Carbohydrates are a class of biomolecules that are composed of simple sugars, such as glucose and fructose, linked together through glycosidic bonds. They play important roles in energy storage and transport, as well as in structural support and cell-cell recognition.

Types of carbohydrates

There are three main types of carbohydrates: monosaccharides, disaccharides, and polysaccharides.

Monosaccharides 

Monosaccharides are the simplest form of carbohydrates, and they cannot be hydrolyzed into smaller sugars. They are also called simple sugars. Examples of monosaccharides include glucose, fructose, and galactose. These sugars have the molecular formula (CH2O)n, where n is typically between 3 and 7. They have an aldehyde or ketone functional group, which allows them to participate in a wide range of chemical reactions.

For example, the structure of glucose:

H – C – H

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H – C – O – H

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H – C – H

Glucose is a six-carbon sugar with an aldehyde functional group (-CHO) on the first carbon. It is a hexose sugar.

Similarly, this is the structure of fructose:

H – C – H

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H – C – O – H

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H – C – O – H

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H – C – H

Fructose is a six-carbon sugar with a ketone functional group (-CO-) on the second carbon. It is also a hexose sugar.

Disaccharides

Disaccharides are formed by the condensation of two monosaccharides, resulting in the removal of a molecule of water. Examples of disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose). They are also known as double sugars. They are easily hydrolyzed by enzymes such as sucrase, lactase, and maltase, which split them into their component monosaccharides.

Sucrose, a disaccharide composed of glucose and fructose, can be represented as:

Glucose: H – C – H | | H – C – H

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H – C – O – H | | H – C – H

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H – C – H

Fructose: H – C – H | | H – C – H

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H – C – O – H | | H – C – O – H

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H – C – H

Sucrose is formed by a glycosidic linkage between the anomeric carbon of glucose and the C-4 carbon of fructose.

Polysaccharides

Polysaccharides are long chains of monosaccharides linked together. They serve as a storage form of energy, structural support, and cell-cell recognition. Examples of polysaccharides include glycogen, cellulose, and chitin.

Glycogen is a highly branched polymer of glucose molecules, with the glucose units linked together by alpha-1,4 glycosidic bonds. It is made up of chains of glucose units, with branches being formed by alpha-1,6 glycosidic bonds.

Glycogen is the main storage form of glucose in animals. It is present in the liver and muscles. Enzyme glycogen phosphorylase hydrolyzes glycogen into glucose during the energy requirement of body.

Cellulose is a linear polymer of glucose molecules, with the glucose units linked together by beta-1,4 glycosidic bonds. It is an important structural component of plant cell walls.

Cellulose is the main structural component of plant cell walls. It is indigestible by humans, but it is an important source of dietary fiber.

Chitin is a linear polymer of N-acetylglucosamine Chitin is a linear polymer of N-acetylglucosamine molecules, with the N-acetylglucosamine units linked together by beta-1,4 glycosidic bonds. 

It is the main component of the exoskeleton of arthropods and the cell walls of fungi.

Conclusion

Carbohydrates are a diverse class of biomolecules that play important roles in energy storage and transport, as well as in structural support and cell-cell recognition. They are composed of simple sugars, such as glucose and fructose, linked together through glycosidic bonds. Monosaccharides, disaccharides, and polysaccharides are the three main types of carbohydrates, each with specific functions and properties. Understanding the structures and properties of carbohydrates is crucial for understanding their roles in the biochemistry of living organisms.