19.1: Introduction
- Page ID
- 89031
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Bacteria divide by binary fission, duplicating their nearly “naked” circular chromosomes as the cell enlarges and divides into two daughter cells. Under favorable conditions, bacteria (e.g., E. coli) can divide every twenty to forty minutes. Many eukaryotic cells stop dividing when they reach maturity (their terminally differentiated state), while those that do divide may have varying life spans between divisions, ranging from fifteen to twenty-four hours. Cell division begins with mitosis, the condensation of chromosomes from chromatin. Cytokinesis is the process near the end of mitosis that physically divides one cell into two new cells after the duplicated chromosomes are safely on opposite sides of the cell. Although mitosis lasts only about an hour in the life of the typical eukaryotic cell, it has been parsed into four or five phases (depending on whose text you are reading!); it is the last of these phases that overlaps cytokinesis. Usually, mitosis and cytokinesis together take about 1.5 hours. By far the longest period between successive cell divisions or the cell cycle is interphase, so-called because nineteenth-century microscopists who described mitosis saw nothing happening in cells when they were not actually dividing. But by the 1970s, experiments had shown that interphase itself was divisible into discrete phases of cellular activity called \(\rm G_1\), S, and \(\rm G_2\) (occurring in that order). It turns out that kinases regulate progress through the cell cycle, catalyzing timely protein phosphorylations. The first of these kinases to be discovered was mitosis-promoting factor (MPF). Kinase-regulated events are checkpoints a cell must pass through to enter the next phase of the cell cycle. As you might guess, the failure of a checkpoint can have serious consequences. One consequence is carcinogenesis, a runaway proliferation of cancer cells. We begin this chapter with a brief description of binary fission in E. coli, followed by a closer look at the eukaryotic cell cycle. We close with a look at alternate fates of eukaryotic cells and at details of cellular end-of-life events, including apoptosis, or programed cell death.
When you have mastered the information in this chapter, you should be able to:
1. Describe the phases of the cell cycle and what occurs in each.
2. Interpret experiments leading to our understanding of the separation of chromosomal events from duplication of the DNA contained in those chromosomes.
3. Describe the role of cyclin and cdk (cyclin-dependent kinases) in MPF.
4. Compare the roles of different cyclins and cdks in regulating the cell cycle.
5. Define cell-cycle checkpoints that monitor cell cycle activities.
6. Explain the molecular interactions between DNA damage, cell cycle checkpoints (arrest of the cell cycle if vital activities are blocked) and apoptosis.
7. State an hypotheses for how cell cycling errors can transform normal cells into cancer cells.
8. List some examples of apoptosis in humans and other organisms.
9. Compare and contrast examples of apoptosis and necrosis.
10. Formulate an hypothesis to account for the degradation of cyclin after mitosis.
11. Research and explain how different chemotherapeutic agents work and the biochemical or molecular basis of their side effects.