1. Cell Growth and Division

2. Cell Growth Limits to growth Stress on DNA
Difficulty moving nutrients/wastes across membrane
Ratio of surface area to volume
Volume increases at a faster rate than surface area

3. Cell Division
Before a cell becomes too large, it divides, producing 2 daughter cells
Each daughter cell is an exact replica of the parent cell
Before the cell divides, the DNA is replicated, so each new cell will have the same genetic information as the parent cell

4. Cell Division 2 stages (eukaryotes)
Mitosis- division of the cell nucleus
Cytokinesis- division of the cytoplasm
Asexual reproduction (esp for unicellular organisms)
Also used for new cells as an organism grows and develops

5. Chromosomes
Threadlike structure within the nucleus containing the genetic information (DNA) that is passed from one generation of cells to the next
Cells of every organism have a specific number of chromosomes
Fruit flies = 8; Humans = 46; carrots = 18

6. Chromosomes
Chromatin- granular material visible within the nucleus; consists of DNA tightly coiled around proteins
Chromatid- one of two identical “sister” parts of a duplicated chromosome
Centromere- an area where the chromatids are attached to one another

8. The Cell Cycle
2 major phases
Interphase
Mitosis

9. Interphase 3 phases G1 phase= cells do most of their growing
Increase in size and synthesize new proteins and organelles
S phase= chromosomes are replicated and the synthesis and DNA molecules takes place
Usually if a cell enters S phase and begins replication, it completes the rest of the cycle
G2 phase= many of the organelles and molecules required for cell division are produced
Shortest of the 3 phases of interphase

10. Mitosis Divided into 4 phases Followed with Cytokinesis
Prophase
Metaphase
Anaphase
Telophase
Followed with Cytokinesis
Depending on cell- may last a few minutes to several days

11. Prophase 1st and longest phase of mitosis Events
Chromosomes become visible
Centrioles separate and move to opposite sides of the cell
Chromosomes become attached to fibers in the spindle at the centromere
Chromosomes coil more tightly
Nucleolus disappears
Nuclear envelope breaks down

12. Metaphase Often lasts only a few minutes Events
Chromosomes line up across the center of the cell
Microtubules connect the centromere of each chromosome to the two poles of the spindle

13. Anaphase Centromeres split
Sister chromatids separate and move to opposite poles
Anaphase ends when chromosomes stop moving

14. Telophase Chromosomes begin to disperse into a chromatin
Nuclear envelope re-forms around each cluster of chromosomes
Spindle begins to break apart
Nucleolus becomes visible

15. Cytokinesis Occurs at the same time as telophase Animal cells:
Cell membrane is drawn inward until the cytoplasm is pinched into 2 nearly equal parts
Plant cells:
Cell plate forms midway between the divided nuclei
Cell wall begins to appear in the cell plate
Result? 2 new identical cells

17. Controls on Cell Division
Effects of controlled cell growth can be seen by placing some cells in a petri dish containing nutrient broth
Cells grow until they form a thin layer covering the bottom of the dish
Cells stop growing when they come into contact with other cells
If cells are removed, the remaining cells will begin dividing again
Something can turn cell division on or off

18. Regulating Cell Growth
Cyclins- proteins that regulate the timing of the cell cycle in eukaryotic cells
Internal regulators: proteins that respond to events inside the cell
i.e. make sure all chromosomes have been replicated; make sure all chromosomes are attached to the spindle before entering anaphase
External regulators: proteins that respond to events outside the cell
i.e. embryonic development; wound healing

19. Uncontrolled Cell Growth
Cancer- disorder in which some of the body’s own cells lose the ability to control growth
Cancer cells do not respond to the signals that regulate the growth of most cells
P53 gene halts the cell cycle until all chromosomes have been properly replicated
A damaged or defective p53 gene causes the cells to lose the information needed to respond to signals that would normally control their growth