Chapter 4 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
Carbon is unparalleled in its ability to form large, complex, and diverse
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 other elements.
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, organic chemistry, deals with any compound
with carbon (organic compounds).
Organic compounds can range from simple molecules, such as CO2 or CH4, to
complex molecules such as proteins, which may weigh more than 100,000
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
The science of organic chemistry began in attempts to purify and improve the
yield of products obtained from other organisms.
Initially, chemists learned to synthesize simple compounds in the laboratory, but
had no success with more complex compounds.
The Swedish chemist Jons Jacob Berzelius was the first to make a distinction
between organic compounds that seemed to arise only in living organisms and
inorganic compounds that were found in the nonliving world.
This led early organic chemists to propose vitalism, the belief that physical and
chemical laws did not apply to living things.
Support for vitalism began to wane as organic chemists learned to synthesize
complex organic compounds in the laboratory.