MYP Biology 5.3 Mitosis Notes

How Does a Cell Make Sure Each New Cell Gets the Same DNA?

1. Mitosis is the precise process that ensures accurate DNA copying and distribution.
2. This is key as any discrepancy will likely cause the cell to die or malfunction.

What Are the Stages of Mitosis?

1. Mitosis is divided into five distinct stages.
2. Each stage has specific events that must happen in order to successfully divide the cell.

1. Prophase

1. Chromosomes condense:
   1. They shorten and thicken through a coiling process.
   2. Each chromosome is a double structure because the DNA has been replicated.
   3. Chromosomes are still inside the nuclear membrane but becoming visible.
2. The spindle apparatus forms:
   1. Centrioles move to opposite poles of the cell (in animal cells).
   2. Spindle fibers begin forming between the poles.
3. The nuclear membrane breaks down:
   1. This allows spindle fibers to access the chromosomes.

2. Metaphase

1. Chromosomes line up at the center:
   1. The nuclear membrane has disappeared.
   2. Chromosomes are pulled into a line at the equator.
   3. Spindle fibers link the chromosomes to the poles of the cell.
   4. Each chromosome still contains two identical DNA molecules.

3. Anaphase

1. Chromosomes are pulled apart:
   1. Spindle fibers pull each chromosome apart.
   2. The identical DNA molecules separate and move to opposite poles.
   3. Each chromosome now contains just one DNA molecule.

4. Telophase

1. Nuclear membranes reform:
   1. Chromosomes reach the poles.
   2. Nuclear membranes form around each set of chromosomes.
   3. The DNA uncoils and spreads out.
   4. The cell can now divide into two identical cells.

5. Cytokinesis

1. The cytoplasm divides:
   1. In animal cells: A cleavage furrow forms and the membrane pinches inward until the cell splits.
   2. In plant cells: A cell plate forms down the middle, building new cell wall material until two cells are separated.
2. Two daughter cells are produced:
   1. Each has an identical nucleus with the same DNA.
   2. The cells are now in interphase where cell activities happen and the cells start to enlarge.

Note

• Although mitosis is an incredibly precise process, errors can slip through.
• When this happens, sometimes:
  • Both copies of a chromosome go to the same daughter cell (non-disjunction).
  • One cell ends up with an extra chromosome (Down Syndrome is caused by having an extra 21st chromosome)
  • Cells with wrong chromosome numbers usually die.