Small Molecules, Energy, and Biosynthesis

Biosynthesis and the Creation of Order¹⁷

Outline Introduction The Free-Energy Change for a Reaction Determines Whether It Can Occur Biosynthetic Reactions Are Often Directly Coupled to ATP Hydrolysis Coenzymes Are Involved in the Transfer of Specific Chemical Groups The Structure of Coenzymes Suggests That They May Have Originated in an RNA World Biosynthesis Requires Reducing Power Biological Polymers Are Synthesized by Repetition of Elementary Dehydration Reactions Summary Section References Prigogine, I.; Stengers, I.Order out of Chaos: Man's New Dialogue with Nature. New York: Bantam Books, 1984.

Summary     The hydrolysis of ATP is commonly coupled to energetically unfavorable reactions, such as the biosynthesis of macromolecules, by the transfer of phosphate groups to form reactive phosphorylated intermediates. Because the energetically unfavorable reaction now becomes energetically favorable, ATP hydrolysis is said to drive the reaction. Polymeric molecules such as proteins, nucleic acids, and polysaccharides are assembled from small activated precursor molecules by repetitive dehydration reactions that are driven in this way. Other reactive molecules, called coenzymes, transfer other chemical groups in the course of biosynthesis: NADPH transfers hydrogen as a proton plus two electrons (a hydride ion), for example, whereas acetyl CoA transfers acetyl groups.

© 1994 by Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson.