Chapter 2, Section 3
Stage 2: Mitosis
Once interphase is complete, the second stage of the cell cycle begins. Mitosis (my toh sis) is the stage during which the cell’s nucleus divides into two new nuclei. During mitosis, one copy of the DNA is distributed into each of the two daughter cells.
Figure 10Bigger Pig, More Cells The mother pig has more cells in her body than her small piglets.
Scientists divide mitosis into four parts, or phases: prophase, metaphase, anaphase, and telophase. During prophase, the threadlike chromatin in the nucleus condenses to form double-rod structures called chromosomes. Each chromosome has two rods because the cell’s DNA has replicated, and each rod in a chromosome is an exact copy of the other. Each identical rod in a chromosome is called a chromatid. Notice in Figure 11 that the two chromatids are held together by a structure called a centromere.
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Figure 11Chromosomes During mitosis, the chromatin condenses to form chromosomes. Each chromosome consists of two identical strands, or chromatids. Applying Concepts During which phase of mitosis do the chromosomes form?
As the cell progresses through metaphase, anaphase, and telophase, the chromatids separate from each other and move to opposite ends of the cell. Then two nuclei form around the chromatids at the two ends of the cell.
Modeling Mitosis
Refer to Figure 12 as you carry out this activity.
Construct a model of a cell that has four chromosomes. Use a piece of construction paper to represent the cell. Use different-colored pipe cleaners to represent the chromosomes. Make sure that the chromosomes look like double rods.
Position the chromosomes in the cell where they would be during prophase.
Repeat Step 2 for metaphase, anaphase, and telophase.
Making Models How did the model help you understand the events of mitosis?
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Figure 12The Cell Cycle Cells undergo an orderly sequence of events as they grow and divide. The sequence shown here is a typical cell cycle in an animal cell. Comparing And Contrasting Compare the location of the chromosomes during metaphase and anaphase.
For: The Cell Cycle activity
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Length of the Cell Cycle
How long does it take for a cell to go through one cell cycle? It all depends on the cell. A human liver cell, for example, completes one cell cycle in about 22 hours, as shown in the graph. Study the graph and then answer the following questions.
(1) Reading Graphs What do the three curved arrows outside the circle represent?
(2) Reading Graphs In what stage of the cell cycle is the wedge representing growth?
(3) Interpreting Data In human liver cells, how long does it take DNA replication to occur?
(4) Drawing Conclusions In human liver cells, what stage in the cell cycle takes the longest time?
