The Composition and Architecture of the Cell

In chapter 1, we have seen how phospholipids can cooperatively assemble to form membrane structures, which resemble the membranes of biological cells. Now, let us take a look at the composition and organization of the cell, which will allow us to put the physics in its biological context. Some of the terms and concepts introduced in this chapter (e.g., proteins, cell membrane, etc.) will be dealt with in more details later on in this book, while others (such as those concerning the structure and function of cellular organelles, biochemistry of the cell, etc.) are explained in many excellent books that are available on molecular and cellular biology (e.g., Alberts et al., 2002; Lodish et al., 2004; Berg et al., 2002). The reader should therefore be aware that by no means do we intend in this section to provide a comprehensive review of subjects normally covered by cell biology and biochemistry textbooks. Instead, herein the biological information is reduced to its bare essentials, and it will be introduced and used only insofar as it can help the progression towards understanding of the biophysics concepts and principles presented in this book.

Broadly speaking, there are two classes of living systems: viruses and uni- or multi-cellular organisms. Of these, only cellular organisms present the two main distinguishing features of a living system, self-reproduction and metabolism, viruses not being endowed with their own metabolism. Both deoxyribonucleic-based (DNA) viruses and ribonucleic-based (RNA) viruses rely on the cellular metabolism of the host cell, in order to self-multiply.

Section 2.1 is concerned with a brief description of the organization of biological cells, which is considered to be the fundamental morphological and functional unit of living matter. Section 2.2 will provide a description of protein structure, folding and misfolding, while section 2.3 will discuss the DNA structure and replication (multiplication).