Learning Outcomes
Discuss why it is said that life is carbon-based and the bonding properties of carbon.
Carbon
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. Other elements play important roles in biological molecules, but carbon certainly qualifies as the “foundation” element for molecules in living things. It is the bonding properties of carbon atoms that are responsible for its important role.
Carbon Bonding
Carbon contains four electrons in its outer shell. Therefore, it can form four covalent bonds with other atoms or molecules. The simplest organic carbon molecule is methane (CH4), in which four hydrogen atoms bind to a carbon atom (Figure 1).
However, structures that are more complex are made using carbon. Any of the hydrogen atoms can be replaced with another carbon atom covalently bonded to the first carbon atom. In this way, long and branching chains of carbon compounds can be made (Figure 2a). The carbon atoms may bond with atoms of other elements, such as nitrogen, oxygen, and phosphorus (Figure 2b). The molecules may also form rings, which themselves can link with other rings (Figure 2c). This diversity of molecular forms accounts for the diversity of functions of the biological macromolecules and is based to a large degree on the ability of carbon to form multiple bonds with itself and other atoms.
Candela Citations
- Concepts of Biology. Authored by: Open Stax. Located at: http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.25. License: CC BY: Attribution. License Terms: Download for free at http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.25