The carbon atoms may bond with atoms of other elements, such as nitrogen, oxygen, and phosphorus ( Figure 2.13 b). In this way, long and branching chains of carbon compounds can be made ( Figure 2.13 a). Any of the hydrogen atoms can be replaced with another carbon atom covalently bonded to the first carbon atom. However, structures that are more complex are made using carbon. The simplest carbon molecule is methane (CH4), depicted here. Figure 2.12 Carbon can form four covalent bonds to create an organic molecule. The simplest organic carbon molecule is methane (CH 4), in which four hydrogen atoms bind to a carbon atom. Therefore, it can form four covalent bonds with other atoms or molecules. Carbon BondingĬarbon contains four electrons in its outer shell. It is the bonding properties of carbon atoms that are responsible for its important role.
Other elements play important roles in biological molecules, but carbon certainly qualifies as the “foundation” element for molecules in living things. It is often said that life is “carbon-based.” This means that carbon atoms, bonded to other carbon atoms or other elements, form the fundamental components of many, if not most, of the molecules found uniquely in living things. In addition, they may contain hydrogen, oxygen, nitrogen, phosphorus, sulfur, and additional minor elements. Biological macromolecules are organic, meaning that they contain carbon. Combined, these molecules make up the majority of a cell’s mass.
There are four major classes of biological macromolecules (carbohydrates, lipids, proteins, and nucleic acids), and each is an important component of the cell and performs a wide array of functions. The large molecules necessary for life that are built from smaller organic molecules are called biological macromolecules.