Unit D

Module 6 ~ Lesson 1


A macromolecule, by definition, implies "a large molecule." In biology, this refers to carbohydrates, lipids, proteins, and nucleic acids. Known as the building blocks of all the structures within people's bodies, these macromolecules are used to store energy, build structures, or store genetic material. Carbohydrates can be turned into fats and stored in bodies, while muscles and organs have large amounts of proteins in their structure. Lipids comprise membranes because of their insoluble nature in water. Nucleic acids are the building blocks of human genetic code found in your DNA.

Read the information in the tabs below to learn more about each macromolecule.

Monosaccharides are more commonly referred to as simple sugars. They are the monomer for disaccharides and polysaccharides (starch). The image to the left shows five important simple sugars. You are not expected to memorize these names or structures.

Monosaccharides and disaccharides taste sweet and are found in fruits and refined sugar products.

Three polysaccharides that are important in human nutrition are starch, glycogen, and cellulose. All three are composed of many glucose monomers but have slightly different structures as can be seen in the image to the right. Starch is the energy storage molecule for plants and an important source of energy in the human diet. Cellulose is the hard woody substance in plants that provides structure. You might be familiar with the term fibre. Cellulose is important in the human diet to keep bulk and moisture in foods passing through the digestive system. Glycogen is the energy storage molecule in the human body. It can be found in the liver and, in smaller amounts, in muscle tissue.
By OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

Proteins are complex molecules composed of single units of amino acids. Long chains of amino acids are called peptide chains. Proteins are made of multiple peptide chains that are folded and bent around each other in a specific shape. Proteins have many functions and make up many structures in the human body.

Roger Daniels. February 1, 2010. Retrieved from Wikipedia CC-BY-SA3.0

Lipids, more commonly referred to as fats, are composed of a glycerol backbone and three fatty acid molecules. Lipids are an important energy storage molecule in the body as well as important in the structure and function of cell membranes and hormones as they do not dissolve in water.


Read the introductory information, "Assembling Macromolecules", "Disassembling Macromolecules", "Carbohydrates", "Proteins", "Nucleic Acids", and "Vitamins and Minerals" on pages 206 to 214 of the textbook.

Anabolic and Catabolic Reactions

Organic molecules contain carbon and form the basis of most living things. It has been estimated that in nature there are millions more organic compounds than there are inorganic compounds. All four of the macromolecules that you have just read about—carbohydrates, lipids, proteins, and nucleic acids—are organic compounds. Each of these complex molecules is formed from simpler subunits in an anabolic reaction. The dehydration synthesis reaction described on page 207 of your textbook is a type of anabolic reaction.

Each macromolecule may be broken down again into its original repeating simpler subunits through catabolic reactions. In a catabolic reaction, molecules are broken down into smaller components, and energy is released. The breakdown of food in digestion is a catabolic reaction. The hydrolysis reaction described in your textbook on page 207 is an example of a type of catabolic reaction. Note that both of these reactions require enzymes to take place.


Watch the following video that shows the processes of dehydration synthesis and the hydrolysis of sucrose and a protein. As you are watching, notice that for each bond formed (dehydration synthesis), another water molecule is produced. For each bond broken (hydrolysis), another water molecule is required.