Molecular Biology of the Cell - Volume 1 - Alberts B., Bray D., Lewis J., Raff M., Roberts K., Watson J. 1994

Introduction to Cell Biology
Evolution of the Cell

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Fig. 1.1. Bacterial Cells on the HEAD of a pin (scanning electron micrographs). (Courtesy of Tony Brain and Science Photo Library.)

Fig. 1.II. Dividing Yeast cells (scanning electron micrograph). (Courtesy of Herskowitz and Schabatach.)

All living things are made of cells—small, membrane-enclosed compartments filled with a concentrated aqueous solution of chemicals. The simplest forms of life are solitary cells that propagate by division. More highly developed organisms, such as ourselves, can be compared to cellular cities, in which specialized Functions are carried out by groups of cells, which in turn are linked by complex systems of communication. In a sense, cells are halfway between molecules and humans. We study cells to understand their molecular Structure, on the one hand, and to discover how they interact to form an Organism as complex as a human being, on the other.

It is believed that all organisms and all their constituent cells have evolved from a common ancestral cell. The two main processes of evolution are 1) random Changes in the Genetic information passed from an organism to its offspring, and 2) the Selection of genetic information that promotes the survival and reproduction of its carriers. Evolutionary theory is the central principle of biology, allowing us to make sense of the staggering Water/126.html">Diversity of the living world.

This chapter, like the book as a whole, is devoted to development—from molecules to Multicellular Organisms. It discusses the Evolution of the Cell, first as a self-reproducing unit composed of smaller parts, and then as a building block for larger structures. As the material unfolds, we will progressively introduce the components and Functions of the cell, which are examined in detail in subsequent chapters, largely in the same order. We will learn how The properties of large molecules of a specific type ensure the transmission to offspring and the phenotypic expression (expression) of hereditary information, driving the evolutionary process. These molecules, enclosed in a membrane, constitute The Essence of a self-replicating cell. We will then describe the major stages of evolution—from small, Bacteria-like cells to much larger and more complex ones, such as the cells of modern plants and animals. Finally, hypotheses will be proposed as to how individual free-living cells gave rise to large multicellular organisms, how cells specialized, and how, by combining, they formed Organs as complex as the brain.

Naturally, there are dangers in an evolutionary approach: we fill large gaps in our knowledge with speculation, the details of which may be wrong. It is not in our power to go back in time and witness the unique molecular events that occurred billions of years ago. However, these ancient events have left many traces that we can analyze. Ancestral plants, animals, and even bacteria have been preserved as fossils. But even more importantly, every modern organism contains information about the traits of living organisms in the past. In particular, existing biological molecules allow us to trace the evolutionary path, demonstrating fundamental similarities between the most distantly related living organisms and revealing certain differences between them. By analyzing molecular Similarities and differences, we attempt to reconstruct the traits of creatures that once lived. This task can be compared to that of a philologist reconstructing the text of an ancient author, distorted by repeated copying and editing. The task is difficult and the evidence is imperfect, yet this approach makes it possible to make reasonable assumptions about the Main stages in the evolution of living cells.