All living organisms are composed of similar chemical compounds, called biomolecules. Biomolecules are organic molecules, meaning that they contain carbon-to-carbon or carbon-to-hydrogen bonds. Methane is one of the simplest organic molecules.
Notice that the central carbon atom, by sharing electrons, has formed chemical bonds with four hydrogen atoms. Carbon is important for life because it's a very versatile atom. In addition to hydrogen, carbon can bind with a number of other atoms, including oxygen, nitrogen, phosphorus, and sulfur.
Carbon can also bond to itself, forming chains, branch chains, and ring structures. It is also possible for carbon to form double bonds with itself, or bond to other elements, such as the oxygen shown here. The carbon chain of a biomolecule is called its skeleton, or backbone. This terminology makes sense because, just as your skeleton accounts for your shape, so too does the carbon skeleton of a biomolecule account for its shape. The reactivity of a biomolecule is mostly dependent on the functional group that attaches to its carbon backbone.
A functional group is a specific group of bonded atoms that always has the same chemical properties and always reacts in the same way. The functional group shown here is a hydroxyl group, and when it attaches to this carbon skeleton, the compound ethanol is formed. There are many different types of functional groups. In biology, the...
The five that you will probably come in contact with the most are the hydroxyl group, the carboxyl group, the amino group, the sulfhydryl group, and the phosphate group. In these diagrams, the R refers to where the functional group attaches to the carbon skeleton. The presence of a functional group changes the chemical reactivity of the biomolecule. Functional groups, therefore, help determine the identity of the biomolecule.
For example, when the carboxyl group shown here attaches to this carbon backbone, a fatty acid biomolecule is formed. When an amino group and a carboxyl group join with this carbon backbone, an amino acid biomolecule is formed. All biomolecules can be divided into four classes.
Proteins, carbohydrates, nucleic acids, and lipids. We'll discuss these different classes in depth in the next few tutorials.