LEHNINGER PRINCIPLES OF BIOCHEMISTRY - VOL. 1. THE FOUNDATIONS OF BIOCHEMISTRY: STRUCTURE AND CATALYSIS - 2011

PART I. STRUCTURE AND CATALYSIS

Biochemistry is, without exaggeration, the chemistry of life, and living organisms—in the truest sense—can be investigated, analyzed, and ultimately understood through their functional mechanisms. As students embark on The Study of biochemistry, mastering its language and foundational principles is essential; this is precisely what we will explore in Part I.

The chapters in Part I are dedicated to the Structure and function of the primary cellular building blocks: Water (Ch. 2), Amino Acids and Proteins (Ch. 3–6), Sugars and Polysaccharides (Ch. 7), NUCLEOTIDES and Nucleic Acids (Ch. 8), Fatty acids and Lipids (Ch. 10), and finally, membranes and membrane signaling proteins (Ch. 11 and 12). Each Class of molecules is introduced alongside a Discussion of the methodologies used to study them. While some techniques are woven directly into the core text, an entire chapter (Ch. 9) is devoted to biotechnology, encompassing cloning, Genomics, and Proteomics.

Our exploration of biochemistry begins with water (Ch. 2), as its properties are critical to the structure and function of all other cellular components. When examining each class of organic molecules, we will first look at the covalent interactions linking monomeric units (amino acids, Monosaccharides, nucleotides, and fatty acids), followed by The structure of macromolecules and the supramolecular complexes they form. The underlying theme of this approach is that polymeric macromolecules in living systems, despite their massive size, are highly ordered chemical compounds with strictly defined sequences of monomer units that dictate their structure and

function. This core concept rests on three interrelated principles: 1) the unique structure of each macromolecule dictates its function; 2) noncovalent interactions are vital to macromolecular structure and, consequently, to function; and 3) monomer units within polymeric macromolecules are linked in specific sequences that encode the information governing the Organization of living systems.

Structure-function relationships are particularly striking in proteins, which exhibit an extraordinary diversity of Functions. One specific Amino Acid Sequence forms the tough, fibrous strands of Hair and wool, another constitutes the protein that transports oxygen in the Blood, and a third binds other proteins and catalyzes the Cleavage of their internal bonds. Similarly, the Specialized Functions of polysaccharides, nucleic acids, and lipids are a direct manifestation of their chemical structure—that is, The properties of their monomer units and the precise order of their linkage into polymer chains. Linked sugars serve as Energy Sources, structural fibers, and specific recognition sites; nucleotides joined in DNA or RНК contain the master blueprint for the entire Organism; and lipid complexes form Introduction/36.html">Biological Membranes. Chapter 12 synthesizes these concepts of biomolecular function, describing how specific signaling systems regulate biomolecular activity and maintain Homeostasis at the cellular, organ, and whole-organism levels.

As we transition from monomer units to increasingly large polymer molecules, noncovalent forces—rather than covalent bonds—begin to play the primary role. Certainly, covalent bonds both within and between monomer units constrain the possible shapes a macromolecule can adopt. However, it is the myriad noncovalent interactions that determine a biomolecule's stable native conformation while rendering it sufficiently flexible for biological function. As we will see, noncovalent bonds are critical for enzymatic catalytic activity, complementary base pairing in nucleic acids, and the spatial arrangement and properties of Membrane Lipids.

The principle that monomer sequences encode specific information is most clearly illustrated in our discussion of nucleic acids (Ch. 8). However, proteins and certain low-molecular-weight sugars (Oligosaccharides) also function as informational molecules. The amino acid sequence of a protein contains the information that dictates its folding into a specific three-dimensional structure, ultimately determining its function. Likewise, certain oligosaccharides possess unique primary sequences and three-dimensional architectures recognized by other macromolecules.

Across all classes of Biomolecules, a consistent structural hierarchy is readily apparent: macromolecules are assembled from distinct monomer units via relatively stable bonds. The three-dimensional structures of these biomolecules are maintained through noncovalent interactions. Furthermore, these macromolecules can associate into supramolecular complexes and Organelles that carry out cellular metabolic functions. All the molecules described in Part I serve as the fundamental Building Blocks of life.