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Biopolymers 245

(sometimes after minor conformational changes) onto the Within ribosomes, strong interactions between protein
surface of another. and r-RNA are essential for maintenance of the structure
Proteins, in particular, must be able to interact with and functioning of the ribosome. Details of these interac-
other polymers, for enzymes are involved in the synthesis tions are not yet well understood.
and degradation of all biopolymers. In addition, however, Polysaccharide-polysaccharide interactions can also
many examples are known of associations between nonen- take place, probably involving extensive hydrogen bond-
zymic proteins and other proteins, polysaccharides, or nu- ing and “shape fitting” over lengths of twenty or more
cleic acids. Muscle movement, for example, is brought monosaccharide residues. This is important in plant cell
aboutandcontrolledbycomplexinteractionsbetweensev- walls where cellulose fibers are embedded in a matrix of
eral proteins (myosin, actin, troponin, and tropomyosin) proteins and several different polysaccharides.
while collagen fibers are associated with both glycopro-
teins and proteoglycans in connective tissues. Protein an-
tibodies can bind to protein or polysaccharide antigens, SEE ALSO THE FOLLOWING ARTICLES
while polypeptide hormones must be recognized by their
receptors, themselves proteins or glycoproteins. The pro- BIOMATERIALS,SYNTHESIS,FABRICATION, AND APPLI-
teins that interact with nucleic acids (e.g., repressors) bind CATIONS • GLYCOPROTEINS AND CARBOHYDRATES • HY-
to specific base sequences or secondary structures on the DROGEN BONDS • POLYMER PROCESSING • POLYMERS,
polymeric acids. In some cases these base sequences are RECYCLING • POLYMERS,STRUCTURE • POLYMERS,
almost palindromic (read the same backward or forward) SYNTHESIS
as in XV, and the protein molecules which bind to them
often have two subunits so that one may bind to each strand
of the DNA.
BIBLIOGRAPHY
5 end ---- GT TCACTC TGAAC---- 3 end

Branden, C., and Tooze, J. (1999). “Introduction to Protein Structure,”

3 end ---- CAAGTGAGACT T G- ---5 end 2nd ed., Garland Publishing Inc., New York.
Dey, P. M., and Harborne, J. B. (1997). “Plant Biochemistry,” Academic
XV Press, New York.
Dumitriu, S., ed. (1998). “Polysaccharides,” Marcel Dekker, New York.
Fried, J. R. (1995). “Polymer Science and Technology,” Prentice-Hall,
A “motif” found in several DNA-binding proteins con- New Jersey.
Neidle, S., ed. (1998). “Oxford Handbook of Nucleic Acid Structure,”
sists of two helices linked by a short stretch of polypeptide
Oxford University Press, New York.
chain in the form of a sharp bend. Such an arrangement Voet, D., Voet, J. G., and Pratt, C. W. (1999). “Fundamentals of Bio-
fits easily into a groove of double helical DNA. chemistry,” John Wiley & Sons, New York.