Carbohydrates: Structure, Types, and Classification and functions

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Carbohydrates are a fundamental class of biomolecules composed of carbon, hydrogen, and oxygen atoms. They serve as a primary source of energy and play critical roles in various physiological processes. Carbohydrates are classified based on their size, structure, and function into various types, such as monosaccharides, disaccharides, and polysaccharides.

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1. Monosaccharides:

Monosaccharides are the simplest carbohydrates, consisting of a single sugar molecule. They serve as the building blocks for more complex carbohydrates. Monosaccharides are further categorized based on the number of carbon atoms they contain:

Trioses: Monosaccharides with three carbon atoms (e.g., glyceraldehyde and dihydroxyacetone).

Tetroses: Monosaccharides with four carbon atoms.

Pentoses: Monosaccharides with five carbon atoms (e.g., ribose and deoxyribose, components of nucleic acids).

Hexoses: Monosaccharides with six carbon atoms (e.g., glucose, fructose, and galactose).

2. Disaccharides

Disaccharides are composed of two monosaccharide units linked by a glycosidic bond, formed through a dehydration reaction. Common disaccharides include:

Sucrose: Comprising glucose and fructose; found in table sugar.

Lactose: Consisting of glucose and galactose; found in milk.

Maltose: Comprising two glucose units; produced during starch digestion.

3. Polysaccharides:

Polysaccharides are complex carbohydrates formed by the linking of numerous monosaccharide units. They function as energy storage molecules and structural components in cells. Polysaccharides can be further classified into:

Starch: A glucose polymer and the primary energy storage form in plants.

Glycogen: Similar to starch but found in animal cells, particularly in the liver and muscles.

Cellulose: Composed of glucose units linked by β-1,4 glycosidic bonds; a major component of plant cell walls.

Chitin: Found in the exoskeletons of arthropods and cell walls of fungi, composed of N-acetylglucosamine units.

Oligosaccharides:

Oligosaccharides are a class of carbohydrates composed of a small number of monosaccharide units, typically 3 to 10 sugar molecules, joined together by glycosidic bonds. They are found in various biological systems, including plants, animals, and microorganisms. Oligosaccharides play important roles in diverse biological processes and are known for their prebiotic and immunomodulatory properties.

Carbohydrate Classification:

Carbohydrates can also be classified based on their structural complexity and function:

Simple Carbohydrates: Comprising monosaccharides and disaccharides; readily absorbed and provide quick energy.

Complex Carbohydrates: Comprising polysaccharides; digested more slowly, providing sustained energy and dietary fiber.

Functions of Carbohydrates:

• Energy Source: Carbohydrates are the body's primary source of energy. Glucose, derived from carbohydrate digestion, is utilized by cells for various metabolic activities, including ATP production.
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• Energy Storage: Carbohydrates are stored as glycogen in animals and as starch in plants. These storage forms provide a readily available source of energy when glucose levels are low.
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• Structural Support: Polysaccharides like cellulose and chitin contribute to the structural integrity of plant cell walls, fungal cell walls, and arthropod exoskeletons.
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• Dietary Fiber: Certain complex carbohydrates, such as cellulose and pectin, are considered dietary fiber. They aid in digestion, prevent constipation, and promote overall gut health.
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• Cell Communication: Carbohydrates on cell surfaces, known as glycoproteins and glycolipids, play a role in cell recognition, immune response, and signaling processes.
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• Nucleic Acid Components:
• Pentose sugars (ribose and deoxyribose) are integral components of RNA and DNA, respectively, playing a critical role in genetic information storage and transmission.

Exercise Questions:

1. Define carbohydrates and explain their elemental composition.

2. Describe the structural difference between monosaccharides and disaccharides, providing examples        of each.

3. Compare and contrast starch and glycogen in terms of their function, location, and overall structure.

4. How does cellulose differ from other polysaccharides in terms of its linkage and function? What role      does it play in plant cells?

5. Discuss the significance of carbohydrates as an energy source in the context of human metabolism.

These exercise questions will test your understanding of carbohydrate structure, types, and functions, allowing you to deepen your knowledge on the topic.

Source.: 

Fig.1- <a href="https://www.freepik.com/free-vector/scientist-looking-molecules-through-magnifier-female-doctor-doing-research-exploring-neurons-using-scientific-algorithms-flat-vector-illustration-neuroscience-concept_28480815.htm#query=molecules&position=48&from_view=search&track=sph">Image by pch.vector</a> on Freepik

Fig. 2- https://biokimicroki.com/carbohydrates-classification-structure-and-functions/