbohydrates, lipids, proteins, and nucleic acids. Carbohydrates, proteins, and lipids are used by cells as the building blocks for cells or for energy, while nucleic acids are the basis of the genetic material. Carbohydrates are the most abundant of the biomolecules.
There are three major classes of carbohydrates; monosaccharides, disaccharides, and polysaccharides. This classi!cation is based on how many "subunits make up the molecule. The name "saccharide" is derived from the Greek, meaning sugar.
MONOSACCHARIDES The monosaccharides (mono = one, saccharide = sugar) are the basic subunits of carbohydrates. They contain from 3 to 7 carbons and have the general formula of (CH2O)n where n ranges from 3 to 7 (5 or 6 being the most common). For example, if n = 6, the formula for the monosaccharide would be C6H12O6 and if n = 5 the formula would be C5H10O5. Hopefully, it is obvious that the monosaccharides contain a signi!cant amount of oxygen, one for every carbon in the molecule. Carbohydrates have the highest oxygen to carbon ratio of any of the important organic molecules. Common monosaccharides include: glucose, fructose, galactose, ribose, and deoxyribose. Notice that the name of each of these sugars ends with the su"x -ose. This su"x, -ose, means full, speci!cally, full of oxygen. The names of most all sugars will end with this su"x.
Disaccharides (Di = 2, saccharide = sugar) are formed when two monosaccharide molecues are linked together. As shown in the figure below, when the two monosaccharides are linked together, one of the products of the reaction is water. Because water is removed to link the subunits together, the reaction is called a dehydration synthesis reaction. This is a common type of synthesis reaction that we will see again when we learn about the formation of lipids and proteins.
Polysaccharides are long chains of monosaccharide subunits linked together through dehydration synthesis reactions. These chains may number from as few as three subunits to thousands. The polysaccharides are what we refer to as complex carbohydrates. Based on their function, polysaccharides can be classified as either storage molecules, or structural molecules. Storage polysaccharides include starch and glucogen. Starch is a large polymer of glucose subunits and is the storage form of glucose in plants. Sources include seeds, grains, corn, beans, potatoes, and rice.
Oligosaccharides consist of galacto-oligosaccharides, fructo-oligosaccharides, and mannan-oligosaccharides that cannot be digested by pancreatic or intestinal enzymes, but are soluble in 80% ethanol . Galacto-oligosaccharides, or α-galactosides, that are present in large amounts in legumes, are comprised of raffinose, stachyose, and verbascose, which have a structure consisting of a unit of sucrose linked to one, two, or three units of D-galactose, respectively. These oligosaccharides cause flatulence in pigs and humans due to the lack of an enzyme, α-galactosidase, that hydrolyzes the glycosidic bonds linking the monosaccharides that constitute these α-galactosides and are, therefore, utilized by bacteria in the large intestine. In raffinose, D-galactose is linked to sucrose by an α-(1,6) bond, whereas two units and three units of D-galactose are linked to sucrose, also via α-(1,6) glycosidic bonds, in stachyose and verbascose, respectively. Transgalacto-oligosaccharides are another type of galacto-oligosaccharides that may have prebiotic effects in young pigs and are commercially synthesized from the transglycosylation actions of β-glycosidases on lactose, creating β-(1,6) polymers of galactose linked to a terminal glucose unit via an α-(1,4) glycosidic bond . However, transgalacto-oligosaccharides are not naturally synthesized
MOREOVER, I am providing you short table and also MAP of carbohydrates.