The Cell Cycle

Why Do Cells Divide? Reproduce single celled organisms Repair Replace old cells Growth we all start out as a single cell…

Before Division… DNA must condense. How chromosomes form: Loose DNA = Chromatin Condensed DNA = Chromosome How chromosomes form: DNA wraps around proteins (histones), this continues to coil until condensed. DNA double helix DNA and histones Chromatin Supercoiled DNA

Chromosome Structure Chromatid = One half of a duplicated chromosome. centromere Chromatid = One half of a duplicated chromosome. Sister chromatids are held together at the centromere.

3 Stages of the Cell Cycle Interphase Mitosis Cytokinesis Did you know…Cell division may be as fast as 30 minutes (in some bacteria) or never (muscle, fat, nerve cells)

Interphase Longest phase of the cell cycle. DNA is uncoiled. 3 stages: Gap 1 (G1): cell growth, organelles replicate Synthesis (S): DNA is copied Gap 2 (G2): additional growth (prepare for mitosis)

Mitosis Division of the nucleus Has 4 stages Prophase Metaphase Anaphase Telophase Produces 2 genetically identical daughter nuclei. Occurs in somatic cells (all cells except sex cells)

Prophase Longest phase of mitosis. Chromosomes condense. Nuclear membrane dissolves. Centrioles move to opposite ends of the cell Spindle fibers form, attach to chromosomes.

Metaphase Chromosomes line up in the center of the cell.

Anaphase Sister chromatids separate, are pulled to opposite ends of the cell.

Telophase Spindle fibers disintegrate. Nuclear membrane forms. Chromosomes begin to uncoil.

Cytokinesis Cell pinches apart. In plant cells, a cell plate forms (will become the cell wall).

Cells divide at different rates. The rate of cell division varies with the needs of the cell.

Summary of the Cell Cycle Cats Summary of the Cell Cycle cat

Cell Cycle Tutorials Review: https://www.youtube.com/watch?v=JcZQkmooyPk Crash course: https://www.youtube.com/watch?v=L0k-enzoeOM http://www.youtube.com/watch?v=VGV3fv-uZYI (shows centrioles and spindle fibers well) Bozeman Science: http://www.youtube.com/watch?v=1cVZBV9tD-A

Practice Mitosis http://www.classzone.com/cz/books/bio_07/get_chapter_group.htm?cin=2&ci=5&rg=animated_biology&at=animated_biology&npos=1&spos=5&var=animated_biology (practice, click on mitosis stage matching)