Principles of Biochemistry Volume 1 - A. Lehninger 1985

Biomolecules
Cells

Readers may wonder why, when embarking on a Structure/133.html">Discussion of biochemistry, we start with Cells. Of course, some of you may have already studied Cell biology. Nevertheless, it is essential to begin with The Cell because the vast majority of biochemical reactions under natural conditions occur within cells rather than in flasks or test tubes. The fundamental difference between biochemistry and "conventional" chemistry is that biochemical reactions take place under strictly limited conditions dictated by the dimensions of cells and their internal structure, as well as by the Physical and Chemical parameters compatible with cellular life.

Standard Chemical Reactions familiar to us are carried out in reaction vessels made of non-biological Materials, and the sizes of these vessels are disproportionately larger than the reacting molecules. Furthermore, conventional chemical reactions sometimes require high temperatures or pressures, aggressive Reagents, or electrical energy, and are frequently conducted in organic Solvents. In contrast to chemistry, biochemical reactions in living cells proceed within volumes tightly constrained by the dimensions of cells or their Organelles, whose remarkably fragile walls are often only a few molecules thick. Moreover, biochemical reactions take place exclusively in an aqueous environment at relatively low, constant temperatures. Cells cannot tolerate extreme temperatures or pressures, extreme acidity, or the presence of highly reactive compounds. As we subsequently examine the chemistry of biological processes, we must always keep in mind the size, structure, and properties of cells, constantly harmonizing The concepts of chemistry and cell biology.

In this chapter, we will focus on the Structure and Biochemical Properties of the most common cell types. In subsequent chapters, certain aspects of this topic will be explored in greater detail.

A structure lost within the Cell Cytoplasm.

A network or lattice of extremely fine filaments that constitutes the "ground substance" of animal cells under ultra-high magnification. Conventional electron Microscopy Techniques failed to reveal this network; it was discovered only recently thanks to a novel high-voltage, high-resolution Electron microscopy method. The figure illustrates only a minor portion of the cell cytoplasm, which is literally permeated by this intricate three-dimensional network.