1. Chapter 10:
Cell Growth and Division

2. Why do cells divide – why can’t they just grow bigger?
Surface area represents ability to take in/get rid of materials.
Volume represents needs of the cell – food, oxygen, water, etc.

3. Larger cube 2 mm tall
Surface area = 24 mm2
Volume = 8 mm3
Surface area to volume ratio = 3:1
Small cube 1 mm tall
Surface area = 6 mm2
Volume = 1 mm3
Surface area to volume ratio = 6:1

4. As a cell grows, the volume of the inside grows faster than the cell membrane around the outside
What happens when a cell gets too big?
It could starve – can’t take in enough food to support needs
It could poison itself – can’t get rid of waste fast enough
So cells stay small for exchange of materials

5. Rather than grow bigger, cells divide and increase in number
Cell division occurs when:
Body growth
Maintenance and repair
Fighting infection
Replacing worn/dead cells

6. Chromosome Structure
Chromatin – made of DNA and protein
Seen in a non-dividing cell
Chromosomes – Chromatin that has coiled tightly
Seen in a dividing cell
Histones – proteins that help to coil the DNA and maintain the shape of chromosomes

8. After replication, there are 2 identical sister chromatids, held together by a centromere

9. Eukaryotic Cell Cycle
A repeating sequence of cellular growth and division during the life of a cell.

10. Most of the cell cycle is spent in interphase (time between cell divisions):
G1 stage – cell growth and activity
S stage – DNA replication occurs (S stands for synthesis of DNA)
G2 stage – continues to grow and cell prepares for cell division

11. Amount of time spent in interphase varies – average for adult mammals is 20 hours
Nerve cells and muscle cells exit the cell cycle  G0 phase
Body never makes more of them

12. Following interphase is the M stage, including mitosis and cytokinesis
2 daughter cells are produced that are identical to the parent
Occurs in body cells
Diploid cells produce other diploid cells
Takes about 4 hours
Animation of mitosis

13. Mitosis overview

14. Centriole
Chromatin
Nucleolus (in yellow)
Nuclear membrane
Spindle fibers
Chromosome (replicated)
Centromere
Sister Chromatids (each half of replicated chromosomes)
Daughter Chromosomes (once the replicated chromosome splits)
Cell membrane
Cell membrane pinches in

22. Early Prophase
Chromatin coils to become chromosomes
Centrioles move to opposite ends of the cell
Nuclear membrane and nucleolus disappear

23. Late Prophase
Spindle fibers form
Chromosomes become attached to spindle fibers – centromere attaches to spindle fibers

24. Metaphase
Chromosomes line up at equator (middle)

25. Anaphase
Sister chromatids separate, becoming daughter chromosomes, and move toward opposite ends of cell

26. Telophase
Spindle fibers disappear
Nuclear membrane and nucleolus reappear
Chromosomes uncoil and turn back into chromatin

27. Cytokinesis, or division of cytoplasm, accompanies mitosis.
Division of the cytoplasm begins in anaphase, but is not completed until end of telophase.
In animal cell, cell membrane is flexible and pinches in to divide cell.
In plant cells, rigid cell wall does not bend, so a cell plate forms to divide the cell.

28. Mitosis in Plant Cells
Same phases as in animal cells
No centrioles
Cell plate forms instead of cell membrane pinching in

30. Cytokinesis in animal cells

31. Cytokinesis in plant cells

32. Cell Division in Prokaryotes
The process of asexual reproduction in prokaryotes is called binary fission.
The two daughter cells are identical to the original parent cell, each with a single chromosome.
Following DNA replication, the two resulting chromosomes separate as the cell elongates.
Cell divides without cell structures seen in plants & animals

33. Animation of binary fission