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The Life of a Cell
As you grow, you pass through different stages in life. Your cells also pass through different stages in their life cycle. The life cycle of a cell is called the cell cycle.The cell cycle begins when the cell is formed and ends when the cell divides and forms new cells. Before a cell divides, it must make a copy of its deoxyribonucleic acid (DNA). DNA is the hereditarymaterial that controls all cell activities, including the making of new cells. The DNA of a cell is organized into structures called chromosomes. Copying chromosomes ensures that each new cell will be anexact copy of its parent cell. How does a cell make more cells? It depends on whether the cell is prokaryotic (with no nucleus) or eukaryotic (with a nucleus).
Making More Prokaryotic CellsProkaryotic cells are less complex than eukaryotic cells are. Bacteria, which are prokaryotes, have ribosomes and a single, circular DNA molecule but don’t have membrane-enclosed organelles. Cell division inbacteria is called binary fission, which means “splitting into two parts.” Binary fission results in two cells that each contain one copy of the circle of DNA. A few of the bacteria in Figure 1 areundergoing binary fission.
Eukaryotic Cells and Their DNA
Eukaryotic cells are more complex than prokaryotic cells are. The chromosomes of eukaryotic cells contain more DNA than those of prokaryoticcells do. Different kinds of eukaryotes have different numbers of chromosomes. More-complex eukaryotes do not necessarily have more chromosomes than simpler eukaryotes do. For example, fruit flieshave 8 chromosomes, potatoes have 48, and humans have 46. Figure 2 shows the 46 chromosomes of a human body cell lined up in pairs. These pairs are made up of similar chromosomes known as homologouschromosomes (hoh MAHL uh guhs KROH muh SOHMZ).
Making More Eukaryotic Cells
The eukaryotic cell cycle includes three stages. In the first stage, called interphase, the cell grows and copies its...