Glucose is a simple sugar, or monosaccharide, that is produced by plants during photosynthesis. Classified as a carbohydrate, glucose serves as the principal source of fuel for your cells, and it is an essential intermediate or cofactor in many other cellular processes, such as fatty acid synthesis and protein activation. When combined with other monosaccharides or when linked together in repeating units, glucose helps to create more complex sugars. Glucose is used to manufacture glycogen in animals and celluloses, hemicelluloses and starches in plants.
Increasing Complexity
Carbohydrates are categorized according to the number of monosaccharides incorporated into their structures. When two monosaccharides are joined together, they form a disaccharide. For example, glucose can be combined with galactose or fructose to form lactose and sucrose, respectively, and two glucose molecules can be combined to form maltose. Carbohydrates containing three to 20 monosaccharides are called oligosaccharides. You may recognize fructo-oligosaccharides, or FOS, as immune-modulating oligosaccharides. Carbohydrates composed of several dozen to hundreds of monosaccharides are called polysaccharides. Starches are a special class of polysaccharides.
Starch
Starches can be distinguished from other polysaccharides by virtue of their monosaccharide content and their unique structure. According to researchers at Elmhurst College, starches consist solely of repeating glucose units, all of which are joined by a specific chemical bond called an alpha-acetal linkage. Starches are further sub-classified according to their source of manufacture and whether their structures contain any branches. Glycogen is a branched-chain starch produced in the tissues of animals. Amylose and amylopectin are straight-chained and branched-chain starches manufactured by plants.
Nutritional Significance
Because they can be readily broken down and absorbed from your intestine, monosaccharides and disaccharides prompt rapid increases in your blood glucose level. In contrast, starches are more slowly digested, and their absorption is more gradual. Variability in absorption among different carbohydrates is the basis for a rating system called the "glycemic index," which is often used by diabetics and others concerned about blood glucose levels. Carbohydrates that are quickly absorbed into your bloodstream, such as glucose, have a high glycemic index, while unrefined starches and other complex carbohydrates have a lower glycemic index.
Considerations
Glucose is essential for your health. Without sufficient supplies of this important monosaccharide, your cells could not function. However, if too much glucose arrives too quickly in your bloodstream following a meal, your body has difficulty processing it. In his book "Staying Healthy With Nutrition," Dr. Elson Haas states that the consumption of high glycemic-index foods -- cookies, cakes and candies -- contributes to insulin resistance and other metabolic problems that increase your risk for diabetes, obesity and heart disease. Complex carbohydrates, such as unrefined starches, furnish the glucose you need in a much healthier form.
References
- "Staying Healthy With Nutrition: Carbohydrate Requirements"; Elson M. Haas, M.D.; 2006
- Elmhurst College: Virtual Chembook -- Starch
