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 -

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, copy DNA/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:

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:

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:

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:

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:

22. Animal Cell Mitosis
Interphase                                                             
Prophase                                                             
Metaphase                                                             
Anaphase                                                             
Telophase                                                             

23. Plant Cell Mitosis
Interphase                                                             
Prophase                                                             
Metaphase                                                             
Anaphase                                                             
Telophase                                                             

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.