1. Section 6-2 The Cell Cycle

2. The Cell Cycle Describes the Life of a Eukaryotic Cell Cell division in eukaryotic cells is more complex than in prokaryotic cells because it involves dividing both the cytoplasm and the chromosomes inside the nucleus. Cell division in eukaryotic cells is more complex than in prokaryotic cells because it involves dividing both the cytoplasm and the chromosomes inside the nucleus. Also have to correctly rearrange organelles to form two properly functioning cells. Also have to correctly rearrange organelles to form two properly functioning cells.

3. The Cell Cycle The cell cycle is a repeating sequence of cellular growth and division during the life of an organism The cell cycle is a 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 – called interphase A cell spends 90% of its time in the first three phases of the cycle – called interphase The cell only enters the last two phases of the cell cycle if it is about to divide. The cell only enters the last two phases of the cell cycle if it is about to divide.

4. Five Phases of the Cell Cycle 1. First Growth Phase or G 1 During this phase, a cell grows rapidly and carries out its routine functions. During this phase, a cell grows rapidly and carries out its routine functions. This phase occupies the majority of most cell’s life. This phase occupies the majority of most cell’s life.

5. Five Phases of the Cell Cycle 2. Synthesis Phase or S The cell’s DNA is copied during this phase. The cell’s DNA is copied during this phase. At the end of this phase, each chromosome consists of two chromatids attached to the centromere. At the end of this phase, each chromosome consists of two chromatids attached to the centromere.

6. Five Phases of the Cell Cycle 3. Second Growth Phase or G 2 Preparations are made for the nucleus to divide. Preparations are made for the nucleus to divide. Microtubules are assembled and used to move the chromosomes during mitosis. Microtubules are assembled and used to move the chromosomes during mitosis.

7. Five Phases of the Cell Cycle 4. Mitosis Process during cell division in which the nucleus of a cell is divided into two nuclei. Process during cell division in which the 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. Each nucleus ends up with the same number and kinds of chromosomes as the original cell.

8. Five Phases of the Cell Cycle 5. Cytokinesis The process during cell division in which the cytoplasm divides.

9. The Cell Cycle

10. The Cell Cycle is Carefully Controlled How do cells know when to divide? How is the cell cycle controlled? Cells have a system that controls the phases of the cell cycle. Cells have a system that controls the phases of the cell cycle. Similar to a set of “red-light-green-light” switches that are regulated by feedback information from the cell. Similar to a set of “red-light-green-light” switches that are regulated by feedback information from the cell.

11. Has key checkpoints or inspection points at which feedback signals from the cell can trigger the next phase of the cell cycle (green light). Has key checkpoints or inspection points at which feedback signals from the cell can trigger the next phase of the cell cycle (green light). Other feedback signals can delay the next phase to allow for completion of the current phase (yellow or red light). Other feedback signals can delay the next phase to allow for completion of the current phase (yellow or red light). Controlled by proteins Controlled by proteins

12. Principle Checkpoints of the Cell Cycle 1. Cell Growth Checkpoint or G 1 Checkpoint  Makes the key decision of whether the cell will divide.  If the cell is healthy and large enough, proteins will stimulate the cell to begin the synthesis or S phase to copy the cell’s DNA.  If conditions aren’t favorable, cell can stop cycle at this phase.  Also will stop at this phase if cell needs to pass into a rest period. Some cells (muscle and nerve cells) remain in rest period permanently.

13. Principle Checkpoints of the Cell Cycle 2. DNA Synthesis Checkpoint or G 2 Checkpoint  DNA replication is checked at this point by DNA repair enzymes.  If checkpoint is passed, will trigger mitosis and cell begins many molecular processes needed to proceed into mitosis.

14. Principle Checkpoints of the Cell Cycle 3. Mitosis Checkpoint  This checkpoint triggers the exit from mitosis.  Signals the G 1 phase (major growth period of cell cycle)

15. When Control is Lost: Cancer Certain genes contain information necessary to make the proteins that regulate cell growth and division. Certain genes contain information necessary to make the proteins that regulate cell growth and division. If one of those genes are mutated, the protein may or may not function, and regulation of cell growth and division may be disrupted. If one of those genes are mutated, the protein may or may not function, and regulation of cell growth and division may be disrupted.

16. When Control is Lost: Cancer Cancer – the uncontrolled growth of cells Cancer – the uncontrolled growth of cells When proteins are disrupted, cancer may occur. When proteins are disrupted, cancer may occur. Essentially a cell division disorder Essentially a cell division disorder Cells do not respond to the body’s normal control mechanisms Cells do not respond to the body’s normal control mechanisms

17. When Control is Lost: Cancer Some mutations cause over-production of growth-promoting molecules, speeding up cell cycle Some mutations cause over-production of growth-promoting molecules, speeding up cell cycle Other mutations inactivate the proteins that slow or stop the cell cycle. Other mutations inactivate the proteins that slow or stop the cell cycle.

18. When Control is Lost: Cancer Mutations may occur spontaneously, but many occur due to environmental influences. Mutations may occur spontaneously, but many occur due to environmental influences. Many causes of cancer linked to lifestyle Many causes of cancer linked to lifestyle  Tobacco  UV radiation  Viruses  Diet?

19. Section 6-2 Summary There are 5 phases of the cell cycle: G1 phase, S phase, G2 phase, Mitosis, and Cytokinesis. There are 5 phases of the cell cycle: G1 phase, S phase, G2 phase, Mitosis, and Cytokinesis. There are three checkpoints to determine the phase the cell will enter. If the cell does not pass the checkpoint, it does not proceed into the next phase. There are three checkpoints to determine the phase the cell will enter. If the cell does not pass the checkpoint, it does not proceed into the next phase. Cancer is uncontrolled cell growth caused by mutations of the genes that control the cell cycle. Cancer is uncontrolled cell growth caused by mutations of the genes that control the cell cycle.

20. Section 6-2 Homework Review Questions Review Questions page 127 (1-4) STUDY FOR CHAPTER 6 VOCABULARY TEST!!!! STUDY FOR CHAPTER 6 VOCABULARY TEST!!!!