2. Cell Division Why do cells divide and what happens? Mitosis

3. Review Nucleus: - Control center of eukaryotic cells - Contains genetic information - Contains DNA in Chromosomes (dark rod-like/thread like structures seen in nucleus) - Determines characteristics (traits) of organisms

4. Somatic Cells -cells not involved in sexual reproduction -also called body cells Ex: skin cells, muscle cells, nerve cells, bone cells Why somatic cells divide: -Too big to supply needs of cell -Growth of organism -Develop (like an embryo) -Replace damaged/worn out cells -Heal wounds

5. Chromosome/Chromatin When a eukaryotic cell is not dividing, the DNA and associated proteins is a tangled mass of thin threads called chromatin. At the time of cell division, the chromatin condenses to form highly compacted structures called chromosomes. Chromatin chromosome

6. Chromosome Number Each species has a characteristic number of Chromosomes in their body cells: Humans: 46Cat: 38 Fruit fly: 8Catfish: 58 Broccoli: 18Dog: 78 Goldfish: 94Black Mulberry: 308 Mosquito: 6 King Crab: 208

7. Chromosome/Chromatid Just prior to mitosis, each chromosome duplicates to form sister chromatids Sister chromatids are genetically identical. A duplicated chromosome is made of two sister chromatids held together in a region called the centromere.

8. When the cells divide sister chromatids separate from one another. At the end of mitosis, each chromosome consists of a single chromatid.

9. DO NOW: How many chromosomes are in each of the four cells below?

10. Cell Cycle

11. Rate of Cell Cycle depends on the cell: - Fast: embryo - Fastest: skin, digestive tract - Don’t divide: muscle (heart) and nerve (brain) The Life Cycle of a cell Cells grow Then sometimes Reproduce

12. Interphase – - First stage of cell cycle (G 1, S, & G 2 ) - Longest part of the cell cycle - Nucleus and nucleolus clearly visible - Chromosomes not visible. - Not part of “Mitosis” G 1 = growth and activity S = chromosomes copied G 2 = final preparations for cell division

13. 1. Why does the nucleus enlarge during the S phase? 1. Why does the nucleus enlarge during the S phase? 2. If the cell meets all the criteria at each of its checkpoints, it finally enters the M phase. Describe what happens during this final stage of the cell cycle. 2. If the cell meets all the criteria at each of its checkpoints, it finally enters the M phase. Describe what happens during this final stage of the cell cycle. 3. Do all cells complete the cell cycle or go through it at the same rate? 3. Do all cells complete the cell cycle or go through it at the same rate?

14. Mitotic Phase Stage of the cell cycle when the cell is actually dividing. 2 stage process: 1. Mitosis – the nucleus divides and each daughter cell has identical number and types of chromosomes as the parent cell 2. Cytokinesis – cytoplasm divides

15. 4. Predict where in the cell cycle a neuron would remain throughout its lifetime. 4. Predict where in the cell cycle a neuron would remain throughout its lifetime.