Binary fission
3.1
KEY IDEAS
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the cell cycle produces new cells from existing cells reproduction of prokaryotic cells occurs through binary fission.
The cell cycle
the production of new living organisms from other living organisms
cell cycle the process of a cell growing, dividing and dying
binary fission
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Binary fission
Prokaryotes (bacteria) have a single circular DNA molecule that carries their genetic material. Copying this DNA is the first step in the cell division that is called binary fission (Figure 1). During binary fission, a cell grows to almost twice its size before splitting into two equal-sized daughter cells. Prokaryotes do not have a nucleus, so their genetic material is located in the cytoplasm of the cell. The DNA that makes up a prokaryote’s genetic material is more than 500 times longer than the cell. To fit inside the cell, the DNA molecule is tightly wound around proteins to form a chromosome. When the prokaryote replicates, the DNA molecule FIGURE 1 Binary fission occurs when a cell unwinds to make a single copy of itself. divides into two equal-sized daughter cells. Here, Paramecium aurelia is going through binary fission. Each copy of DNA then attaches to a different part of the cellular membrane. As the cell grows longer (elongates), the two chromosomes are pulled apart. Once the elongated cell is large enough, the plasma membrane pinches in the centre, dividing the bacterial cell in half. A new cell wall forms around the two genetically identical daughter cells (Figure 2).
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a form of asexual reproduction in which the parent cell splits into two equal-sized daughter cells
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biogenesis
All cells come from pre-existing cells (biogenesis). Single-celled organisms reproduce through the process of cell division. Multicellular organisms grow from the division of a single cell (a fertilised egg), which continues to divide and grow to become a whole organism. This process needs to continue throughout a multicellular organism’s life to maintain normal day-to-day function, growth and repair. An example of this is the constant production of red blood cells by the stem cells in your bone marrow. The process of cell division is an important part of the cell cycle, from the first time a cell is formed from the division of its parent cell, until its own division to produce two new daughter cells. For division to be successful, each daughter cell must be genetically identical to its parent. This means the DNA of each parent cell must first make a copy of itself before the cell can divide into two.
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It is important to describe daughter cells as ‘genetically identical to the parent cell’ rather than ‘identical to the parent cell’. This is because the daughter cells may have different numbers of individual organelles from the parent cell or other daughter cells and so are not completely identical.
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Study tip
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In this topic, you will learn that: ✚
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BIOLOGY FOR VCE UNITS 1 & 2
OXFORD UNIVERSITY PRESS
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