1. Cell Division and Mitosis
Ch. 5

2. God’s Command to Nature
Genesis 1
God created all living things and gave them a command: “Be fruitful and multiply, fill the earth and subdue it…”

3. There are FOUR main functions of Cell Division:
1. In unicellular organisms, cell division is the way these organisms reproduce.
The cell DIVIDES producing a duplicate or copy of itself

4. Cell Division
In multicellular organisms, cell division has several functions:
2. Regeneration- occurs when parts of organisms that have been damaged grow back or are replaced.
Ex. A starfish can grow a new arm if one is cut off.
Do you know of any other animals that can replace lost parts?

5. Cell Division
3. Healing- another function of cell division is the healing of wounds.
Whenever you have a cut or scrape on your skin, you can see the healing take place over a period of time.
While the wound heals, new cells are made through cell division to replace the destroyed and damaged cells.

6. Cell Division
4. A fourth important result of cell division is the growing process.
After a cell divides, both new cells grow and divide to form more new cells
Some cells can divide every few hours

7. Prokaryotic Cell Division
Bacterial cells reproduce by Binary Fission
Begins with DNA replication; each copy moves to opposite sides of cell
Followed by elongation of cell and replication of all internal cell parts, then split down the center between the two halves
Results in two cells that are identical versions (clones) of original cells

8. Binary Fission

9. Eukaryotic Cell Division
Two forms:
Mitosis
grow, replace dead or worn out cells, or to repair wounds
Asexual reproduction in fungi, protists, some plants/animals
Meiosis
Formation of gametes for sexual reproduction

10. The Cell Cycle
The length of time the cell cycle takes depends on the type of cell.
Usually the more specialized the cell the less likely it is to divide.

11. How often your cells regenerate?
Intestinal lining 2 to 30 days
Skin 21 to 30 days
Red blood cells 90 to 120 days
The pancreas 5 to 12 months
Muscles 6 months to 3 years
Tissues 1 to 7 years
Bones 8 months to 4 years
Nerve cells (in brain or from spinal cord) – after fetal development – never

12. Cell Cycle interphase G1 S telophase anaphase Mitosis G2 metaphase
prophase

13. The Cell Cycle: Interphase
When a cell is not dividing it is said to be in Interphase:
 G1: Gap 1, cells are recovering from an earlier cell division, synthesizing organelles and growing 
S: Synthesis, DNA replication occurs
G2: Gap 2, cells are making sure all the DNA was replicated correctly; a little more growth; the chromosomes start to undergo condensation, becoming tightly coiled; Centrioles replicate and one centriole moves to each pole.
G0: Cell has a specific job and does not divide

14. Interphase
interphase

15. DNA and Cell Division (Interphase)
During cell division, the genetic material DNA, needs to be copied and divided between the two new cells
DNA in cells is divided into long chains called chromosomes (“volumes” of DNA)
Chromosome DNA is wrapped around proteins called histones to organize it

16. Eukaryotic Chromosome Structure
Normally, chromosomes are spread out in a form called chromatin
During mitosis, chromatin folds up and condense to become chromosomes

17. Eukaryotic Chromosomes
sister chromatids: are 2 copies of the chromosome
The sister chromatids are bound together in the middle at a centromere

19. The Cell Cycle: Cell Division
Mitosis (M Phase)
Nuclear Division
Cytokinesis (C phase)
Cytoplasmic Division

20. Mitosis Video

21. Mitosis
Nuclear Division
Dividing up the genetic material (DNA)

22. Mitosis Mitosis is divided into 4 phases: 1. Prophase 2. Metaphase
3. Anaphase
4. Telophase

23. Mitosis
1. Prophase:
chromosomes condense and appear as sister chromatids joined at centromere
cytoskeleton disassembles
centrioles move to each pole of the cell; spindle apparatus is assembled
nuclear envelope dissolves

24. The Spindle Apparatus Moves chromosomes during mitosis
In both plant and animal cells, spindle fibers originate from centrosomes; in animal cells, centrosomes are called centrioles

25. Spindle Apparatus one spindle pole one of the condensed chromosomes
spindle equator
microtubules organized
as a spindle apparatus
one spindle pole

26. Prophase

27. Mitosis
2. Metaphase:
spindle fibers pull the chromosomes to align them at the middle of the cell called the metaphase plate

28. Metaphase

29. Mitosis
3. Anaphase:
- Spindle pulls sister chromatids away toward the poles

30. Anaphase

31. Mitosis 4. Telophase: spindle apparatus disassembles
nuclear envelope forms around each set of sister chromatids
chromosomes begin to uncoil
nucleolus reappears in each new nucleus

32. Telophase

33. Cytokinesis Division of the cytoplasm
Usually occurs between late anaphase and end of telophase
Two mechanisms
Cell plate formation (plants)
Cleavage furrow (non-plants or organisms without a cell wall)

34. Cytokinesis: Animal Cell
Cleavage furrow – is the pinching in of the cell membrane to divide the cell into 2 new cells

35. Cleavage Furrow

36. Cytokinesis: Plant Cells
Cell Plate Formation
In plant cells, a cell plate will form between the two dividing nuclei to form the new cell wall

38. Mitosis/Cytokinesis outcome
1 parent cell  2 identical daughter cells
Chromosome number remains the same from one generation to the next

39. Mitosis: plant vs. animal cells
Plant cell
Animal Cell
Centrioles
Absent
Present
Cytokinesis
Cell plate formation
Cleavage furrow

40. Control of the Cell Cycle
The cell cycle is controlled at three checkpoints:
1. G1/S checkpoint
-the cell “decides” to divide
2. G2/M checkpoint
-the cell makes a commitment to mitosis
3. late metaphase (spindle) checkpoint
-the cell ensures that all chromosomes are attached to the spindle

42. Control of the Cell Cycle
Proto-oncogenes:
-become oncogenes when mutated
-oncogenes can cause cancer when they are introduced into a cell