Chapter 5.2 Summary

A carbohydrate is an organic compund made up of sugar molecules. Sugars contain the elements carbon, hydrogen, and oxygen in the ratio of 1 carbon: 2 hydrogen: 1 oxygen. Simple sugars contain monosaccharides. Glucose exists in straight-chain and right-shaped forms. Sugar molecules are the main fuel supply for cellular work. Cells break down glucose molecules and extract their stored energy. Using the dehydration reaction, cells construct a disaccharide. The most common disaccharide is sucrose. It consists of a glucose molecule linked to a fructose molecule. Long polymer chains made up of simple sugar monomers are called polysaccharides. Starch is a polysaccharide found in plant cell. Plant cells need sugar for energy to perform work, and for building other molecules. Animal cells do not contain starch, animals such as turkeys store excess sugar in the form of a plysaccharide called glycogen. Glycogen is a chain of many glucose monomers but a glycogen polymer is more highly branched than a starch polymer. Some polysaccharides in plants, such as cellulose, serve as building materials. They protect cells and stiffen the plant, preventing it from flopping over. Cellulose is made up of glucose monomers. Multiple cellulose chains are linked together with hydrogen bonds. Cellulose from the plant foods, commonly referred to as "fiber," passes unchanged through your digestive system. It helps keep your digestive system healthy, but it doesn't serve as a nutrient. Almost all carbohydrates are hydrophilic. It's due to the many hydroxyl groups in their sugar units.

Concept Check 5.2
1. Explain the difference between a monosaccharide and a disaccharide. Give an example of each.
Monosaccharides are simple sugars contain just one sugar unit and disaccharide is sugar with two monosacchrides. Glucose is an example of monosaccharides and sucrose is an example of disaccharide.

2. Compare and contrast starch, glycogen, and cellulose.
Starch is a polysaccharide found in plant cells that consists entirely of glucose monomers. Glycogen is polysaccharide in animal cells that consists of many glucose monomers. Cellulose is polysaccharide consisting of glucose monomers that reinforces plant-cell walls.

3. How do animals store excess glucose molecules?
Animals store excess sugar in the form of a polysaccharide called glycogen.