The Cell Cycle and Asexual Reproduction (Mitosis)

1. The Cell Cycle and Asexual Reproduction (Mitosis) 1

2. How do little elephants grow up to be BIG elephants?

3. Why do animals shed their skin?

4. The Cell Cycle • Asexual reproduction in Eukaryotes is called the CELL CYCLE (Sometimes just called Mitosis) • Cell Cycle stages: G1, S, G2, and M • G1, S, and G2 are INTERPHASE • M is the division phase. It includes Mitosis (division of nucleus) and Cytokinesis (division of Cytoplasm) • Encompasses the entire life of the cell • Prokaryotes use a special cell cycle called “binary fission”

6. Purpose • Asexual reproduction – quickly make IDENTICAL offspring (clones) 2. Growth 3. Repair/Replace old cells Cell Cycle Animation - http://www.cellsalive.com/mitosis.htm

7. DNA • Every cell has at least one piece of DNA, but most have many pieces. The number depends on the species. (Ex: Humans have 46 pieces of DNA) • chromatin: uncoiled DNA ; easy to “read” (noodle DNA) • chromatid: single, coiled piece of DNA, ½ of a chromosome (dreadlock DNA) • chromosome: X-shaped pair of duplicated DNA pieces held together by a centromere(X DNA)

8. DIPLOID vs HAPLOID • Most cells are DIPLOID meaning two pieces of DNA per trait. • One piece from mom and one piece from dad. • Advantageous to be diploid because you have a BACKUP in case one piece is damaged. • These pieces code the same trait, but they may not be the exact same instructions. For example, one may say BLUE eyes while the other says BROWN. These means they are HOMOLOGOUS (same, but not EXACTLY the same) • Homologous pair: pair of “matching” chromosomes (one from each parent) that may have variations of the same trait (blue vs brown eyes) • Some cells do NOT contain pairs. They only have one piece of DNA for each trait, meaning they are half cells called HAPLOID (one DNA per trait, no pairs) • These cells are either simple (fungi) or used for sexual reproduction only • Note: Mitosis always makes DIPLOID cells. NORMAL (non-sex) cells are DIPLOID

9. Mitosis vs Meiosis • The purpose of Mitosis is to make DIPLOID, IDENTICAL cells • Later we will learn about Meiosis, which makes HAPLOID, VARIED cells for the purpose of sexual reproduction

10. Cell Cycle Stages

11. Interphase • Cell is doing its “day job” and maintaining homeostasis • G1 phase – grow/maintain homeostasis • S phase – synthesis, copyDNA/maintain homeostasis • G2 phase – prepare to divide/maintain homeostasis • Interphase is the longest phase of the cycle. It can last for hours, days, or even weeks. • Optional Phase – G0 phase: some cells enter G0 and NEVER divide; their “day job” is too important; ex: nerve cells (this is why spinal cord injuries do not heal) • Cell looks like a normal cell

12. Interphase (G1, S, and G2) Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

13. Mitosis – Prophase (prep) • Homeostasis is briefly paused for M phase; other cells will pick up the slack • Prophase is the first stage of M phase, aka mitosis • Cell prepares to divide by coiling the DNA into chromosomes and getting rid of the nucleus; spindle fibers form • Recognized by the visible chromosomes

14. Prophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

15. Mitosis – Metaphase (middle) • The coiled chromosomes line up single file in the middle attached to the spindle fibers • Recognized by the line of chromosomes in the MIDDLE

16. Metaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

17. Mitosis – Anaphase (apart) • Remember – each X shaped chromosome is made of DUPLICATED DNA! Each new cell will need ONLY one piece, so in anaphase… • The chromosomes are pulled apart by the spindles and dragged to opposite sides of the cell • Recognized by the APART

18. Anaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

19. Mitosis – Telophase (two) • Remember – mitosis only refers to the division of the NUCLEUS • Chromosomes uncoil, Two nuclei form around the DNA on the opposite sides; spindle disappears • Reverse of prophase • Recognized by the two visible nuclei

20. Cytokinesis (split cytoplasm) • This is NOT a part of mitosis! But it happens at the same time as telophase. • As telophase splits the nuclei, cytokinesis splits the rest of the cell • Animal cells – cleavage furrow (pinch the membrane until the cell splits • Plant cells – cell plate (new cell forms in between the two cells)

21. Telophase and Cytokinesis Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

22. Animal Cell Mitosis

23. Plant Cell Mitosis

24. What Phase?

25. What Phase?

26. What Phase?

27. What Phase?

28. Cancer • A mistake in mitosis leads to cancer • Cancer cells divide too fast and incorrectly. They take nutrients away from healthy cells and do not contribute to the body. • Any living thing with cells can get cancer. • We don’t know exactly what causes cancer, but damaging the DNA with things called carcinogens (e.g. UV rays, Xrays, smoking, alcohol, genetics) increases the chance of cancer • Cancer is hard to treat because anything that will kill cancer cells will also kill healthy cells.