Carbohydrates are the important organic molecules in living organisms. They form the principle source of energy for the body. They constitute the basic component of our food. They are produced by the plants by photosynthesis. It is found that about 80% of the dry weight of the plant body is made up of carbohydrates.
Carbohydrates are formed of carbon, oxygen and hydrogen. The term carbohydrates are derived from hydrated carbon. The proportion of hydrogen and oxygen is same as in water. All carbohydrates are made up of carbon, hydrogen and oxygen in the proportion 1:2:1. The general formula for carbohydrates is CnH2nOn, where n represents the number of components concerned.They are generally known as saccharides or compounds containing sugar. Carbohydrates include a number of micro and macro molecules. Important micromolecules are monosaccharides and oligo saccharides
Definition: Carbohydrates are substances which are either polyhydroxy aldehydes or ketones or are substances that yield polyhydroxy aldehydes or ketones on hydrolysis, e.g. glucose is polyhydroxy aldehyde and fructose a polyhydroxy ketone.
Functions of small carbohydrates
- Monosaccharides have an important role in the metabolism. Trioses, pentoses and heptoses are the intermediate compounds in the photosynthetic pathways.
- During respiration glucose is broken down to release energy.
- Lactose is synthesised in mammary glands from glucose and galactose.
- Fats and amino acids can be synthesised from glucose
- Ribose and deoxyribose are the components of nucleic acid.
- Monosaccharide get polymerised to structural and functional compound carbohydrates called oligosaccharides or polysaccharides e.g, oligosaccharides of cell membranes; structural polysaccharides like cellulose of cell walls; food storage polysaccharides like starch and glycogen.Isomers: Compounds with the same chemical formula are called isomers.
Biochemistry Study Materials
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They are the simplest sugars and cannot be hydrolysed into simpler compounds. The general formula is cnh2non. They are further classified on the basis of number of carbon atoms present in molecule.
Triose (contain 3 carbon atoms)
- Example: Glyceraldehyde and dihydroxy acetone
Tetrose(contain 4 carbon atoms)
- Example: Erythose and Threose
Pentose (contain 5 carbon atoms)
- Example: Ribose, Ribulose, Deoxyribose, Arbinose, Xylose, and Xylulose.
Hexose (contain 6 carbon atoms)
- Example: Glucose, Fructose,Mannose and Galactose
Heptose (contain 7 carbon atoms)
- Example: Sedoheptulose
Biologically important mono saccharides
Yield two molecules monosaccharides on hydrolysis. The general formula of a disaccharide is C12H22O11. They are mostly sugars and may be reducing or non reducing.
Non -reducing sugars:
- Sucrose (Table sugar) consists of glucose and fructose
- Trehalose consists of glucose and glucose.
- Maltose (Malt sugar)consists of glucose and glucose
- Lactose (Milk sugar) consists of glucose and galactose
- Meliobiose consists of glucose and galactose
- Cellobiose consists of glucose and glucose
- Gentiobiose consists of glucose and glucose
Biologically important Disaccharides
On hydrolysis they yield many monosaccharides and are non sugars. The general formula is (C6H10O5)x.
Include the following non-sugars
- Pentosans: Arban and Xylan
- Hexosans: They are further classified into four.
- Glucosans: Starch, Cellulose and Glycogen
- Fructosans:Inulin, Graminin, Synanthrin
- Mannans: Mannane, Mannocellulose
- Galactans: Galactane, Paragalactane
- Pectic compounds: Pectic acid, Pectin and Protopectin
- Amino hexanes
Those substances which are generally made up of aminosugars or their derivatives and uronic acid units, are known as mucopolysaccharides.
Example: Heparin,Hyaluronic acid, Chondroitin sulphates
Are polymers of mono saccharide containing two to six molecules of simple sugars. Disaccharides are most abundant oligosaccharides found in cells.
Sagar Bhakare on October 05, 2017:
Deena (author) from India on January 01, 2012:
Thanks for the visit & Comment
Dee aka Nonna on November 28, 2011:
I have, indeed, learn a great deal reading this excellent hub. I love all the wrong carbs, but I don't very often indulge. When I eat the wrong one I tend to be very tired. Since I have a very busy life I have to keep my energy level up. Thank you for sharing.