 In this video I will describe the building blocks, structure, and functions of carbohydrates including monosaccharides, disaccharides, and polysaccharides. A carbohydrate is a chemical that has the basic formula of CH2O that can be repeating in order to form larger molecules. What we see in the illustration here is a polymer of monosaccharide monomers. This particular polymer is known as amylose, but any polymer formed from monomers that are carbohydrates is known as a polysaccharide. Amylose is one example of a polysaccharide. In amylose the monomers are glucose. Amylose is a form of starch that is a polysaccharide that is produced by plant cells. When you eat rice or wheat, when you're eating the products that are made from those grains, things like pasta or bread, one of the major nutrients that's found in that is the starch amylose. Amylose has a repeating unit, the monomer glucose. Multiple glucose monomers were linked together by dehydration synthesis in order to form amylose. And when we digest starches like amylose, we perform hydrolysis reactions to break down amylose, releasing smaller carbohydrates such as maltose and eventually glucose. Monosaccharides are the monomers of carbohydrates. Multiple monosaccharides will be linked together in order to form polysaccharides. Glucose is a major monosaccharide that we will see repeatedly as we go through the semester because glucose is an important energy source used by cells in our body. Fructose is the sugar that gives a sweet flavor to fruit and honey. And then galactose is one of the monosaccharides that's forming the milk sugar lactose. Deoxyribose and ribose are five-carbon monosaccharides in contrast to glucose, fructose, and galactose, which are six-carbon monosaccharides. So collectively the six-carbon monosaccharides are called hexoses, and the five-carbon monosaccharides are known as pentoses. Deoxyribose and ribose are important because they form a portion of the nucleotide structure, the nucleotides that are used to make DNA contain deoxyribose, and the nucleotides that are used to make RNA contain ribose. A disaccharide is a dimer of two monosaccharides that have been joined together by dehydration synthesis. The top left here we see sucrose, which is a disaccharide formed from one glucose and one fructose monomer that have been joined together in dehydration synthesis. In the top right here we see lactose, which is milk sugar, a disaccharide formed from one glucose monomer and one galactose monomer. In the bottom right we see maltose, a disaccharide that's formed from two glucose monomers. Polysaccharides are the polymers of carbohydrates formed by dehydration synthesis of several monosaccharides. Here we see several examples of polysaccharides. These starches amylose and amylopectin are long chains of glucose that are formed by plant cells. Glycogen is a long chain of glucose monomers that's formed in animal cells. Cellulose is also a polymer of glucose monomers. However, the arrangement of covalent bonds in cellulose prevents us from being able to digest cellulose, and therefore cellulose is considered nutritionally as a dietary fiber because it is indigestible.