1. The Cell Cycle

2. Chromosomes DNA is packaged into chromosomes during cellular division
Number of chromosomes varies for every species
Humans have 46 in somatic cells; 23 in gametes

3. Chromosomes Chromosomes made of chromatin (DNA and protein)
Each chromosome made of one long linear DNA molecule with hundreds or thousands of genes
Proteins help to maintain structure of chromosome and control gene activities

4. The Cell Cycle The cell cycle consists of:
Interphase
G1, S, G2
Mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Most time is spent in interphase

5. The Cell Cycle

6. Interphase
Growth occurs and proteins and cytoplasmic organelles are produced throughout interphase
The synthesis or replication of DNA only occurs in the S phase

7. Prophase
Chromatin condenses into chromosomes. Each with a sister chromatid joined at the centromere.
Nucleoli disappears
Mitotic spindle forms
Centrosomes begin to move away from each other.

8. Prometaphase Nuclear envelope fragments
Microtubules extending from centrosomes can now enter nuclear area
Each chromatid now has a kinetochore at the centromere
Some microtubules attach to kinetochores; other nonkinetochore microtubules interact with other spindles

9. Metaphase Centrosomes at opposite poles
Centromeres/chromosomes line up at metaphase plate
Each kinetochore is attached to a microtubule (with sister chromatids attached to opposite sides)

10. Anaphase Shortest stage of mitosis
Cohesin proteins in sister chromatids are cleaved
Each chromosome begins movement to opposite pole as kinetochore microtubules shorten
Nonkinetochore microtubules lengthen causing the cell to elongate

11. Telophase 2 daughter nuclei form Nuclear envelopes arise
Nucleoli reappear
Chromosomes become less condensed
Mitosis (division of the nucleus) is complete

12. Cytokinesis Division of cytoplasm begins in telophase
In animal cells, cytokinesis involves a cleavage furrow which pinches the cell into two; plant cells use a cell plate which eventually becomes the cell wall

13. Binary Fission
Asexual reproduction of single celled eukaryotes and prokaryotes
Eukaryotic binary division involves mitosis, but prokaryotic binary fission does not

14. Control of the Cell Cycle
Checkpoints within the cell cycle control when particular stages will pause or when a cell will move to another phase
Checkpoints generally check to make sure that appropriate functions have occurred prior to moving forward

15. Control of the Cell Cycle
Protein kinases are enzymes that activate or inactivate other proteins by phosphorylation
Give the go ahead in G1 and G2 checkpoints
Cyclin is a protein whose concentration varies throughout the cell cycle
Attaches to cyclin dependent kinases to activate them (such as MPF)

16. Control of the Cell Cycle
Signals inside and outside the cell also play a role in cell division
Anaphase will not occur until all kinetochores are attached to spindle fibers
Cells will not divide in the absence of essential nutrients or, for most mammal cells, growth factors specific to the cell type
Density-dependent inhibition – crowded cells stop dividing (usually a single layer)
Anchorage dependence – cells must be attached to a substratum to divide

17. Loss of Control
Some cells do not abide by the controls set forth by the cell cycle and become cancer cells.
Normal cells divide times before apoptosis, but cancer cells continue dividing indefinitely

18. Loss of Control
Normal cells undergo transformation to become cancerous. Normally these are killed by the immune system, but they may escape detection.
If these cells remain at the original site, they are considered a benign tumor; however, if the cells begin to spread and metastasize, this is malignant

19. http://www. biology. arizona