Biologically Important Molecules
Carbohydrates, Proteins, Lipids, and Nucleic Acids
Objectives
In this lab you will learn to:
1. Perform tests to detect the presence of carbohydrates, lipids, proteins, and nucleic acids
2. Recognize the importance of a control in a biochemical test
3. Use biochemical tests to identify an unknown compound
Introduction
Organic molecules are those primarily made up of carbon, hydrogen and oxygen. The common organic compounds of living organisms are carbohydrates, proteins, lipids, and nucleic acids. Each of these macromolecules (polymers) are made of smaller subunits (monomers). The bonds between these subunits are formed by dehydration synthesis. This process requires energy; a molecule of water is removed
(dehydration) and a covalent bond is formed between the subunits (Fig 1). Breaking this bond is called hydrolysis; it requires the addition of a water molecule and releases energy. Figure 1. Dehydration synthesis and hydrolysis of a polymer.
Each class of these macromolecules has different structures and properties. For example, lipids (composed of fatty acids) have many C-H bonds and relatively little oxygen, while proteins (composed of amino acids) have amino groups (-NH3+) and carboxyl (-COOH) groups. These characteristic subunits and chemical groups impart different properties to the macromolecules.
For
example, monosaccharides such as glucose are polar and soluble in water, whereas lipids are nonpolar and insoluble in water.
Methods for Identifying Organic Compounds
There are several chemical tests available for the identification of the major types of organic compounds in living organisms. Typically these tests are used to determine the makeup of an unknown material. For instance, a forensic detective may be interested in a identifying a fluid found at a crime scene. The collected fluid is the unknown. As the tests are carried out, the detective will