Cell Division and Growth: DNA Control and Information Crisis

1. Chapter 10Cell Growth & DivisionSection 10-1 Cell Growth Read 1st Paragraph Fig. 10-1

2. Limits To Cell Growth • 2 reasons why cells divide rather than get larger. • They don’t have enough DNA. • They can’t move enough nutrients & wastes across the cell membrane.

3. DNA “Overload” • Remember: • DNA control’s cell function. • DNA is stored in the nucleus. • When a cell is small, the info in DNA is able to meet the cell’s needs. • But, as a cell increases in size, it doesn’t make more DNA. • If it were to keep growing, there would be an “Information Crisis”.

4. Cellular DNA

5. Compare the DNA in the nucleus to that of a small library. • Read P. 241 • Middle paragraph

6. Exchanging Materials • Recall that food, H2O, & O2pass through CM’s easily by passive & active transport. • Waste also leaves the cell through the cell membrane.

7. The rate at which these exchanges take place depends on the surface area of the cell. • Surface area =Total area of the cell membrane (CM). • However, the rate at which food & O2are taken in, & wastes produced depends on the cell’s volume. • Volume =How much space is in the cell.

8. Surface Area –Volume Ratio • Imagine a cell shaped like a cube. • p. 243, fig. 10-2 Follow along! • Important things to note: • Volume increases much faster than surface area. • This causes the surface area-volume ratio to decrease. • This causes serious problems for the cell.

9. http://plaza.ufl.edu/alallen/pgl/modules/rio/stingarees/module/why.htmlhttp://plaza.ufl.edu/alallen/pgl/modules/rio/stingarees/module/why.html

10. Surface Area to Volume Ratio Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume

11. Use the street –traffic analogy. • Read p. 242, bottom paragraph. • If a cell got too big, it would have trouble getting enough O2 & nutrients in, & waste out.

12. Division of the Cell • Before cells get too big they divide. • Division creates 2“daughter cells”. • This is called cell division. • Before cell division occurs, the cell copies its DNA. • This solves the problem of info shortages. • Cell division also solves the volume problem. • By reducing size, the cell reduces volume.

13. Cell Division

14. Section 10-2 Cell Division • Read p. 244 top paragraph • In prokaryotes (pro-k), cell division is just the splitting of the cell into 2 parts. • In eukaryotes(eu-k), cell division is complex & happens in 2 stages: • Mitosis • Cytokinesis

15. Prokaryotic Cell Division

16. Reproduction through mitosis is considered asexual. • All the cells are identical to the parent cell. • What are the resulting cells called?

17. Chromosomes • In eukaryotes, genetic info is carried by chromosomes. • Chromosomes are made of DNA & proteins. • Every org. has a certain # of chromosomes: Examples: • Fruit flies =8 • Carrot cells = 18 • Human cells = 46 • Dog = 78 • Sweet potato = 90

18. Chromosomes are normally visible only during cell division. • The rest of the time they are in a form known as chromatin. Before cell division happens, chromosomes are copied. For this reason, each chromosome consists of TWOidentical“sister”chromatids.See p. 244, Fig. 10-3

21. When cells divide, the “sister” chromatids separate from each other. • 1 chromatid goes to each of the 2 new cells.

22. Chromatids are held together by a centromere. • Normally located @ the middle of the chromatid • Some can lie near the ends. • A human cell contains 46 chromosomes (sometimes referred to as 23 pairs) • Each consisting of 2 chromatids.

23. The Cell Cycle • Cell cycle –series of events that cells go through as they grow & divide. • Interphase –period b/t cell divisions. • During each cell cycle: • A cell grows • Prepares for division • Divides to form 2 daughter cells • p. 245, fig. 10-4

24. TheCell Cycle G1 Consists of 4 phases: S • G1 Phase • S Phase • G2 Phase • M Phase G2

25. Events of the Cell Cycle • Most of a cell’s life is spent in interphase. • Interphase is divided into 3 phases: • G1 • Cells do most of their growing. • New proteins & organelles are also made. • S • Chromosomes are copied. • Synthesis of DNA molecules takes place. • G2 • Shortest of the 3 phases. • Organelles & molecules required for cell division are made. When the G2 phase is done, the cell is ready to enter the Mphase. a.k.a. = cell division

26. Mitosis • Divided into 4 phases: • Prophase • Metaphase • Anaphase • Telophase • Depending on the cell, mitosis can last from minutes to days. • PMAT

27. Prophase • 1st & longest phase. • Chromosomes become visible. • Centrioles separate & take up positions on opposite sides of the nucleus. Centrioles -2 tiny structures located near the nuclear envelope.

28. Spindle–a fanlike Microtubule structure that helps separatechromosomes. • Plant cells don’t have centrioles. • Near the end of prophase: • Chromosomes coil more tightly. • The nucleolus disappears. • The nuclear envelope breaks down.

29. Metaphase • 2nd phase • Often lasts only a few minutes. • Chromosomes line up at the midline or equator of the cell. • The centromeres of each chromosome connect to the spindle.

30. Anaphase • 3rd phase • During anaphase: • The centromeres joining the sister chromatids, separate & become individual chromosomes. • These chromosomes then move to opposite ends of the cell called poles. • Anaphase ends when the chromosomes stop moving.

31. Telophase • The 4th & final phase. • Chromosomes begin to disperse into a tangle of dense material. • The nuclear envelope reforms around the chromosomes. • The spindle breaks apart. • The nucleolus becomes • visible again.

33. M phase (Mitosis) Interphase G1 phase S phase G2 phase Prophase Metaphase Anaphase Telophase Cell Cycle includes is divided into is divided into

34. Interphase Prophase Metaphase Anaphase Telophase

36. Cytokinesis • Cytokinesis –the division of the cytoplasm. • Cytokinesis usually occurs at the same time as telophase. • It occurs in primarily 2 ways: • By pinching off b/t the 2 daughter cells equally. • Done in animal cells. • By building a cell plate b/t the 2 cells. • Done in plant cells.

38. Mitosis Video • http://www.johnkyrk.com/mitosis.html • https://www.youtube.com/watch?v=TlYqh5OfJFk

40. Section 10-3 Regulating the Cell Cycle

41. Note! • Not all cells move through the cell cycle at same rate. • Ex: • Muscle cells & nerve cells don’t divide at all, once they are developed. • Skin cells, digestive cells, & cells in bone marrow that make blood cells, divide rapidly throughout our life. • Rapidly dividing cells can pass through a cell cycle every few hrs.

43. Controls of Cell Divisionfig.10-7 • This illustration shows that cell division can be turned on & off. • The same thing happens when we have a cut in the skin or a broken bone. • New cells are made until the wound is healed, then they stop dividing.

44. Fig. 10-7 • Cells in a petri dish will continue to grow until they come into contact w/ other cells.

45. Cell Cycle Regulators • In the 1980’s, scientists discovered what controls the cell cycle. • The substance was a protein called cyclin. • Cyclin regulates the cell cycle. • Since this discovery, scientists have found other proteins that are involved in the cell cycle. • They call all these proteins cyclins. p. 251, fig. 10-8

46. Fig. 10-8 A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G2 of interphase. As a result, the second cell enters mitosis.

47. There are 2 types of regulatory proteins: Internal Regulators External Regulators

48. Internal Regulators • Made up of proteins that respond to events inside the cell. • Allows the cell to only proceed when certain events have happened. • Ex: • Cells wont move to the next phase in mitosis until all the right steps have been completed.

49. External Regulators • Made up of proteins that respond to events outside the cell. • They direct cells to speed up or slow down the cell cycle. • Important during wound healing & embryonic development.

50. Uncontrolled Cell Division • Cancer –a disorder in which some of the body's own cells lose the ability to control growth. • Cancer cells don’t respond to the signals that regulate the growth of most cells. • As a result they divide uncontrollably & form masses of cells called tumors. • Tumors can damage surrounding tissues. • Cancer cells can also move throughout the body & cause serious problems, or even death.