Carbon and the Molecular Diversity of Life
Overview: Carbon – The Backbone of Biological Molecules
Although cells are 70–95% water, the rest consists mostly of carbon-based compounds.
Carbon is unparalleled in its ability to form large, complex, and diverse molecules.
Carbon accounts for the diversity of biological molecules and has made possible the great
diversity of living things.
Proteins, DNA, carbohydrates, and other molecules that distinguish living matter from
inorganic material are all composed of carbon atoms bonded to each other and to atoms of
These other elements commonly include hydrogen (H), oxygen (O), nitrogen (N), sulfur
(S), and phosphorus (P).
Concept 4.1 Organic chemistry is the study of carbon compounds
The study of carbon compounds,
deals with any compound with
carbon (organic compounds).
Organic compounds can range from simple molecules, such as CO
, to complex
molecules such as proteins, which may weigh more than 100,000 daltons.
The overall percentages of the major elements of life (C, H, O, N, S, and P) are quite
uniform from one organism to another.
However, because of carbon’s versatility, these few elements can be combined to build
an inexhaustible variety of organic molecules.
Variations in organic molecules can distinguish even between individuals of a single
Concept 4.2 Carbon atoms can form diverse molecules by bonding to four other
With a total of 6 electrons, a carbon atom has 2 in the first electron shell and 4 in the
Carbon has little tendency to form ionic bonds by losing or gaining 4 electrons to
complete its valence shell.
Instead, carbon usually completes its valence shell by sharing electrons with other atoms
in four covalent bonds.
by carbon makes large, complex molecules possible.
When carbon forms covalent bonds with four other atoms, they are arranged at the
corners of an imaginary tetrahedron with bond angles of 109.5°.