1. The Cell Cycle What is the cell cycle? What is mitosis – or cell division? What happens in each stage?

2. Cell Cycle Cells grow and dividedivide Why do you think cells need to stay relatively small?

3. Why can’t cells just keep growing and growing?

4. Most cells are small because Large cells place large demands on DNA – the DNA can’t “keep up” Large cells have trouble exchanging nutrients and wastes through the cell membrane – material has to travel too far

5. On the other hand… REALLY small cells like bacteria cells are not able to have specialized parts (organelles) bacteriabrain cell

6. The advantages of being larger (or multicellular) Can SPECIALIZE!!!

7. When will a cell divide? The surface area: volume ratio limits cell size. If a cell gets too big, it must divide to survive. If a cell gets too big, it will undergo mitosis.

8. Cell Cycle Interphase cell is growing and doing its thing Mitosis Cell division

9. Five Phases of the Cell Cycle G 1 – 1 st growth phase S – synthesis interphase G 2 – 2 nd growth phase M – mitosis C – cytokinesis division

10. Interphase - G 1 Stage 1 st growth stage 1 st growth stage Cell carries on normal activities Cell carries on normal activities

11. Interphase – S Stage Synthesis stage Synthesis stage DNA is copied DNA is copied Two identical copies of DNA Original DNA Why does the cell need 2 copies? What would happen if it did not have 2 copies?

12. Interphase – S Stage Why does the cell need 2 copies? What would happen if it did not have 2 copies when it got ready to divide?

13. Interphase – G 2 Stage 2 nd Growth Stage 2 nd Growth Stage Extra organelles & proteins are synthesized to prepare for division Extra organelles & proteins are synthesized to prepare for division

14. Mitosis: Division of the Nucleus Used for growth and repair Occurs in somatic (body) cells Produces two new cells identical to the parent

15. Mitosis – 4 stages P rophase P repare to divide M etaphase M iddle A naphase A part T elophase T he End http://www.cellsalive.com/mitosis.htm

16. Prophase DNA condenses to form visible chromosomes DNA condenses to form visible chromosomes Mitotic spindle forms Mitotic spindle forms Nuclear membrane dissolves Nuclear membrane dissolves

17. Metaphase Chromosomes line up at the equator (middle) Chromosomes line up at the equator (middle)

18. Anaphase Sister chromatids are pulled apart by spindle fibers Sister chromatids are pulled apart by spindle fibers

19. Telophase Sister chromatids at opposite poles Sister chromatids at opposite poles Spindle disassembles Spindle disassembles Nuclear envelope reforms Nuclear envelope reforms

20. Cytokinesis division of the cytoplasm division of the cytoplasm cell divides into two identical daughter cells cell divides into two identical daughter cells

21. What phase?

24. What stages?