Kinds of Carbohydrate
Carbohydrates are a group of organic compounds composed of carbon, hydrogen and oxygen. The general formula is Cx(H2O)y There are three main groups of carbohydrates; monosaccharides (single sugars), disaccharides (double sugars) and polysaccharides (many sugars). Most carbohydrates are used for storage and release of energy. And also,
some, such as cellulose in plants, are used for structure.
Monosaccharides
There are a number of monosaccharides; glucose, fructose and galactose.
While they all have the same chemical formula, structurally they are very different.
They are showed the different structures. Glucose and Galactose form a six-sided ring (pyranose ring), fructose forms a five-sided ring (furanose ring). Note that it is not always necessary to show all the C
atoms when drawing the ring.
Disaccharides
Monosaccharides can combine together in pairs to make disaccharides. This chemical reaction also releases a water molecule (H2O) and is known as a condensation reaction (joining molecules together) or dehydration reaction(releasing water) (We will study condensation reaction and dehydration reaction next learning, these are really important!)#.
The chemical bond formed between the monosaccharides is said a glycosidic bond.
Also, it is possible, under the correct conditions, to add a molecule of water to a disaccharide and split it into two monosaccharides.
This reaction is known as hydrolysis.
Polysaccharides
In the same way that two monosaccharides can combine to form disaccharides, many monosaccharides can combine by condensation reactions to make polysaccharides.
The number of monosaccharides needed is variable, and the chain produced can be either branched or unbranched.
Polysaccharides are insoluble and unreactive, i.e. stable. So, it can be good for energy storage.
Hydrolysis can be used to break them down into monosaccharides which are soluble (they dissolve) in water, and easier for cells to use for energy.
Starch and Glycogen are examples of storage polysaccharides. In addition, the example of a polysaccharide is Cellulose, used to build cell walls in plants.
Starch
Starch is used by plants to store energy. Plants make starch from excess glucose produced by photosynthesis.
Glycogen
(1,4-α-glycosidic linkages in the glycogen oligomer)
The glycogen is the storage polysaccharide used in animals.
It is stored in the liver and muscles.
Each this molecule is the shape of a sphere and has a protein at its canter.
Cellulose
Many parallel chains with cross-linkages make it very stable and strong.
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Biology in a nutshell