1. Cell Division Objectives 1. Describe the cell cycle. 2. Describe the events in each stage of mitosis. 3. Explain cancer as a disease of the cell cycle. Pg 240-252

2. Think! Think!! Think!!! Does a living thing grow larger because it increases the size of its cells or because it produces more cells?

3. Think! Think!! Think!!! Living things grow because they produce more cells. There is a limit to the size that cells can grow. The DNA that is in the nucleus of each cell is like the library of a small town. When the town is small, there are enough books for the residents to share. If the town population were to increase, there would be a shortage of books. So instead of growing larger, cells must reproduce.

4. Cell Division Cell Division – the process by which a cell divides into two new identical daughter cells Before cell division, the DNA of the cell is copied, so each daughter cell gets a copy. DNA – (deoxyribonucleic acid) the large molecule in the nucleus of each cell that carries genetic information

5. Chromatin Chromatin - DNA in the nucleus that looks like spread out “strings” when the cell is not dividing

6. Chromosomes Chromosomes – condensed chromatin visible in the nucleus when the cell is dividing Humans have 46 chromosomes or 23 pairs.

7. Chromosomes Before cell division, each chromosome is duplicated. The identical chromosomes attach to each other. Sister Chromatids – two identical chromosomes attached to each other Centromere – the place that the sister chromatids are attached to each other

8. The Cell Cycle Interphase G1 – “G for Grow” the cell size increases S – “S for DNA Synthesis” the chromosomes are duplicated G2 – centrioles and other organelles required for cell division are made Mitosis – the duplicated chromosomes separate, has four phases Cytokinesis – the cell physically splits in two

9. Cancer: A Disease of the Cell Cycle Cancer – a disorder in which some of the body’s cells divide uncontrollably. The cells that continue to divide cause masses called tumors. Causes can be tobacco, UV radiation, or viruses.

10. Mitosis Prophase – chromatin condenses into sister chromatids, centrioles separate, spindle forms, nuclear envelope breaks down Metaphase – sister chromatids line up across middle of cell, each is connected to a spindle fiber at its centromere Anaphase – sister chromatids separate and move to opposite sides of the cell Telophase – sister chromatids lose their shape and become chromatin, two new nuclear envelopes form http://www.rattlerscie nce.com/life/classes/p reapbio/documents/U nit%203/chapter10/ce ll_cycle.swf http://bio.rutgers.edu/ ~gb101/lab2_mitosis/ graphics/aavideo.mov