Page 19 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioChemistry

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Bioenergetics 115

reactions is directly linked to the transmembrane flow of opportunity to unravel the mysteries of organisms from
protons into the lumen of the membrane. This proton flow planets other than Earth.
results in the generation of an electrochemical proton gra-
dient. Essentially, part of the light energy is conserved
by formation of this gradient as well as by formation of SEE ALSO THE FOLLOWING ARTICLES
the strong reducing agent NADPH. The flow of protons
provides the energy needed for the synthesis of the ter- CARBOHYDRATES • CARBON CYCLE • CHROMATIN
minal phosphate anyhydride bond of ATP, an example of STRUCTURE AND MODIFICATION • ELECTRON TRANS-
the conversion of the osmotic and electrical energy of the FER REACTIONS • ENERGY FLOWS IN ECOLOGY AND
proton gradient to chemical bond energy. The syntheses IN THE ECONOMY • ENERGY TRANSFER,INTRAMOLECU-
of ATP and NADPH capture some of the light energy. In LAR • ION TRANSPORT ACROSS BIOLOGICAL MEMBRANES
turn, ATP and NADPH drive the unfavorable reduction of • LIPOPROTEIN/CHOLESTEROL METABOLISM • PROTEIN
CO 2 by H 2 O to form carbohydrates and O 2 . SYNTHESIS • THERMODYNAMICS
Organisms, especially bacteria, have evolved novel
bioenergetic mechanisms that are well suited to their en-
vironments. For example, the bacterium Halobacter halo- BIBLIOGRAPHY
bium lives in salt marshes and requires NaCl at concentra-
tions that kill other organisms. These halophilic bacteria Cramer, W. A., and Knaff, D. B. (1990). “Energy Transduction in Bio-
contain patches of a purple protein, halorhodopsin, on its logical Membranes: A Text of Bioenergetics,” Springer-Verlag, New
York.
plasma membrane. Halorhodopsin is a light-driven proton
Garrett, R. H., and Grisham, C. M. (1999). “Biochemistry,” 2nd ed.,
pump and its operation causes protons to be ejected from Saunders College Publishing, Fort Worth.
the cells. The resulting electrochemical proton gradient McCarty, R. E. (1999). “Chemiosmotic Coupling,” In “Encyclopedia of
may be used to drive ATP synthesis or the transport of Molecular Biology” (T. Creighton, ed.), pp. 402–408, John Wiley and
biochemicals. Given the diversity of the environments in Sons, Inc., New York.
Nichols, D. G., and Ferguson, S. J. (1992). “Bioenergetics 2,” Academic
which organisms grow, it is possible that biochemists will
Press, London.
uncover new ways in which organisms meet their ener- Ort, D. R., and Yocum, C. F., eds. (1996). “Oxgenic Photosynthesis: The
getic needs. Perhaps future bioenergeticists will have the Light Reactions,” Kluwer Academic, Dordrechtshill, Norwell, MA.