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Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002.

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Molecular Biology of the Cell. 4th edition.

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Chapter 17The Cell Cycle and Programmed Cell Death

“Where a cell arises, there must be a previous cell, just as animals can only arise from animals and plants from plants.” This cell doctrine, proposed by the German pathologist Rudolf Virchow in 1858, carried with it a profound message for the continuity of life. Cells are generated from cells, and the only way to make more cells is by division of those that already exist. All living organisms, from the unicellular bacterium to the multicellular mammal, are products of repeated rounds of cell growth and division extending back in time to the beginnings of life on Earth over three billion years ago.

A cell reproduces by performing an orderly sequence of events in which it duplicates its contents and then divides in two. This cycle of duplication and division, known as the cell cycle, is the essential mechanism by which all living things reproduce. In unicellular species, such as bacteria and yeasts, each cell division produces a complete new organism. In multicellular species, long and complex sequences of cell divisions are required to produce a functioning organism. Even in the adult body, cell division is usually needed to replace cells that die. In fact, each of us must manufacture many millions of cells every second simply to survive: if all cell division were stopped—by exposure to a very large dose of x-rays, for example—we would die within a few days.

The details of the cell cycle vary from organism to organism and at different times in an organism's life. Certain characteristics, however, are universal. The minimum set of processes that a cell has to perform are those that allow it to accomplish its most fundamental task: the passing on of its genetic information to the next generation of cells. To produce two genetically identical daughter cells, the DNA in each chromosome must first be faithfully replicated to produce two complete copies, and the replicated chromosomes must then be accurately distributed (segregated) to the two daughter cells, so that each receives a copy of the entire genome (Figure 17-1).

Figure 17-1. The cell cycle.

Figure 17-1

The cell cycle. The division of a hypothetical eucaryotic cell with two chromosomes is shown to illustrate how two genetically identical daughter cells are produced in each cycle. Each of the daughter cells will often divide again by going through additional (more...)

Eucaryotic cells have evolved a complex network of regulatory proteins, known as the cell-cycle control system, that governs progression through the cell cycle. The core of this system is an ordered series of biochemical switches that control the main events of the cycle, including DNA replication and the segregation of the replicated chromosomes. In most cells, additional layers of regulation enhance the fidelity of cell division and allow the control system to respond to various signals from both inside and outside the cell. Inside the cell, the control system monitors progression through the cell cycle and delays later events until earlier events have been completed. Preparations for the segregation of replicated chromosomes, for example, are not permitted until DNA replication is complete. The control system also monitors conditions outside the cell. In a multicellular animal, the system is highly responsive to signals from other cells, stimulating cell division when more cells are needed and blocking it when they are not. The cell-cycle control system therefore has a central role in regulating cell numbers in the tissues of the body. When the system malfunctions, excessive cell divisions can result in cancer.

In addition to duplicating their genome, most cells also duplicate their other organelles and macromolecules; otherwise, they would get smaller with each division. To maintain their size, dividing cells must coordinate their growth (i.e., their increase in cell mass) with their division; it is still not clear how this coordination is achieved.

This chapter is concerned primarily with how the various events of the cell cycle are controlled and coordinated. We begin with a brief overview of these events, the molecular details of which are discussed in other chapters (DNA replication in Chapter 5; chromosome segregation and cell division in Chapter 18). We then describe the cell-cycle control system, examining how it organizes the sequence of cell-cycle events and how it responds to intracellular signals to regulate cell division. We next discuss how multicellular organisms eliminate unwanted cells by the process of programmed cell death, or apoptosis, in which a cell commits suicide when the interests of the organism demand it. Finally, we consider how animals regulate cell numbers and cell size—using extracellular signals to control cell survival, cell growth, and cell division.


An Overview of the Cell Cycle

Components of the Cell-Cycle Control System

Intracellular Control of Cell-Cycle Events

Programmed Cell Death (Apoptosis)

Extracellular Control of Cell Division, Cell Growth, and Apoptosis


By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

Copyright © 2002, Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter; Copyright © 1983, 1989, 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson .
Bookshelf ID: NBK21056


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