Carbohydrates are composed of carbon, hydrogen, and oxygen and have the general formula (C1H2O1)n. They provide energy and structure to cells and are precursors of numerous important biological molecules. Monosaccharide monomers can be connected by glycosidic linkages to form disaccharides, oligosaccharides, and polysaccharides.
learning outcomes
You should be able to:
Identify the primary functions of carbohydrates in living organisms.
Explain why polysaccharides are useful structures for energy storage.
Use the chemical structures of polysaccharides to explain their properties.
What qualities of the polysaccharides starch and glycogen make them useful for energy storage?
Starch and glycogen have many carbon atoms bonded covalently to one another. These covalent bonds require energy for formation and release energy when broken.
After looking at the cellulose molecule in Figure 3.18A, can you see why a large number of hydrogen bonds are present in the linear structure of cellulose shown in Figure 3.18B? Why is this structure so strong?
The many hydrogen bonds between polysaccharide chains of cellulose hold them together, and the covalent bonds within the chains are strong individually.
You have seen how amino acid monomers form protein polymers and how sugar monomers form the polymers of carbohydrates. Now we will look at the lipids, which are unique among the four classes of large biological molecules in that they are not, strictly speaking, polymers.