Introduction
Carbohydrates are also known as carbs, which are molecules made of sugar. Carbohydrates are one of three main nutrients found in foods and drinks along with proteins and fats.
Carbohydrates are broken down into glucose by our body. Glucose, or the blood sugar, is our body’s main source of energy for your body’s cells, tissues, and organs. Glucose can be immediately used or stored in the liver and muscles for use afterwards.
Common foods with carbohydrates include:
- Bread, noodles, pasta, crackers, cereals which are generally made of grain and rice
- Fruits, like apples, bananas, berries, mangoes, melons, and oranges
- Dairy products, for example milk and yoghurt
- Dried beans, lentils, and peas which are rich in fibre
Structure of Carbohydrate
Carbohydrates can be represented by the chemical formula (CH2O)n, where n is the number of carbons present in the molecule. In simpler words, the ratio of carbon to hydrogen to oxygen is 1:2:1 in carbohydrate molecules, which means a molecule of carbohydrate is composed of one atom of carbon and oxygen and two atoms of hydrogen in a given proportion. This formula also explains the origin of the term carbohydrate where the components are carbon (carbo) and the components of water (hydrate).
They are organic compounds arranged in the form of aldehydes or ketones with multiple hydroxyl groups coming from the carbon chain.
The carbohydrates can be structurally represented in any of the three forms:
Open chain structure: It is the long and straight-chain form of carbohydrates.
Hemi-acetal structure: Under this structure the first carbon of the glucose condenses with the -OH group of the fifth carbon to form a ring structure.
Haworth structure: It is the presence of the pyranose ring structure, which is a chemical structure that has five carbon atoms and one oxygen atom.
Types of Carbohydrates
Carbohydrates are mainly of three types as follows:
Monosaccharides
The simple carbohydrates are called simple sugars or monosaccharides. They are the monomers or simply the building blocks for the synthesis of complex carbohydrates. Monosaccharides are classified on the basis of the number of carbons atoms present in the molecule for example, triose (with three carbon atoms), tetrose (with four carbon atoms), pentose (with five carbon atoms) and hexose (with six carbon atoms).
Monosaccharides which have four or more carbon atoms are seen more even when they adopt ring structures. These ring structures are results of a chemical reaction between functional groups on opposite ends of the flexible carbon chain of sugar, namely the carbonyl group and a relatively distant hydroxyl group. For example, glucose forms a six-structured ring.
Oligosaccharides
Obtained by joining three to six units of simple sugars or monosaccharides, oligosaccharides are essentially carbohydrates in their purest form. In rare instances, however, as many as ten units of sugar have been observed to combine to form an Oligosaccharide. They are either formed by the combination of monosaccharide molecules or they are formed by the breaking down of complex sugars known as polysaccharides, depending on how they are formed. Only a small number of oligosaccharides are found in nature, and they are found in plants. To name a few examples: Raffinose is composed of three monosaccharide molecules, melibiose, gentianose, and fructose, which combine to form the compound. One oligosaccharide can be obtained from arthropod blood and from a few plants, the most notable of which is Maltotriose, which is composed of three glucose molecules.
Polysaccharides
A long chain of monosaccharides linked by glycosidic bonds is known as a polysaccharide as poly means many. The chain may be branched or unbranched, and it may contain various types of monosaccharides. The molecular weight of a polysaccharide may be 100,000 daltons or more depending on the number of monomers attached together to make a polysaccharide. Starch, glycogen, cellulose, and chitin are some simple examples of polysaccharides.
Starch stored in the form of complex sugars in plants is made up of a mixture of amylose and amylopectin that are polymers of glucose. Plants are able to produce glucose, and the excess glucose after the immediate energy needs of the plants, is stored as starch in different plant parts, including roots and seeds.
Functions of Carbohydrate
The functions of carbohydrates in the human body are discussed below:
Energy Production: The primary role of carbohydrates is to provide energy to all cells in the body. Many cells prefer glucose as a source of energy in comparison to other compounds like fatty acids. Some cells, such as red blood cells, can only produce using cellular energy from glucose.
In the breakdown of glucose, the first step is called glycolysis, which occurs in a complex series of ten-reaction steps. The second stage of glucose breakdown occurs in the mitochondria which is the powerhouse of the cells. One carbon atom and two oxygen atoms are removed producing more energy. The energy from these carbon bonds is taken to another part of the mitochondria which makes the cellular energy use the energy in the available form.
Energy Storage: When the body has sufficient energy to support its functions, the excess glucose in the body is stored as glycogen, the majority of which is stored in the muscle and liver. A molecule of glycogen may contain over fifty thousand single glucose units and is highly branched, allowing for the speedy distribution of glucose when it is needed to make for the cells.
Building Macromolecules: Majority of the absorbed glucose is used to make energy, some glucose is altered into ribose and deoxyribose, which are important building blocks of important macromolecules, such as RNA, DNA, and ATP.
Glucose is additionally used to make the molecule NADPH, which is important for protection against oxidative stress and is utilized in many other chemical reactions in the body. If all of the energy is used in building needs of the body, excess glucose can be used to make fat.
Sparing Protein: When there is not sufficient glucose to meet the body’s needs, glucose is released from amino acids. As molecules of amino acids cannot be stored, this process requires the destruction of proteins, primarily from tissues of the muscles. The presence of sufficient glucose basically excludes the breakdown of proteins needed by the body from being used to make glucose.
Lipid Metabolism: As glucose level of the blood rises, the use of lipids as an energy source is inhibited. Therefore, glucose excessively has a ‘fat-sparing’ effect. It is because an increase in glucose level of blood enhances release of the hormone insulin, which orders cells to use glucose instead of lipids for production of energy.
Sufficient glucose levels in the blood also prevent the development of ketosis. Ketosis is a metabolic condition which results from an elevation of ketone bodies in the blood. Ketone bodies are an alternative source of energy that cells can use when there is insufficient glucose supply such as during fasting.
Conclusion
We can conclude from the above discussion that carbohydrates are one of three main nutrients found in foods and drinks along with proteins and fats. Fruits, like apples, bananas, berries, mangoes, melons, and oranges. The structure of the carbs is also discussed in the article. The function of carbohydrates like energy production, energy storage, etc. are also elaborated. The three types of carbohydrates and their importance is also discussed.