1. Chapter 6 Section 2
The Cell Cycle
Grade 10 Biology
Fall 2010

2. Bell Ringer A typical eukaryotic cell spends 90% of its time in:
Mitosis
Anaphase
Interphase
Cytokinesis
What do you think a cell spends its life cycle doing?

3. Objectives
Identify the major events that characterize each of the 5 phases of the cell cycle
Describe how the cell cycle is controlled in eukaryotic cells
Relate the role of the cell cycle to the onset of cancer

4. The Life of a Eukaryotic Cell
Cell division in eukaryotes is more complex than in prokaryotes
Involves cytoplasm, chromosomes inside nucleus, and internal organelles

5. The Cell Cycle
Cell cycle: repeating sequence of cellular growth and division during the life of an organism
A cell spends 90% of its time in the first three phases of the cycle
Interphase
Only enters the last two phases of cycle if it’s about to divide

6. Cell Cycle

7. The Cell Cycle Phase #1: First growth (G1) phase
Cell grows rapidly and caries out routine functions
Occupies major portion of cells life
Cells that are not dividing remain in G1 phase
Most muscles and nerve cells never divide
If these cells die the body cannot replace them

8. The Cell Cycle Phase #2: Synthesis (S) phase Cell’s DNA is copied
At the end of the phase, each chromosomes consists of two chromatids attached at the centromere

9. The Cell Cycle Phase #3: Second growth (G2) phase
Preparations are made for the nucleus to divide
Hollow protein fibers called microtubules are rearranged during G2 in preparation for mitosis

10. The Cell Cycle Phase #4: Mitosis
Mitosis: nucleus of a cell is divided into two nuclei
Each nucleus ends up with the same number and kinds of chromosomes as the original cell

11. The Cell Cycle Phase #5: Cytokinesis
Cytkinesis: the process during cell division in which the cytoplasm divides

12. Cell Cycle

13. The Cell Cycle
Mitosis and cytokinesis produce new cells that are identical to the original cells
Allows organisms to grow, replace damaged tissues, and in some organisms reproduce asexually

14. Control of the Cell Cycle
How does a cell know when to divide?
Cells have a system that controls the phases of the cell cycle

15. Control of the Cell Cycle
Cell cycle as key checkpoints at which feedback signals from the cell can trigger the next phase of he cell cycle
Other feedbacks can delay the next phase
Cell cycle in eukaryotes us controlled by many proteins

16. Control of The Cell Cycle

17. Three Checkpoints Checkpoint #1: Cell growth (G1) checkpoint
Makes the decision of whether the cell will divide
If conditions favorable and cell is healthy and large enough, certain proteins will stimulate cell to begin synthesis (S) phase
S phase, cell copies DNA
If conditions are not favorable, cells can stop at this checkpoint
Cells can also stop at this check point if cell needs to go into resting period
Nerve, muscle cells

18. Control of the Cell Cycle
Checkpoint #2: DNA synthesis (G2) checkpoint
DNA replication is checked by DNA repair enzymes
If checkpoint passed, proteins trigger mitosis

19. Control of the Cell Cycle
Checkpoint #3: Mitosis checkpoint
Checkpoint triggers the exit of mitosis
Signals the beginning of the G1 phase, the major growth period of the cell

20. When Control is Lost Cancer
If gene that controls the proteins that regulate cell growth and division is mutated, protein may not function and regulation of cell growth and division can be disrupted
Cancer: the uncontrolled growth of cells, may result
Disorder of cell division
Cancer cells do not respond normally to body’s control mechanisms

21. When Control is Lost Some mutations cause cancer
Over producing growth-promoting molecules
Inactivating the control proteins that normaly act to slow or stop the cell cycle

22. Review
Differentiate between the G1, G2, and S phases of the eukaryotic cell cycle
Relate what occurs at each of the three principal check points in the cell cycle
Why are individual chromosomes more difficult to se during interphase than during mitosis ?
In the cell cycle of typical cancer cells, mutations have caused:
Slower growth
A failure in mitosis
Uncontrolled growth

23. Answers
G1: growth and development; S: DNA is copied; G2: preparations made for nucleus to divide
Checkpoint 1: makes decision if cell will divide; Checkpoint 2: DNA replication is checked, triggers mitosis; Checkpoint 3: checkpoint triggers exit from mitosis
Individual chromosomes are more difficult o se during interphae than in during mitosis because they haven't condensed and divided
C) uncontrolled growth