TABLE OF CONTENTS The final major category of biological molecules that we will discuss is carbohydrates. Carbohydrates are the ultimate source (either directly or indirectly) of most of our food and makes up most of the organic matter on earth. Carbohydrates are important because they serve several roles to all forms of life. These include serving as an energy store and an intermediate in metabolism. They also are important as the sugars in DNA and RNA, where it is apparent that their size and flexibility is critical to the expression of genetic information. A class of carbohydrates, polysaccharides, is a structural element in cell walls of bacteria and plants and in the exoskeleton of insects and Crustacea. Finally, many carbohydrates are covalently linked to proteins and lipids.
The ubiquitous nature of carbohydrates in life will be discussed in the next few paragraphs. We will then discuss the chemistry of these materials and some of their biological functions.
D-glucose is a carbohydrate formed in the leaves of plants from carbon dioxide, CO 2, and water, H 2O, via the process of photosynthesis that utilizes energy from light and the catalyst chlorophyll. D-glucose is used for a variety of purposes. For example, thousands of D-glucose molecules may be combined into larger molecules called cellulose, which provides support for the plant. D-glucose can be combined in a different way to form large molecules of starch that is stored in seeds to serve as food for sprouting plants. Starches are polymers that...
