Chapter 8 Cell Growth and Division

1. Chapter 8Cell Growth and Division Charles Page High School Stephen L. Cotton

2. Section 8.1 - Cell Growth • OBJECTIVES: • Describe cell growth.

3. Section 8.1 - Cell Growth • OBJECTIVES: • Define cell division.

4. Section 8.1 - Cell Growth • OBJECTIVES: • Relate cell growth to cell division.

5. Section 8.1 - Cell Growth • Remember that living things: • are made up of cells • grow, or increase in size • In most cases, a living thing grows because it produces more cells • An adult simply has more cells than an infant, not larger cells!

6. Section 8.1 - Cell Growth • Why more cells, and not larger cells? • Remember that materials enter and leave the cell membrane • How quickly this exchange occurs depends upon the surface area of the cell • But, how quickly food is used and wastes are made depends on the cell volume

7. Section 8.1 - Cell Growth • The cell’s volume grows faster than the surface area • If the diameter increases 10 times, the surface area increases 100 times, and the volume increases 1,000 times! • Figure 8-2, page 160

8. Section 8.1 - Cell Growth 1. The fact that the surface area and volume do not increase at the same rate creates problems for the cell • The larger cell will have a difficult time getting enough oxygen and nutrients in, and waste products out. • This is a reason why cells do not grow much larger, even though the organism can

9. Section 8.1 - Cell Growth 2. Another reason cells stay small is that the cell does not make enough DNA directions to make more protein • much like a town that has grown, but has not added a single book to their library- this results in an “information crisis” • CELL DIVISION solves the problem!

10. Section 8.1 - Cell Growth • Cell division- the process whereby the cell divides into two “daughter” cells • Most cells are about the same size, whether they come from an elephant or a mouse • Rates of cell growth? Some very fast- a E. coli can easily double it’s volume in about 30 minutes; then it divides.

11. Section 8.1 - Cell Growth • If they can divide this fast, why have they not taken over the world? • They quickly use up the available nutrient supply, and the rate of growth slows. • There are controls on cell growth: • certain places (heart, nerves) rarely ever divide • skin and digestive system divide often

12. Section 8.1 - Cell Growth • Some cells receive more “wear and tear”, thus they may need to be replaced often • The “controls” on growth can be turned on and off: • an injury such as a cut or broken bone causes cells at the injury site to be stimulated to divide rapidly • this slows as healing nears completion

13. Section 8.1 - Cell Growth • Uncontrolled cell growth can be severe • Cancer- cells have lost their ability to control their rate of growth; they continue to grow (for no apparent reason) until their supply of nutrients is exhausted

14. Section 8.2 - Cell Division: Mitosis and Cytokinesis • OBJECTIVES: • Define mitosis and cytokinesis.

15. Section 8.2 - Cell Division: Mitosis and Cytokinesis • OBJECTIVES: • Describe the cell cycle, and the changes that take place during interphase.

16. Section 8.2 - Cell Division: Mitosis and Cytokinesis • OBJECTIVES: • Discuss the events and the significance of mitosis.

17. Section 8.2 - Cell Division: Mitosis and Cytokinesis • The division of eukaryotic cells occurs in two main stages: 1. Mitosis- the process by which the nucleus divides into two nuclei, each with the same number and kinds of chromosomes as the parent cell

18. Section 8.2 - Cell Division: Mitosis and Cytokinesis • The division of eukaryotic cells occurs in two main stages: 2. Cytokinesis- the process by which the cytoplasm divides, thus forming two distinct cells. • Because eukaryotic cells are complex, the process of cell division is also complex; thus it is a delicate process.

19. Section 8.2 - Cell Division: Mitosis and Cytokinesis • CHROMOSOMES- are structures in the cell that contain the genetic information that is passed from one generation to the next • prokaryotic cells have chromosomes made up of long circular molecules of DNA • eukaryotic- made of distinct lengths

20. Section 8.2 - Cell Division: Mitosis and Cytokinesis • Each organism has a distinct number of chromosomes (Fig. 8-7, page 165) • humans have 46; goldfish have 94, etc. • Chromosomes are made of chromatin, which is made of DNA and protein • During early division, the chromatin condenses and the chromosomes become more visible.

21. Section 8.2 - Cell Division: Mitosis and Cytokinesis • Much of the protein is involved in folding the DNA to fit into the nucleus; and it is in the shape of a double helix • 1973, it was discovered that the chromosomes’ DNA was coiled around special proteins called histones • DNA + histones = beadlike structures called nucleosomes- form a thick fiber

22. Section 8.2 - Cell Division: Mitosis and Cytokinesis • Chromosome structure: • When the chromosomes are more visible, it is the start of mitosis • At this point, they contain two chromatids, attached to each other by a centromere (Fig. 8-9, page 166)

23. Section 8.2 - Cell Division: Mitosis and Cytokinesis • THE CELL CYCLE: • this is the period from the beginning of one mitosis to the beginning of the next • during this time, the cell grows, prepares for division, and divides into the two new daughter cells • it includes mitosis (the period of active division), interphase (a period of no division), as well as cytokinesis

24. Section 8.2 - Cell Division: Mitosis and Cytokinesis • THE CELL CYCLE (continued) • Mitosis is represented as the M phase, and this is when the nucleus divides • Interphase is divided into 3 phases: 1. G1 (gap 1) 2. S (DNA synthesis) 3. G2 (gap 2) • G1 and G2 -periods of growth/activity

25. Section 8.2 - Cell Division: Mitosis and Cytokinesis • THE CELL CYCLE(continued) • The time required to complete a cycle is the time required for it to reproduce itself, and not all cells move through the cycle at the same rate: • human muscle and nerve cells do not divide at all once they have developed • digestive linings grow/divide rapidly

26. Section 8.2 - Cell Division: Mitosis and Cytokinesis • INTERPHASE- this is the period between divisions, and can be quite long. The actual division takes place quickly. • G1 - (gap 1) - period of activity in which cell growth and development takes place • this is followed by the S phase

27. Section 8.2 - Cell Division: Mitosis and Cytokinesis • INTERPHASE(continued) • S phase - DNA synthesis. This is when the DNA is “replicated”, and several other proteins are synthesized. • This is the longest part of Interphase • G2 - (gap 2) - usually shortest time, involves the synthesis of organelles and materials for cell division

28. Section 8.2 - Cell Division: Mitosis and Cytokinesis • During interphase, the nucleus is active in synthesizing messenger RNA in order to direct cellular activities. • Although it seems to be a “quiet” phase (mainly growth), it is actually a period of intense activity. • Fig. 8-11, page 167

29. Section 8.2 - Cell Division: Mitosis and Cytokinesis • Mitosis (or the M phase) is the process of dividing the nucleus into two nuclei • may last anywhere from a few minutes to several days • Divided into 4 phases: 1) prophase, 2) metaphase, 3) anaphase, and 4) telophase

30. Section 8.2 - Cell Division: Mitosis and Cytokinesis 1. PROPHASE: • this is the longest phase of mitosis, often taking 50-60% of the time • first clue for prophase is that the chromosomes are beginning to appear distinctly (chromatids attached by a centromere)

31. Section 8.2 - Cell Division: Mitosis and Cytokinesis 1. PROPHASE: (continued) • centrioles separate, and position themselves at opposite sides of the cell (plants do not have centrioles) • the condensed chromosomes attach to the spindle (a mesh- like structure that helps move the chromosomes apart)

32. Section 8.2 - Cell Division: Mitosis and Cytokinesis 1. PROPHASE: (continued) • the centrioles and spindle are composed of the type of protein called microtubules • near the end of prophase, the nucleolus disappears, and the nuclear envelope breaks down • Fig. 8-12, page 168

33. Section 8.2 - Cell Division: Mitosis and Cytokinesis 2. METAPHASE: • as prophase ends, metaphase will automatically begin • this is the shortest time period, only lasting a few minutes • the chromosomes line up at the equator across the center of the cell • they connect to the spindle

34. Section 8.2 - Cell Division: Mitosis and Cytokinesis 2. METAPHASE: (continued) • the ends of the spindle are star-like structures called asters, which act like small “anchors” • Fig. 8-14, page 169

35. Section 8.2 - Cell Division: Mitosis and Cytokinesis 3. ANAPHASE: • this is the third phase of mitosis • the centromeres that join the chromatids split • the chromosomes repel each other to opposite sides of the cell • Fig. 8-15, page 169

36. Section 8.2 - Cell Division: Mitosis and Cytokinesis 4. TELOPHASE: • the final phase of mitosis • the chromosomes (which have been very distinct) now begin to coil together into a mass • nuclear envelope reforms • spindle breaks down

37. Section 8.2 - Cell Division: Mitosis and Cytokinesis 4. TELOPHASE: (continued) • the nucleolus becomes visible in each daughter cell nucleus • Fig. 8-16, page 170 • Mitosis is now complete; however, the process of cell division is not

38. Section 8.2 - Cell Division: Mitosis and Cytokinesis • CYTOKINESIS: • At this point, two nuclei (each with a duplicate set of chromosomes) are formed. • Now, we need to divide the cytoplasm (materials outside the nucleus) • cytokinesis- the division of the cytoplasm into two cells

39. Section 8.2 - Cell Division: Mitosis and Cytokinesis • CYTOKINESIS: (continued) • In animals, the cell membrane moves inward and pinches off • In plants, a structure called the cell plate forms midway between the divided nuclei; then a cell wall begins to appear in the cell plate • Fig. 8-17, page 170 • The cell now re-enters Interphase, and continues to grow and function.