Carbohydrates

Carbohydrates provide fast energy (4 kcal/gram) for the human body. You can find them in sweets and starches. Some forms of complex carbohydrates serve as roughage and as the structural backbone of plant cell walls. Carbohydrates are typically classified according to the number of saccharide (sugar) units they have.

• Monosaccharides are composed of a single sugar unit. They are the simplest kind of carbohydrate. Fructose and glucose are two common monosaccharides. However, while glucose and fructose share the same formula (C₆H₁₂O₆), the placement of the carbon atoms is different. Additionally, the placement of a H and OH group in a molecule of glucose determines whether it is alpha glucose or beta glucose.
  
  
  
  Image by Chernobyl Frog Dissections
  
  
• Dissaccharides are composed of two sugar units. They are formed through dehydration synthesis. An example of a dissacharride is sucrose (formed from fructose and glucose).
  
  
• Polysaccharides are composed of three plus sugar units. Since it is formed from repeating units of another molecule it is called a polymer. There are four main kinds of polysaccharides: starch, glycogen, cellulose, and chitin. Starch is the storage form of sugar in plants. It is made of amylose and amylopectin -- each thousands of glucose units in length. Glycogen is the storage form of sugar in animals. It looks like starch, but with more glucose branches attached. Cellulose is a structural carbohydrate that forms cell walls in plants. It is not digestible by either man or other animals. Chitin is a polysaccharide that contains nitrogen. It is found in the exoskeleton of arthropods and the cell walls of fungi.