Macromolecules: Structure, Shape, and Information

Molecular Recognition Processes¹

Outline Introduction The Specific Interactions of a Macromolecule Depend on Weak, Noncovalent Bonds A Helix Is a Common Structural Motif in Biological Structures Made from Repeated Subunits Diffusion Is the First Step to Molecular Recognition Thermal Motions Bring Molecules Together and Then Pull Them Apart The Equilibrium Constant Is a Measure of the Strength of an Interaction Between Two Molecules Atoms and Molecules Move Very Rapidly Molecular Recognition Processes Can Never Be Perfect Summary Figures Figure 3-1: The size of protein molecules compared to some other cell components Tables Table 3-1: Approximate Chemical Compositions of a Typical Bacterium and a Typical Mammalian Cell Section References Cantor, C.R.; Schimmel, P.R.Biophysical Chemistry, Part I and Part III. New York: W.H. Freeman, 1980. Eisenberg, D.; Crothers, D.Physical Chemistry with Applications to the Life Sciences. Menlo Park, CA: Benjamin-Cummings, 1979. Pauling, L.The Nature of the Chemical Bond, 3rd ed. Ithaca, NY: Cornell University Press, 1960. Whitesides, G.M.; Mathias, J.P.; Seto, C.T.Molecular self-assembly and nanochemistry: a chemical strategy for the synthesis of nanostructures. Science 254:1312-1319, 1991 [PubMed]

Introduction     Macromolecules typically have molecular weights between about 10,000 and 1 million and are intermediate in size between the organic molecules of the cell discussed in Chapter 2 and the large macromolecular assemblies and organelles that will be discussed in subsequent chapters (Figure 3-1). One small molecule, water, constitutes 70% of the total mass of a cell; nearly all of the remaining cell mass is due to macromolecules (Table 3-1).     As described in Chapter 2, a macromolecule is assembled from low-molecular-weight subunits that are repeatedly added to one end to form a long, chainlike polymer. Usually only one family of subunits is used to construct each chain: amino acids are linked to other amino acids to form proteins, nucleotides are linked to other nucleotides to form nucleic acids, and sugars are linked to other sugars to form polysaccharides. Because the precise sequence of subunits is crucial to the function of a macromolecule, its biosynthesis requires mechanisms to ensure that the correct subunit goes into the polymer at each position in the chain.

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