Carbohydrates and its Types

We encounter many kinds of carbohydrates in our daily lives from bread to starch in our clothes and even rice. Carbohydrates are organic compounds made up of the elements like carbon, hydrogen and oxygen. The hydrogen and oxygen atoms are present in the same ratio, that is, 2:1.

Carbohydrates mainly come from plants and are a good source of energy for the body. There are three main types of carbohydrates; these are the monosaccharides, disaccharides and polysaccharides. The monosaccharides have a simple chemical composition and therefore known as simple sugars. Examples of them are glucose, fructose and galactose.

Disaccharides are also known as complex sugars as they have complex chemical compositions and maltose, lactose and sucrose are their examples. Polysaccharides are the most chemically complex carbohydrate and its examples include starch and cellulose.

The sugar glucose is one of the simplest form of sugars and has the chemical formula C6H12O6. The generalized formula for carbohydrates is CnH2mOm. In the case of glucose, n=6 and m is also equal to six. But in sucrose, n=12 and m=11 and hence its formula is C12H22O11. There are other substances which are slightly modified carbohydrates, such as the chitin of the arthropod skeleton.

There are many functions of carbohydrates, such as they are a source of energy, they form supporting structures, for example, cellulose cell walls in plants. They are also used to make other organic compounds like amino acids and fats. Nucleic acids like DNA are also formed by carbohydrates as well as lubricants like mucus can also be synthesized. Another fascinating function of carbohydrates is that they are also used to produce the nectar in some flowers.

Types of Sugars

Sugars are sweet crystal like compounds which dissolve easily in water. Two types of sugars can be distinguished;

Monosaccharides

The most common monosaccharides have six carbon atoms, with the general formula C2H12O6. Glucose, fructose and galactose are monosaccharides that differ only in details of the arrangement of the various atoms within the molecule which give them different chemical and biological properties.

Glucose also known as grape sugar is found, at least in small quantities, in all animals. Fructose is commonly present in plants, but absent in animals. Galactose is a component of lactose, and is formed when this is digested.

Disaccharides

Disaccharides are complex in structure because each molecule is make up of two molecules of simple sugars condensed together. The most common types of disaccharides – sucrose, lactose and maltose – have 12 carbon atoms, with the general formula C12H12O11. The difference in the disaccharides are again due to the different atomic arrangements within the molecule.

Sucrose, also known as cane sugar, occurs in sugarcane stems, sweet fruits and certain storage roots, for example, carrots. It consists of a glucose and a fructose molecule combined together. It is not found in mammals.

Lactose, also known as milk sugar is commonly found in the milk, as the name suggests. It is found in milk of all mammals, including human and even in some similar fluids such as pigeon’s ‘milk’. It is formed from glucose and galactose combined together.

Maltose also known as malt sugar is present in malted cereals and sprouting grains. It is formed from the partial digestion of starch and is a combination of two glucose molecules.
As mentioned before, the formation of one molecule of disaccharide requires two molecules of simple sugars. Each of this reaction results in a loss of a water molecule and such a reaction is known as a Condensation Reaction. Condensation is a chemical reaction whereby two simple molecules are joined together to form a larger molecule with the removal of one molecule of water.

On the other hand when a disaccharide is heated with acids or treated it with a suitable enzyme, it breaks down to form monosaccharides. In this reaction water is added and thus this reaction is called hydrolysis. A reaction whereby a water molecule is added on to split up a complex molecule into its component units is known as hydrolysis or a hydrolytic reaction.

A sucrose solution, a disaccharide, can be hydrolysed to form glucose and fructose, two monosaccharides. Similarly, we can hydrolyse lactose to glucose and galactose, using the enzyme lactase, and maltose can be hydrolysed glucose using the enzyme maltase.

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