Part I Structure and catalysis suite of modern advances in biotechnology that have ism; and aggregated lipids form membranes. Chapter 12 greatly accelerated the pace of discovery unifies the discussion of biomolecule function describ- The molecules found in a cell are a major part o ing how specific signaling systems regulate the activities the language of biochemistry; familiarity with them is a of biomolecules-within a cell, within an organ, and prerequisite for understanding more advanced topics among organs--to keep an organism in homeostasis covered in this book and for appreciating the rapidl As we move from monomeric units to larger and growing and exciting literature of biochemistry. We be- larger polymers, the chemical focus shifts from covalent gin with water because its properties affect the struc- bonds to noncovalent interactions. The properties of co- ture and function of all other cellular constituents. For valent bonds both in the monomeric subunits and in the each class of organic molecules, we first consider the bonds that connect them in polymers, place constraints covalent chemistry of the monomeric units (amino on the shapes assumed by large molecules. It is the nu- acids, monosaccharides, nucleotides, and fatty acids merous noncovalent interactions. however. that dictate and then describe the structure of the macromolecules the stable native conformations of large molecules while and supramolecular complexes derived from them. An permitting the flexibility necessary for their biological overriding theme is that the polymeric macromolecules function. As we shall see, noncovalent interactions are in living systems, though large, are highly ordered chem- essential to the catalytic power of enzymes, the critical ical entities, with specific sequences of monomeric sub interaction of complementary base pairs in nucleic units giving rise to discrete structures and functions. acids, the arrangement and properties of lipids in mem- This fundamental theme can be broken down into three branes, and the interaction of a hormone or growth fac interrelated principles: (1) the unique structure of each tor with its membrane receptor macromolecule determines its function; (2)noncovalent The principle that sequences of monomeric sub- interactions play a critical role in the structure and thus units are rich in information emerges most fully in the the function of macromolecules; and 3) the monomeric discussion of nucleic acids(Chapter 8). However, pro- subunits in polymeric macromolecules occur in specific teins and some short polymers of sugars (oligosaccha- equences, representing a form of information upon rides) are also information-rich molecules. The amino which the ordered living state depends cid sequence is a form of information that directs the The relationship between structure and function is folding of the protein into its unique three-dimensional especially evident in proteins, which exhibit an extraor- structure, and ultimately determines the function of the dinary diversity of functions. One particular polymeric protein. Some oligosaccharides also have unique se- equence of amino acids produces a strong, fibrous struc- quences and three-dimensional structures that are rec- ture found in hair and wool; another produces a protein ognized by other macromolecules that transports oxygen in the blood; a third binds other Each class of molecules has a similar structural proteins and catalyzes the cleavage of the bonds between hierarchy: subunits of fixed structure are connected by their amino acids. Similarly, the special functions of poly- bonds of limited flexibility to form macromolecules with saccharides, nucleic acids, and lipids can be understood three-dimensional structures determined by noncova- as a direct manifestation of their chemical structure with lent interactions. These macromolecules then interact their characteristic monomeric subunits linked in pre- to form the supramolecular structures and organelles cise functional polymers. Sugars linked together become that allow a cell to carry out its many metabolic func- energy stores, structural fibers, and points of specific tions. Together, the molecules described in Part I are molecular recognition; nucleotides strung together in the stuff of life. We begin with water. DNA or RNa provide the blueprint for an entire organ-suite of modern advances in biotechnology that have greatly accelerated the pace of discovery. The molecules found in a cell are a major part of the language of biochemistry; familiarity with them is a prerequisite for understanding more advanced topics covered in this book and for appreciating the rapidly growing and exciting literature of biochemistry. We be￾gin with water because its properties affect the struc￾ture and function of all other cellular constituents. For each class of organic molecules, we first consider the covalent chemistry of the monomeric units (amino acids, monosaccharides, nucleotides, and fatty acids) and then describe the structure of the macromolecules and supramolecular complexes derived from them. An overriding theme is that the polymeric macromolecules in living systems, though large, are highly ordered chem￾ical entities, with specific sequences of monomeric sub￾units giving rise to discrete structures and functions. This fundamental theme can be broken down into three interrelated principles: (1) the unique structure of each macromolecule determines its function; (2) noncovalent interactions play a critical role in the structure and thus the function of macromolecules; and (3) the monomeric subunits in polymeric macromolecules occur in specific sequences, representing a form of information upon which the ordered living state depends. The relationship between structure and function is especially evident in proteins, which exhibit an extraor￾dinary diversity of functions. One particular polymeric sequence of amino acids produces a strong, fibrous struc￾ture found in hair and wool; another produces a protein that transports oxygen in the blood; a third binds other proteins and catalyzes the cleavage of the bonds between their amino acids. Similarly, the special functions of poly￾saccharides, nucleic acids, and lipids can be understood as a direct manifestation of their chemical structure, with their characteristic monomeric subunits linked in pre￾cise functional polymers. Sugars linked together become energy stores, structural fibers, and points of specific molecular recognition; nucleotides strung together in DNA or RNA provide the blueprint for an entire organ￾ism; and aggregated lipids form membranes. Chapter 12 unifies the discussion of biomolecule function, describ￾ing how specific signaling systems regulate the activities of biomolecules—within a cell, within an organ, and among organs—to keep an organism in homeostasis. As we move from monomeric units to larger and larger polymers, the chemical focus shifts from covalent bonds to noncovalent interactions. The properties of co￾valent bonds, both in the monomeric subunits and in the bonds that connect them in polymers, place constraints on the shapes assumed by large molecules. It is the nu￾merous noncovalent interactions, however, that dictate the stable native conformations of large molecules while permitting the flexibility necessary for their biological function. As we shall see, noncovalent interactions are essential to the catalytic power of enzymes, the critical interaction of complementary base pairs in nucleic acids, the arrangement and properties of lipids in mem￾branes, and the interaction of a hormone or growth fac￾tor with its membrane receptor. The principle that sequences of monomeric sub￾units are rich in information emerges most fully in the discussion of nucleic acids (Chapter 8). However, pro￾teins and some short polymers of sugars (oligosaccha￾rides) are also information-rich molecules. The amino acid sequence is a form of information that directs the folding of the protein into its unique three-dimensional structure, and ultimately determines the function of the protein. Some oligosaccharides also have unique se￾quences and three-dimensional structures that are rec￾ognized by other macromolecules. Each class of molecules has a similar structural hierarchy: subunits of fixed structure are connected by bonds of limited flexibility to form macromolecules with three-dimensional structures determined by noncova￾lent interactions. These macromolecules then interact to form the supramolecular structures and organelles that allow a cell to carry out its many metabolic func￾tions. Together, the molecules described in Part I are the stuff of life. We begin with water. 46 Part I Structure and Catalysis 8885d_c01_046 12/30/03 6:35 AM Page 46 mac76 mac76:385_reb: