Lecture 6: Cell Division

Reasons for Cell Division

In Cell Division Copies of the DNA Must Be Sent to Both New Cells

Genetic Blueprints for Cells Are Organized Into Chromosomes

Genetic Instructions are Organized Into Genes

Before a Cell Can Divide it Must Duplicate its Chromosomes

Chromosomes Must Be Tightly Packaged for Division

Mitosis is Used for Growth and Repair

Meiosis is Used for Sexual Reproduction

In Mitosis (and Meiosis) Chromosomes are Separated by the Spindle Apparatus

The Cell Division Cycle Has Five Stages:

Cancer is Uncontrolled Mitosis

Summary of Mitosis:

 

 
 Interphase: Duplication of DNA, organelles, proteins. Nucleolus present in nucleus. Chromosomes not visible.  Early Prophase: Chromosomes condense, become visible. Centrosome divides. Spindle starts to form between the centrosomes.

 
 Late Prophase: Spindle formed, with centro- somes at opposite poles. Nuclear membrane dissolves. Chromosomes start to attach to spindle at their centromeres.  Metaphase: Chromosomes line up on spindle in center of cell.

 Anaphase: Centromeres split apart. Then chromosomes move to towards centrosomes at opposite poles of cell.  Telophase/Cytokinesis: Nuclear membrane reforms. Cell pinches into 2 cells in animals. In plants a cell plate separates the 2 new cells.

More Information

San Diego State University has a good animated tutorial of the cell cycle and mitosis. You can control the speed of the movie by increasing or decreasing the frames per second.

The University of Arizona has good tutorials on both mitosis and meiosis. Test your knowledge of mitosis by identifying dividing onion root tip cells.

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