Cell Growth and Division

1. Dr. Donna Howell Biology I Blacksburg High School Cell Growth and Division Chapter 10

2. Why Do Cells Divide? • Cells cannot grow forever. • There is a limit to their size. • Two reasons why they divide: • Larger cell = more demands on DNA • Larger cell = more trouble moving substances across cell membrane

3. DNA “Overload” • If a cell continued to grow, but the amount of DNA stayed the same, there would not be enough information in the DNA to control the whole cell.

4. Exchanging Materials • The rate at which cell products are used and waste is eliminated is related to cell volume. • There must be a certain ratio of surface area to volume for the cell to function efficiently.

5. Cell Division • Cell division is the process by which a cell divides into two new daughter cells. • Before division occurs, the cell makes copies of its DNA for the new cells.

6. Cell Division • There are two parts to cell division: • Mitosis – this is division of the cell nucleus. • Cytokinesis – this is division of the cytoplasm.

7. Chromosomes • Chromosomes are found in the nucleus of the cell, and contain DNA. • Human beings each have 46 chromosomes in their cells.

8. The Cell Cycle • The cell cycle is a series of events that cells go through as they grow and divide. • One cycle consists of a cell growing, preparing for division, and division into two daughter cells.

9. G1 Phase • The G1 phase of the cell cycle is the first phase, and it is where cells grow.

10. S Phase • The S phase is the second phase, and it is where the DNA is replicated (copied).

11. G2 Phase • The G2 phase is where the cell produces many of the organelles and molecules required for the new cells.

12. Mitosis • The next phase is mitosis, and this is where the actual cell division occurs.

13. Mitosis • There are four parts of mitosis: • Prophase • Metaphase • Anaphase • Telophase

14. Mitosis - Prophase • Chromosomes become visible • Centrioles take up positions on opposite sides of nucleus. • Spindle fibers formed. • Chromosomes coil more tightly. • Nucleolus disappears. • Nuclear envelope breaks down.

15. Mitosis - Metaphase • Chromosomes line up across the center of the cell. • Center part of chromosome connected to the two poles of the spindle.

16. Mitosis - Anaphase • Centromeres that join sister chromatids separate each chromosome in two.

17. Mitosis - Telophase • Chromosomes break down into tangle of material. • Nuclear envelope re-forms. • Spindle breaks down; nucleolus re-forms.

18. Cytokinesis • This is where the cell divides the cytoplasm into two equal parts.

19. Controls on Cell Division • Cell division can be speeded up or slowed down depending on the needs of the body. • A protein called a “cyclin” is what controls this.

20. Uncontrolled Cell Growth • Some cells, such as cancer cells, do no respond to the signals that require the growth of most cells. • As a result, they divide uncontrollably and form masses of cells called tumors.

21. What Causes Cancer? • Harmful substances, such as tobacco, radiation exposure, viral infections, or other causes not yet identified.

22. Where Do Cells Come From? • All cells in your body come from stem cells. • Stem cells are unspecialized cells that have the potential to become any other type of cell. • Stem cells can be used to regenerate cells that have been damaged in some way.

23. The End.