Organic compounds are compounds that contain carbon and are the basis of all living cells. There are four main classes of organic compounds found in cells. They are carbohydrates, lipids, proteins, and nucleic acids.
Carbohydrate is a fancy way of saying sugar. Carbohydrates can be very small or very large molecules, but they are still sugars. Most carbohydrates end with –ose; example: glucose.
A carbohydrate is called an ORGANIC compound because it contains CARBON. Sugars provide living things with energy. They sometimes act as substances used for structure; like the shell of a crab, or the stem of a plant. Scientists use the word “saccharide” to describe sugars. If there is only one sugar molecule, it is called a monosaccharide. If there are two it is a disaccharide. If there are a whole bunch, it is a polysaccharide.
A sugar called glucose is the most important monosaccharide on Earth. Glucose is used in cellular respiration and is created during photosynthesis. When you think of sugar, like the kind in candy, it is actually a disaccharide. Table sugar is made up of glucose and another monosaccharide called fructose.
Monosaccharides and disaccharides are usually referred to as simple sugars.
When several carbohydrates combine it is called a polysaccharide (poly means many). There can be hundreds of sugars combined in a chain. These chains are also known as “complex carbohydrates” or
“starches”. You can find polysaccharides in foods like pasta and potatoes.
Another important polysaccharide is cellulose. Cellulose is found in plants. It is one of those carbohydrates used for structure. Cellulose is in wood and the cell walls of plants. You know that shirt you’re wearing? If its cotton, that’s cellulose too!
You can test substances for the presence of carbohydrates. One test is for simple sugars, like glucose.
In this test you use a testing reagent called “Benedict’s solution”. It has a Windex=-like blue color. If simple sugars are present, the blue will change to an orange-red color when heated in a warm water bath for 3 minutes. Another test is for complex carbohydrates, or starches. The test reagent is “lugol’s iodine”. The solution is a reddish-brown color. If starch is present in the sample, the solution will change to a dark bluish-black.
Lipids are another type of ORGANIC molecule. When you think of fat, you should know that it is a lipid.
Lipids are also used to make STEROIDS and WAXES. So, if you pick out some earwax and smell it, that’s a lipids too. (OOOH gross!!!)
Fat is also known as a triglyceride. It is made up of a molecule known as GLYCEROL, which is connected to possibly one, two, or three fatty acids. Glycerol is the basis of all fats, made up of a three-carbon chain. It connects the fatty acids together. A FATTY ACID is a long chain of carbon atoms connected to each other.
There are two kinds of fats, Saturated and Unsaturated. Unsaturated fats have at least one double bond in one of the fatty acids. A double bond is when two electrons are shared or exchanged in a bond. They are much stronger than single bonds. Saturated fats have no double bonds.
Waxes are used to coat and protect things in nature. Bees make wax. Your ears make wax. Plant leaves have wax on the outside.

Fats have a lot of energy stored up in their bonds. That’s why the human body stores fat as an energy course. When it needs extra fuel, your body breaks down the fat and gets the energy. Where one molecule of sugar only gives a small amount of energy, a fat molecule gives off much more. You can detect a lipid by placing a sample in water. Lipids do not dissolve in water. Another test is the brown paper test; if brown paper turns opaque (translucent) upon contact with the substance, the substance contains lipids.
Proteins are made up of amino acids. Even though a protein can be very complex, it is basically a long chain of amino acids: all twisted around itself like a knot. Even though scientists have discovered over
50 amino acids, only 20 are used to make something called proteins in our bodies. Each amino acid is slightly different. Thousands of combinations of those twenty are used to make all of the proteins in your body. Amino acids bond together to make long chains. It is these chains that form proteins.
Proteins make up everything about you; your hair color, your eye color, your blood type, etc. Proteins are responsible for communication and recognition of cells in your body. Enzymes that help regulate chemical reactions, like digestive processes, are proteins. Proteins are very important.
A test for the presence of proteins is accomplished with a reagent known as “biuret reagent”. It is a bright, cobalt blue. If proteins are present, the color will change to a light lavender (purple).
Nucleic acids are the building blocks of living organisms. You may have heard of DNA described the same way. Guess what? DNA is just one type of nucleic acid. Some other types are rRNA, mRNA and tRNA. All of these “NAs” work together to help cells replicate and build proteins. NA? hold on… Might that stand for nucleic acid? It just might.
All nucleic acids are made up of the same building blocks….NUCLEOTIDES. These nucleotides are made of three pieces…
(1) A five carbon sugar.
(2) A base that has a nitrogen atom.
(3) An ion of phosphoric acid (H
3
PO
4
)
Nucleic acids are found in all cells. We do not test for their presence.