[Chemistry Class Notes] on Structure and Classification of Carbohydrates Pdf for Exam

Carbohydrates are a group of organic compounds that occur in living tissues and foods in the form of sugars, cellulose, and starch. The general formula of carbohydrates is [CH_{2}O_{n}]. Just as in water, the ratio of oxygen and hydrogen is fixed in carbohydrates, which is 2:1. It generally breaks down to release energy in humans and animals. Today, we are going to learn about the classification of carbohydrates and their structures.

Carbohydrates Classification

Given below is the classification of carbohydrates in biochemistry.

Types of Carbohydrates – Simple Carbohydrates

The basic type of carbohydrates is simple carbohydrates that are found in natural sugars present in fruits, vegetables, milk, and honey. These carbohydrates are much simpler to study since they have a less complex structure.

Simple carbohydrates consist of only units of monosaccharides, which is why they are the smallest and simplest of all the other types of carbohydrates. Their smaller size plays a vital role in metabolism and digestion in the gastrointestinal tract.

Types of Carbohydrates – Complex Carbohydrates

Complex carbohydrates are an essential source of energy for our body. They give us the sustained fuel that our body needs for carrying out day-to-day activities, for working out, and for even taking rest. Complex carbohydrates often comprise different units of monosaccharides bound together and provide us with long-lasting energy. The complex carbohydrates are classified depending on their hydrolysis behavior. They are divided into three groups as follows.

1. Monosaccharides

2. Disaccharides

3. Polysaccharides

Monosaccharides

Monosaccharides are carbohydrates that cannot be hydrolyzed further for giving simpler units of either a polyhydroxy aldehyde or a ketone. If a monosaccharide consists of an aldehyde group, it is referred to as aldose and if it consists of a keto group then it is referred to as a ketose.

Disaccharides

After the process of hydrolysis, disaccharides tend to yield either two molecules of the same or the different monosaccharides.

1. Two units of monosaccharide are joined by an oxide linkage that is formed when there is the loss of water molecule, and this linkage is referred to as glycosidic linkage.

2. Sucrose is amongst the most common disaccharides that give both glucose and fructose on hydrolysis.

3. Maltose and lactose, often referred to as milk sugar, are also the two kinds of important disaccharides.

4. Maltose contains two α-D-glucose whereas lactose consists of two β-D-glucose that are connected through an oxide bond.

Polysaccharides

1. Polysaccharides consist of longer monosaccharide units that are joined together by glycosidic bonds.

2. Most of these polysaccharides act as storage for food, such as starch. Starch is known to be an important storage polysaccharide in plants.

3. Starch is a polymer of α glucose and has two components, that are amylose and amylopectin.

4. Cellulose is also an essential polysaccharide that is found mostly in plants.

5. It comprises β-D- glucose units that are joined by a glycosidic bond between the C1 of one glucose unit and the C4 of another glucose unit.

Structure of Carbohydrates

Carbohydrates have traditionally been characterized as compounds having the empirical formula [Cn(H_{2}O)m]. Glucose, fructose, and sucrose are popular sugars that suit this formula, however, currently, a carbohydrate is defined as a polyhydroxy aldehyde or polyhydroxy ketone with the traditional formula, a molecule closely similar to it, or oligomers or polymers of such molecules. Because they are water-soluble and difficult to crystallise, they need a different set of abilities to manipulate than traditional “natural products” like terpenes, steroids, and alkaloids.

A “monosaccharide” is a carbohydrate derivative with a single carbon chain; “disaccharide” and “trisaccharide” are compounds with two or three monosaccharide units linked together by acetal or ketal linkages. Larger aggregates with “a few” and “many” monosaccharide units are referred to as “oligosaccharide” and “polysaccharide,” respectively. The divide between “few” and “many” appears to be drawn at roughly 10 units in current use.

By the middle of the nineteenth century, chemists in Europe, particularly in Germany, had discovered a variety of relatively pure carbohydrates such as sucrose, cotton cellulose, starch, glucose, fructose, mannose, and lactose. Emil Fischer produced phenylhydrazine for his University of Munich thesis in 1878. He also found in 1884 that carbohydrates produced crystalline phenylosazone when two phenyl hydrazines interacted with the aldehyde group and the carbon next to it.

Structure of Carbohydrates – Glucose

Glucose is amongst the most important monosaccharides. The two commonly used methods to prepare glucose are as follows.

1. From Sucrose: When sucrose is boiled with dilute acid in an alcohol solution, glucose and fructose are obtained.

2. From Starch: Glucose can also be obtained by the hydrolysis of starch and boiling it with dilute sulphuric acid, at a temperature of 393K, under high pressure.

Glucose is also known as dextrose and aldohexose and is plentiful on earth.

Structure of Carbohydrates – Fructose

Fructose is an essential ketohexose having a molecular formula [C_{6}H_{12}O_{6}]. It consists of a ketone functional group situated at carbon number 2 and contains six carbon atoms in the form of a straight chain. The ring member of fructose is analogous to the compound called Furan and is therefore termed furanose. The cyclic structure of fructose is as follows:

Conclusion

We are all surrounded Carbohydrates are a group of organic compounds that occur in living tissues and foods. The general formula of carbohydrates is [CH_{2}O_{n}]. Just as in water, the ratio of oxygen and hydrogen is fixed in carbohydrates, which is 2:1.