Carbohydrates are probably the most abundant and widespread organic substances in nature and they are essential constituents of all living things. Carbohydrates are formed by green plants from carbon dioxide and water during the process of photosynthesis. Carbohydrates serve as energy sources and as essential structural components in organisms; in addition, part of the structure of nucleic acids, which contain genetic information, consists of carbohydrates.

What are carbohydrates?

A carbohydrate is an organic compound such as sugar or starch and is used to store energy. Like most organic compounds, carbohydrates are built of small, repeating units that form bonds with each other to make a larger molecule. In the case of carbohydrates, the small repeating units are called monosaccharides. The general formula for carbohydrates is Cn (H2O) n.

Sources of carbohydrates:

There are both healthy and unhealthy sources of carbohydrates.

• The healthiest sources of carbohydrates—unprocessed or minimally processed whole grains, vegetables, fruits, and beans—promote good health by delivering vitamins, minerals, fiber, and a host of important phytonutrients.
• Unhealthier sources of carbohydrates include white bread, pastries, sodas, and other highly processed or refined foods.  These items contain easily digested carbohydrates that may contribute to weight gain, interfere with weight loss, and promote diabetes and heart disease.

Types of carbohydrates:

Carbohydrates are among the most abundant compounds on earth. They are two main types of carbohydrates, simple and complex. It is based on its chemical structure.

 Simple carbohydrates are made up of just one or two sugar units, whereas complex carbohydrates are made up of many sugar units.

Simple carbohydrates are further divided into three categories. These are as follows.

Monosaccharides: The word monosaccharide is derived from mono, meaning “one”, and saccharide, meaning “sugar”. The common monosaccharides are glucose, fructose, and galactose. These are also called simple sugars, any of the basic compounds that serve as the building blocks of carbohydrates. Monosaccharides include aldoses, ketoses, and their derivatives.

• Fructose: Fructose is a structural isomer of glucose, meaning it has the same chemical formula but a completely different three-dimensional structure. The main difference is that fructose is a ketone in its linear form while glucose is an aldehyde.

• Glucose: Is the simple sugar with the molecular formula C6H12O6. Is the main type of sugar in the blood and is the major source of energy for the body cells.

• Galactose: Galactose is nearly identical to glucose in structure except for one hydroxyl group on carbon atom number four of the six-sided sugar. Since it differs in only one position about all six asymmetric centers in the linear form of the sugar. 

Disaccharides: Disaccharides, meaning “two sugars”, are commonly found in nature as sucrose, lactose, and maltose. They are formed by a condensation reaction where one molecule of water condenses or is released during the joining of two monosaccharides. The type of bond that is formed between the two sugars is called a glycosidic bond.

Common examples are sucrose, lactose, and maltose:

• Sucrose: Sucrose is a type of sugar made up of one molecule of glucose and one molecule of fructose joined together. It is a disaccharide a molecule composed of two monosaccharides glucose and fructose.

• Lactose: Lactose is a disaccharide formed through the condensation of glucose and galactose. The bond formed between the two monosaccharides is called a beta glycosidic bond.

• Maltose: Maltose is the final disaccharide and consists of two glucose molecules joined by an alpha glycosidic bond. Maltose is an interesting compound because of its use in alcohol production. Through a process called fermentation, glucose, maltose, and other sugars are converted to ethanol by yeast cells in the absence of oxygen.

Complex carbohydrates: complex carbohydrates are made up of sugar molecules that are joined together in long, complex chains. Complex carbohydrates are found in foods such as peas, beans, whole grains, and vegetables. Both simple and complex carbohydrates are turned into glucose in the body and are used as energy.

Polysaccharides: polysaccharides are the most abundant carbohydrate found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate reacts with water using amylase enzymes as the catalyst, which produces constituent sugars.

Main functions of carbohydrates:

Carbohydrates are the body’s primary energy providers. The important functions of carbohydrates are listed below.

• Providing energy and regulation of blood glucose
• Sparing the use of proteins for energy
• Breakdown of fatty acids and preventing ketosis
• Biological recognition processes
• Flavor and Sweeteners
• Dietary fiber.
• They are also important in the diet due to specific functions they perform in the human body such as eliminating or minimizing ketosis, breakdown of body protein, loss of cations, and dehydration.
• In addition, carbohydrates are essential because they are precursors to carbohydrate derivatives that are actively involved in human metabolic processes. 
• Carbohydrates serve as the primary energy source. 
• Functions of carbohydrate systems in the molecular mechanisms responsible for the important aspects of living activity.
• They are essential for the oxidation of fats.
• They exert a sparing action on protons.
• They provide the carbon skeleton for the synthesis of some nonessential amino acids.

Conclusion:

 Carbohydrates are organic compounds. Carbohydrates constitute a group of chemically defined substances with a range of physical and physiological properties and health benefits for consumers. Their main function is to provide energy, but they also play an important role in the structure and function of cells, tissues, and organs.