Carbohydrates are organic compounds that consist of carbon, hydrogen,
and oxygen in a 1:2:1 ratio. Cells use different kinds of carbohydrates
as structural materials, for fuel, and for storing and transporting
energy. The three main types of carbohydrates in living systems are
monosaccharides, oligosaccharides, and polysaccharides.
Monosaccharides (one sugar unit) are the simplest type of carbohydrate,
but they have extremely important roles as monomers of larger molecules.
The molecular formula of monosaccharides is (CH2O)n. The number of
carbons (n in the formula above) varies between monosaccharide types,
but for every carbon in a monosaccharide, there is also one
water-molecule equivalent (H2O in the formula). Glucose is the main
“fuel” for bacteria, plants and animal cells.
Monosaccharides are the building blocks of more complex carbohydrates. For example, two monosaccharides can bond to form a disaccharide (two sugar unit).
Examples: Sucrose (glucose+fructose) (Table Sugar)
Lactose (glucose+galactose) (Milk Sugar)
Maltose (glucose+glucose) (figure Right)
Before disaccharides can be used by organisms, they must be broken down into their monosaccharide units. The disaccharides have the molecular formula C12H22O11.
A disaccharide is formed upon the formation of a glycosidic linkage (a type of bond) between monosaccharides. This glycosidic linkage forms via a dehydration synthesis reaction.
The “complex” carbohydrates, or polysaccharides, are straight or branched chains of many sugar monomers, often hundreds or thousands of them. There may be one type or many types of monomers in a polysaccharide (many sugar units). Most macromolecular carbohydrates are polysaccharides. Polysaccharides typically serve as (i) carbon and energy storage molecules (starch, glycogen) or (ii) as structural material (e.g., in plants, insects, and fungi).
Most plants make much more glucose than they can use. The excess is stored as starch inside cells that make up roots, stems, and leaves. Some starches are made of thousands of monosaccharide (glucose) units.
Potatoes, beans, and grains such as rice, corn, and wheat are examples of plants that store large quantities of starch. When sugars (fuel for energy) are in short supply, hydrolysis enzymes break the bonds between starch’s monomers to release glucose subunits. Some common Polysaccharides and their characteristics are given below:
Monosaccharides are the building blocks of more complex carbohydrates. For example, two monosaccharides can bond to form a disaccharide (two sugar unit).
Examples: Sucrose (glucose+fructose) (Table Sugar)
Lactose (glucose+galactose) (Milk Sugar)
Maltose (glucose+glucose) (figure Right)
Before disaccharides can be used by organisms, they must be broken down into their monosaccharide units. The disaccharides have the molecular formula C12H22O11.
A disaccharide is formed upon the formation of a glycosidic linkage (a type of bond) between monosaccharides. This glycosidic linkage forms via a dehydration synthesis reaction.
The “complex” carbohydrates, or polysaccharides, are straight or branched chains of many sugar monomers, often hundreds or thousands of them. There may be one type or many types of monomers in a polysaccharide (many sugar units). Most macromolecular carbohydrates are polysaccharides. Polysaccharides typically serve as (i) carbon and energy storage molecules (starch, glycogen) or (ii) as structural material (e.g., in plants, insects, and fungi).
Most plants make much more glucose than they can use. The excess is stored as starch inside cells that make up roots, stems, and leaves. Some starches are made of thousands of monosaccharide (glucose) units.
Potatoes, beans, and grains such as rice, corn, and wheat are examples of plants that store large quantities of starch. When sugars (fuel for energy) are in short supply, hydrolysis enzymes break the bonds between starch’s monomers to release glucose subunits. Some common Polysaccharides and their characteristics are given below:
Functions of Carbohydrates
- Providing energy and regulation of blood glucose
- Sparing the use of proteins for energy
- Breakdown of fatty acids and preventing ketosis
- Biological recognition processes
- Flavor and Sweeteners
- Dietary fiber, which is also a form of carbohydrate, is essential for the elimination of waste materials and toxins from the body
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