Nucleic acid
The nucleic acids are DNA and RNA, or deoxyribonucleic acid and ribonucleic acid, respectively. They make the proteins that are present in almost every structure and perform almost every function in your body. DNA has a twisted ladder-like form, while RNA has many different shapes, depending on its function. DNA typically remains within the center, or nucleus, of a cell; RNA can travel throughout the cell to where it is needed. The backbones of both substances consist of alternating molecules of phosphate and sugar. Nucleotide bases make up the "rungs" attached to the backbone. Of the two types of nucleic acids, DNA is more stable, making it less likely to be broken down than RNA. Your genes are made up of DNA, and each gene provides the code for making a specific protein. RNA helps DNA to make these proteins.
Proteins
Proteins are probably the most versatile of all the organic molecules, making up many structures and executing various functions within organisms. Building blocks called amino acids make up proteins. About 20 different amino acids combine to form all of the various types of proteins on Earth. These amino acids all have almost the exact same composition; the only difference is the R group, which differs in each of the amino acids and gives them their uniqueness. When a protein is made, the protein comes together one amino acid at a time within the ribosome -- a structure that houses protein synthesis. Proteins have four levels of structure: The primary structure is the bonding of amino acids to one another; the secondary structure refers to the folds in certain areas within the protein; the tertiary structure is the ultimate three-dimensional look of the protein; and the quaternary structure consists of smaller protein subunits chemically bonded together to form a larger protein.
Carbohydrates
Carbohydrates comprise the largest number of organic molecules in organisms. Basically, carbohydrates are sugars; their origin can be traced to photosynthesis, the process by which organisms such as plants use sunlight to transform carbon dioxide and water into food. The simplest sugar is glucose, a molecule used to provide fuel for many types of organisms, including humans. The sugars found in foods include: fructose in fruits, galactose in milk, maltose in vegetables and sucrose in table sugar. The starch found in whole grains and vegetables is a complex carbohydrate made of chains of simpler glucose molecules. Your body contains an enzyme called amylase, which breaks down carbohydrates in the food you eat into glucose, which your cells can use as energy.
Lipids
Lipids, perhaps better known as fats, come in different forms in your body and contain the most energy of all the organic compounds. When your body burns lipids for fuel, you get more energy than if you burned the other organic molecules. In your body, fats perform many functions, taking the form of phospholipids and cholesterol, both important components of cell membranes; waxes that provide plants and animals with a protective layer; hormones that signal different functions in your body; vitamins that aid in different cell functions; and steroids, which are important in a number of physiological processes. Fats from animals tend to be more viscous than fats from plants.