Download 05. Mitosis Handout

The Cell Cycle
Without cell division, living organisms cannot grow and develop. Each new cell must have a complete nucleus with a complete copy of all genetic instructions (DNA chromosomes).
As eukaryotic cells grow and divide, they move through three distinct stages. These stages make up what is known as the cell cycle. The stages of the cell cycle are interphase, mitosis, and cytokinesis. The length of time it takes to complete one cycle varies. Embryonic cells divide rapidly. Some of your body cells may take as much as 30 hours for a cycle. Very specialized cells, such as adult nerve cells may never divide at all. INTERPHASE
­­> Interphase is the longest stage for most cells, but it is not a resting stage. During interphase, the genetic material, DNA, is in very long, thin, invisible strands. When cell prepares for cell division, the strands are duplicated so that there are two identical copies of the genetic material. Cell Division
­cell division occurs in two stages: mitosis ­ the division of the contents of the nucleus ­ and cytokinesis ­ the division of the rest of the cell, such as cytoplasm, organelles, and cell membrane. Each cell division produces two genetically identical cells called daughter cells. ­Mitosis is composed of four phases:
1) prophase
2) metaphase
3) anaphase
4) telophase
­the cells move gradually from one phase to the next
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MITOSIS
1) Prophase
As interphase ends, the cell enters the first phase of mitosis ­ prophase. The long strands of DNA condense into a compact form, becoming visible under a light microscope as chromosomes. Because the DNA was copied during interphase, each chromosome consists of two identical strands called sister chromatids. An individual strand is called a chromatid. The sister chromatids are held together by a centromere. The nuclear membrane breaks down during prophase. 2) Metaphase
During metaphase, the chromosomes line up in the middle of the cell. This stage is easily recognized. All the chromosomes must be in the line for mitosis to continue
3) Anaphase
In anaphase, the centromere splits and the sister chromatids separate. They are now called "daughter chromosomes". These daughter chromosomes move to opposite sides of the cell. Under the microscope they appear to be pulled apart. 4) Telophase
Telophase is the final stage of mitosis. The daughter chromosomes stretch out, become thinner, and are no longer visible. A new nuclear membrane forms around each group of daughter chromosomes. At this stage, the cell appears to have two nuclei. CYTOKINESIS
Cytokinesis is the final stage of cell division. The cytoplasm divides, producing two genetically identical daughter cells. The process of cytokinesis is slightly different in plants and animal cells. In a plant cell, a plate between the daughter cells develops into a new cell wall. In an animal cell, the cell membrane is pinched off in the center. 2