Essential Cell Biology 5th edition

CHAPTER FOURTEEN
14
Energy Generation in
Mitochondria and Chloroplasts
The fundamental need to generate energy efficiently has had a profound
influence on the history of life on Earth. Much of the structure, function,
and evolution of cells and organisms can be traced to their quest for
energy. Oxygen did not appear in the atmosphere until more than a billion
years after the first cells appeared on Earth. It is therefore thought
that the earliest cells may have produced ATP by breaking down organic
molecules that had been generated by geochemical processes. Such fermentation
reactions, discussed in Chapter 13, can occur in the cytosol
of present-day cells, when they use the energy derived from the partial
oxidation of energy-rich food molecules to form ATP.
But very early in the history of life, a much more efficient mechanism
for generating energy and synthesizing ATP appeared—one based on the
transport of electrons along membranes. This mechanism is so central
to the survival of life on Earth that we devote this entire chapter to it.
Membrane-based electron transport first appeared in bacteria more than
3 billion years ago, and the progeny of these pioneering cells currently
crowd every crevice of our planet’s land and oceans in a wild menagerie
of living forms. Perhaps most remarkably, remnants of these energygenerating
electron-transport systems can be found in the bacterial
descendants that labor within living eukaryotic cells: chloroplasts and
mitochondria.
In this chapter, we consider the molecular mechanisms that enable electron-transport
systems to generate the energy that cells need to survive.
We begin with a brief overview of the general principles central to the
generation of energy in all living things: the use of a membrane to harness
the energy of moving electrons. We describe how such processes
MITOCHONDRIA AND
OXIDATIVE PHOSPHORYLATION
MOLECULAR MECHANISMS OF
ELECTRON TRANSPORT AND
PROTON PUMPING
CHLOROPLASTS AND
PHOTOSYNTHESIS
THE EVOLUTION OF ENERGY-
GENERATING SYSTEMS