Types of Carbohydrates with examples and important facts

Dear Aspirants,
“Types of carbohydrates” is one of the important topics of general science. Several questions on this topic are asked in various competitive exams. One of the most common questions asked in exams is – “Which is the sweetest sugar in the world”?

Carbohydrates definition

☛ Those biomolecules which consisting of carbon (C), hydrogen (H), and oxygen (O) atoms, usually with a hydrogen-oxygen atom ratio of 2:1, called Carbohydrates.

☛ Carbohydrates are also called Saccharides which means Sugar.

Sources of Carbohydrates

Plant Sources of carbohydrate
☛ Rice, Wheat, Sugarcane, Bajra, Potato, Vegetables, Mango, Banana, Maize, Carrot, Apple, Lentils, Grapes, etc.

Animal Sources of carbohydrate
☛ Stored glycogen in the liver and muscle of Goat.

Chemical Structure of Carbohydrates

☛ Consists of Carbon, Hydrogen, and Oxygen.

☛ Hydrogen and Oxygen ratio 2: 1 like Water.

☞ General formula C_n(H2O)_n.

Nutritional Significance of Carbohydrates

☛ The main function of carbohydrates is to provide energy to our bodies.
☛ For an adult, 3000 Kcal of energy is needed every day.
☛ Among 3000 Kcal of energy,47% or 1400 Kcal of energy came from carbohydrates.
☛ Daily Carbohydrate requirements – 405 gm.
☛ The calorific value of Carbohydrates is – 4.1 K-cal/g

The biological significance of carbohydrates

☛ Carbohydrates play a significant role in a living organism. The role of carbohydrates in living organisms is described in the following points:

Storage Role

☛ Carbohydrates in plants and animals serve as a store of metabolic fuel.

☛ For example, starch is present in plants and glycogen is present as a storage form in animals.

☛ The storage form, which is starch in plants and glycogen in animals, is broken down into glucose units to provide needed energy.

Structural Role

☛ Carbohydrates such as cellulose, hemicellulose, and lignin provide mechanical and protective functions to plant cell walls.

☛ It gives a definite shape to plant cells and the outer exoskeleton of insects and crustaceans, which is composed of chitin.

☛ Glycosaminoglycans like hyaluronic acid, heparin, chondroitin sulfate, and dermatan sulfate are a part of an extracellular matrix that plays a structural role in bacteria and animals only.

☛ It is a unit of acidic sugar and amino sugar.

Communication Role

☛ Carbohydrates are covalently bound to proteins or lipids to form glycoproteins or glycolipids. They act as hormones and enzymes respectively.

☛ Glycoproteins act as a TSH (Thyroid-stimulating hormone) and erythropoietin hormone.

☛ It also acts as an enzyme (phosphatase, lipase, pepsinogen), receptor, and integral membrane protein.

☛ And glycolipids function as membrane proteins, enzymes, secretory proteins, and immunoglobulins.

Types of carbohydrate

☛ Carbohydrates are classified into two broad categories, namely simple carbohydrates, and complex carbohydrates

☛ Simple carbohydrates are called monosaccharides. Complex carbohydrates are of two types, namely oligosaccharides and polysaccharides.

Monosaccharides

☛ Greek word monos means — single and sacchar means – sugar.
☛ Monosaccharides are also called simple sugars.
☛ It is the simplest form of sugar and the most basic units (monomers) of carbohydrates.
☛ The general formula is C_nH_2nO_n

☛ Monosaccharide carbohydrates are those carbohydrates that cannot be hydrolyzed further to give simpler units of polyhydroxy aldehyde or ketone.

☛ If a monosaccharide contains an aldehyde group (-CHO) then it is called aldose and on the other hand, if it contains a keto group then it is called a ketose (C=O).

☛ Monosaccharides are the building blocks of disaccharides (such as sucrose and lactose) and polysaccharides (such as cellulose and starch).

☛ Examples of monosaccharides :
• Glucose (dextrose)
• Fructose (levulose)
• Galactose.

Structure of Carbohydrates – Glucose

☛ The naturally occurring form of glucose is d-glucose, while l-glucose is generated synthetically in relatively small amounts and is less biologically active.

☛ Glucose is a monosaccharide containing six carbon atoms and an aldehyde group (-CHO) and is therefore an aldohexose.

☛ The glucose molecule can exist in an open-chain (acyclic) as well as ring (cyclic) form.

Facts about Glucose

☛ Glucose is a simple sugar with the molecular formula C6H12O6. It is the most abundant monosaccharide in the world.

☛ It is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy from sunlight.

☛ In plants Glucose is used to make cellulose in cell walls.
☛ In energy metabolism, glucose is the most important source of energy in all organisms.

☛ Glucose is stored as a polymer for metabolism, mainly as starch and amylopectin in plants, and as glycogen in animals.

☛ In animals, glucose is released from the breakdown of glycogen in a process known as glycogenolysis.

☛ Glucose circulates in the blood of animals as blood sugar. It is naturally occurring and is found in its free state in fruits and other parts of plants.

Structure of Carbohydrates – Fructose

☛ The molecular formula of fructose is C6H12O6.
☛ It is an important ketohexose.
☛ It has a Ketone(-CO) functional group.

Facts about Fructose

☛ Fructose was discovered in 1847 by the French chemist Augustin-Pierre Dubrunfaut and the name “fructose” was coined in 1857 by the English chemist William Allen Miller.

☛ Fructose or fruit sugar is a ketonic simple sugar and is the sweetest sugar in the world.
☛ It is one of three dietary monosaccharides, along with glucose and galactose.

☛ The liver converts both fructose and galactose into glucose.
☛ Pure, dry fructose is the most water-soluble of all sugars.

☛ Commercially, fructose is obtained from sugarcane, sugar beet, and corn.
☛ High-fructose corn syrup is a mixture of the monosaccharides glucose and fructose.
☛ Sucrose is a compound with a molecule of glucose covalently linked to a molecule of fructose.

Oligosaccharide

☛ An oligosaccharide is a polymer of saccharides containing two to ten monosaccharides

☛ Most of the Oligosaccharides in the cell are found on the cell membrane. These are present at the outer side of the cell.

☛ Classified into 3 groups: Disaccharide, Trisaccharide, and Tetrasaccharide.

☛ Disaccharide

☛ A disaccharide is a sugar formed when two monosaccharides are joined by glycosidic linkages. Like monosaccharides, disaccharides are simple sugars soluble in water.

☛ Most common examples of Disaccharide: Lactose, Sucrose, Maltose
☛ General formula of – C_n(H₂O)_n-1

✓ Sucrose = Glucose + Fructose
✓ Maltose = Glucose + Glucose   
✓ Lactose = Glucose + Galactose

☛ Trisaccharide

☛ Three monosaccharides join together
☛ It is found in the Sugarbeet.

☛ Examples of Trisaccharides – Raffinose, Robinose, and Manotriose.

✓ Raffinose = Glucose + Galactose + Fructose

☛ Tetrasaccharide
• Example – Stachyose, Scorodose

Polysaccharides

☛ Polysaccharides consist of more than 10 monosaccharide units, that are joined together by glycosidic linkages.

☛ It is a polymer of α glucose and consists of two components-Amylose and Amylopectin.

☛ During the formation of Polysaccharides the water molecules are released:
n(C₆H₁₂O₆) (C₆H₁₀O₅)_n + nH₂O

☛ General formula of Polysaccharide – (C₆H₁₀O₅)_n

☛ Examples of Polysaccharides – Starch, Dextrins, Inulin, Cellulose

Types of Polysaccharides

Homopolysaccharides
☛ Made up of a single kind of monosaccharides.
☛ Examples: Starch, Glycogen, Cellulose, Chitin, Inulin

☛ Starch is the main storage polysaccharide in plants. It is composed of α-D- glucose units.

☛ Cellulose is also one of the polysaccharides that are mostly found in plants. It is composed of β-D- glucose units joined by a glycosidic linkage between C1 of one glucose unit and C4 of the next glucose unit.

Heteropolysaccharides
☛ Made up of more than one type of Monosaccharides.
☛ Examples: Pectin, Peptidoglycan, Agar-agar

Frequently Asked Questions (FAQ)