CELL GROWTH AND DIVISION

1. CELL GROWTH AND DIVISION Chapter 10, section 1

2. Limits to Cell Growth • There are two main reasons why cells divide rather than continuing to grow indefinitely. • The larger a cell becomes, the more demands are placed on its DNA • The cell has more trouble moving material into and out of the cell.

3. DNA “Overload” • When a cell is small, the information stored in DNA is able to meet all of the cell’s needs. • If a cell increases in size without limits, an information crisis would occur.

4. Compare a cell to a growing town: • In a small town, this main street is fine for a small population.

5. But imagine that the population grows, • The tiny street of the small town can no longer handle all of the people.

6. Exchanging Materials • In a cell, the rate at which oxygen and food enter a cell, and waste is removed from the cell depends on the total surface to volume ratio of a cell.

7. Ratio of Surface Area to Volume • Image a cell that is shaped like a cube. The cell has a length of 1 cm. • Surface area would be equal to length x width x number of sides, • Or, 1cm x 1cm x 6 = 6 cm squared.

8. The volume of the cell would be equal to: • Length x width x height • Or, 1 cm x 1 cm x 1 cm = 1 cm cubed. • The surface area by the volume ratio would be 6:1

10. If the cell size was doubled or tripled, the volume increases more rapidly than the surface area. • This makes it much more difficult to get materials into and out of the cell.

11. Division of a Cell • Before a cell becomes to large, a growing cell divides to form two “daughter” cells.

12. Before cell division occurs, the cell replicates, or copies, all of its DNA. • Each daughter cell is identical to the original.

13. CELL DIVISION Chapter 10, section 2

14. In eukaryotes, the first stage of cell division is called mitosis. • The second stage of cell division is called cytokinesis. • Reproduction by mitosis and cytokinesis is classified as asexual, because each new cell is identical to the parent.

15. Chromosomes • Chromosomes carry genetic information from one generation to the next. • Chromosomes are made up of DNA. • Humans have 46 chromosomes.

16. A chromotid is one of two “sister” parts of a duplicated chromosome. • Centomeres hold the chromatids together

17. The Cell Cycle • The cell cycle is a series of events that cells go through as they grow and divide. • During the cell cycle, a cell grows, prepares for division, and divides to form two identical daughter cells.

18. Events of the Cell Cycle • The cell cycle consists of four phases.

19. Interphase – is divided into three phases: • G1- During this stage, cells increase in size and make new proteins and organelles.

20. S – in this stage, chromosomes are replicated. • G2 – this is usually the shortest stage, many of the organelles and molecules required for cell division are produced.

22. Mitosis or the M phase • Biologists divide the events of mitosis into four phases: prophase, metaphase, anaphase, and telophase.

23. Prophase – chromosomes become visible. The centrioles, separate and take up positions on opposite sides of the nucleus.

24. Metaphase – chromosomes line up across the center of the cell.

25. Anaphase – chromatids are pulled apart by spindle fibers.

26. Telophase – chromosomes begin to disperse, the nuclear envelope reforms, and spindle fibers break apart.

27. Cytokinesis Cytokinesis is still part of the M phase. During cytokinesis, the cell membrane separates to form two identical new cells.