1. Cell Growth and Division
Chapter 5

2. Why do cells divide? (3 reasons)
DNA “Overload” – cells don’t have extra copies of DNA so large cells don’t have enough instructions
Inadequate Cell Surface Area
All materials must pass through membrane
Distance for diffusion
Large cells need more food; can’t absorb enough nutrients to maintain homeostasis
Surface area to volume ratio

3. Why do cells divide? 3. To become a multicellular organism
And later to replace worn out cells

4. How can the problem of “not enough surface area” be solved?

5. Series of steps to form two daughter cells
Cell Division:
Series of steps to form two daughter cells

6. Cell Division DNA must be replicated (copied)
Each piece of DNA  chromosome

7. Cell Division Identical copies of DNA  sister chromatids
Held together by a centromere
Chromosome

9. Series of events that cells go through as they grow and divide
Cell Cycle
Series of events that cells go through as they grow and divide

10. Four phases in the Cell Cycle
M phase
G2: doubles organelles
G1: growth of cell
S phase: DNA replication

11. Four Phases of the Cell Cycle
Mitosis:
Division of nucleus
Cytokinesis:
Division of the cytoplasm
G1, S, and G2: make up “Interphase”

12. Interphase 75% of cell’s life spent here “Inter” = between Centrioles
FYI:
Cannot see individual chromosomes during interphase
Nucleolus

14. Stages of Mitosis

15. Prophase First and longest phase of mitosis
Spindle Fibers
First and longest phase of mitosis
Chromosomes shorten and thicken (become visible)
Sister Chromatids

16. Prophase Nucleolus and nuclear membrane disappear
Centrioles move apart
Chromosomes attach to spindle fibers… push or pull chromosomes into middle

17. Metaphase Equatorial Plate Second and shortest phase
Chromosomes line up across the middle
Equatorial Plate
FYI: Chromosomes are at their shortest and thickest.

19. Anaphase Centromeres split
Sister chromatids pulled apart  now called chromosomes

21. Telophase Chromosomes Nuclear membrane reforms
reach poles, start to uncoil and lengthen
Nuclear membrane reforms
Spindle fibers break down
Nucleolus reappears
Two nuclei with same chromosomes

23. Cytokinesis Not a stage of mitosis Same time as telophase
Division of the cytoplasm and organelles

24. Cytokinesis Plant Cells Animal cells grows from middle
Called the cell plate
Animal cells
pinch inward – forms cleavage furrow

25. End Product of Mitosis:
Produces 2 identical diploid daughter cells
Same number of chromosomes (2N)

26. Rates of Cell Division Rapid Rarely Skin Digestive tract Bone marrow
Replace worn out or broken down cells
Rarely
Muscle
Nerve (slowest)
Stay in G0 phase – don’t grow or divide

27. Controlling Cell Growth
Stops growing when touching another cell
Can resume when space is found
This is called contact inhibition
Stops when can’t absorb enough nutrients
Cells can ignore signals to stop growing
Grow uncontrollably
Typical of cancer cells

28. Checkpoints M Checkpoint Attached to spindle fibers G2 Checkpoint
All organelles doubled
G1 Checkpoint
Checks for enough nutrients
Checks for DNA damage

29. What triggers the cell cycle?
Cyclin
protein that regulates cell division
Internal Regulators
External Regulators
From outside
Received by carbohydrate antennas
Transmitted to inside

30. Abnormal Cells Do not respond to signals May result in cancer
Caused by
Smoking (chemicals)
Radiation
Viral infections
Defect in the p53 gene that normally tells a cell to stop dividing

31. Unspecialized Cells Stem cells…stay in G0
Develop into any type of cells
Source-
bone marrow
umbilical cord blood
Embryonic cells
Potential uses:
Repairing spinal cord injuries
Repairing organs
Growing replacement parts