The Cell Cycle and Mitosis
X-ray of a broken radius (arm)
When large cells do not function efficiently, the cells divide. Cell division keeps cells from growing larger, and also produces new cells for the organism. You grew from a single fertilized cell (smaller than the period at the end of this sentence) to the large, multicellular organism you are today! Cell division is important to repair damaged cells. For example, if you break a bone, your bone cells will divide to produce new bone cells to repair the broken bone. This happens with skin cells too when you fall and scrape your knee.
The Cell Cycle - Interphase
The growth and division of eukaryotic cells is called the cell cycle, which is a process that occurs in stages. The first stage is called interphase. Interphase is further broken-down into the phases: Gap 1, Gap 0, Synthesis, and Gap 2. The phases of interphase are important in the creation of healthy cells, which are able to divide the second stage of the cycle, called mitosis. In this interactivity, learn about the first part of the cell cycle by investigating interphase. Click the player button to begin.
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Cancer
Sometimes the checkpoints in the Gap 1 and the Gap 2 phase of interphase fail, and the cell cycle continues unregulated. The result is cancer – the uncontrolled growth and division of cells. Cancer cells spend less time in interphase, which means that they spend more time dividing. This results in a large number of cancer cells that crowd out normal cells. If this process continues, it will kill an organism.
Cancer cells develop because of mutations, or changes in the DNA, that occur in the proteins that control the cell cycle. Environmental factors that cause the mutations to occur are called carcinogens. Some examples of environmental carcinogens include, but are not limited to, tobacco, secondhand smoke, ultraviolet radiation, asbestos, and some viruses and chemicals.
The Cell Cycle - Mitosis
Mitosis is the most complex of the cell cycle phases. During mitosis, the nucleus divides and each daughter cell receives a copy of the parent cell's chromosomes. Mitosis occurs in several phases, and is followed by the division of the cytoplasm, or cytokinesis. In this interactivity, explore the second part of the cell cycle by investigating mitosis and cytokinesis. Click the player button to begin.
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Time and Factors
The time it takes for cells to go through a complete cell cycle varies with the type of organism, type of cell, temperature, and the checkpoint control of the cell. For example, yeast cells can complete the cell cycle in 100 minutes with mitosis taking only 20 minutes. Chicken cells can complete the cell cycle in 8 hours with mitosis taking only 30 minutes. In humans, most cells can complete the cell cycle in 20-24 hours with mitosis taking 1 hour. In your lifetime, your body will undergo 10,000 trillion cellular divisions!
Binary Fission
Cell division is not unique to eukaryotic cells. Prokaryotic cells must also divide in order to create new cells. Mitosis does not occur in prokaryotic cells. Mitosis is the division of the nucleus, and prokaryotic cells do not have a nucleus. Prokaryotic cell divide by a process called binary fission. In this interactivity, learn about the three steps in binary fission. Click the player button to begin.
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The Cell Cycle Review
Now that you have learned about the cell cycle and mitosis, complete this activity to check your knowledge. In this non-graded interactivity, the information in the table is incorrect. Drag and drop the information found in the table into the correct row. Click the player button to get started.