Molecular Biology of the Cell - Volume 2 - Alberts B., Bray D., Lewis J., Raff M., Roberts K., Watson J. 1993

Cell Growth and Division

Cells reproduce by doubling their internal contents followed by division into two. Complex sequences of Cell divisions, periodically interrupted by the fusion of Gametes, lead to The formation of Multicellular Organisms. In higher animals and plants, even after maturity is reached, Cell Division is typically required to replace losses resulting from cellular "wear and tear." In the adult human body, simply to maintain Homeostasis, millions of new Cells must be generated every second; if all cell divisions were to cease (as, for example, following massive radiation exposure), a person would die within a few days.

The doubling of many cellular components does not require strict control. If a cell contains numerous molecules or Organelles of a certain type, it is generally sufficient for their number to roughly double during a single cycle and then be distributed approximately evenly between the two daughter cells. However, there is at least one obvious exception: in the case of DNA, such duplication and distribution must be flawlessly precise, which requires a specialized mechanism. Therefore, when examining the Cell Cycle, it is sometimes convenient to distinguish between the chromosomal cycle and the parallel cytoplasmic cycle. In the chromosomal cycle, nuclear METABOLISM/36.html">DNA Replication (DNA Synthesis) alternates with mitosis, during which the replicated copies of The Genome are segregated. In the cytoplasmic cycle, cell growth—during which other cellular components double in number—alternates with cytokinesis, the division of the entire cell into two.

We will begin the chapter by discussing the coordination and regulation of these two interconnected cycles. We will examine the mechanisms that ensure that between any two cell divisions, all nuclear DNA is reliably duplicated exactly once, and we will see how the events of the chromosomal cycle are coordinated with those of the cytoplasmic cycle. Next, we will explore the Regulation of Cell division in Multicellular animals by extracellular environmental factors, a topic significantly clarified by recent breakthroughs in Cancer research. Finally, we will discuss the molecular mechanisms responsible for mitosis and cytokinesis. For these two processes to take place, the centrosome (see Section 13.5.2) must be faithfully inherited and accurately duplicated to form the two poles of the mitotic spindle; this centrosome cycle can be regarded as a third component of The Cell cycle.