Concepts and formula to Remember
No. of carbon in carbohydrates
| Classification | Number of Carbon Atoms | Examples |
|---|---|---|
| Trioses | 3 | Glyceraldehyde |
| Tetroses | 4 | Erythrose, Threose |
| Pentoses | 5 | Ribose, Deoxyribose |
| Hexoses | 6 | Glucose, Fructose, Galactose |
| Heptoses | 7 | Sedoheptulose, Manheptulose |
Difference between starch and cellulose
| Characteristic | Cellulose | Starch |
|---|---|---|
| Structure | Polysaccharide composed of glucose units linked by β-1,4-glycosidic bonds | Polysaccharide composed of glucose units linked by α-1,4-glycosidic bonds (amylose) with occasional α-1,6 branch points (amylopectin) |
| Function | Provides structural support in plant cell walls | Serves as an energy storage molecule in plants, storing excess glucose |
| Digestibility | Not digestible by most animals due to β-1,4-linkages | Readily digestible by humans and many animals, broken down into glucose for energy |
| Dietary Fiber | Important dietary fiber for human nutrition, aids in digestion and bowel regularity | Provides a source of carbohydrates in the human diet |
| Source | Found in plant cell walls, primarily in cellulose-rich plant materials | Found in grains, legumes, tubers, and other plant-based foods |
| Molecular Structure | Linear, unbranched structure | Can exist in two forms: amylose (unbranched) and amylopectin (branched) |
Cellulose: Cellulose is a complex carbohydrate found in the cell walls of plants. It is a polysaccharide made up of glucose units linked together. Cellulose provides structural support to plant cells and gives rigidity to plant tissues. It’s a type of dietary fiber that is indigestible by humans but essential for maintaining digestive health. Cellulose does not form blue colour with Iodine because it does not contain complex helices and hence cannot hold iodine molecules.
Starch: Starch is also a complex carbohydrate composed of glucose units linked together. It serves as a major energy storage molecule in plants, being the primary form of carbohydrate storage in seeds, tubers, and roots. When humans consume starch, digestive enzymes break it down into glucose, which can be used as a source of energy.
Lactose: Lactose is a disaccharide sugar composed of glucose and galactose molecules linked together. It is commonly found in milk and dairy products. Lactose is digested in the small intestine by the enzyme lactase, which breaks it down into its component sugars for absorption. Some individuals have lactose intolerance, which means they lack sufficient lactase enzyme to digest lactose properly, leading to digestive discomfort after consuming dairy products.
