1. THE CELL CYCLE
and
CELL DIVISION

2. Think about it… why do cells stay small?
DNA Overload = Limit to Cell Growth
The information stored in that DNA is able to meet all of the cell’s needs in a small cell
If a cell grows too large, the DNA cannot produce enough proteins to supply the cell

3. CELL DIVISION
-before it becomes too large, a growing ‘parent’ cell divides into 2 ‘daughter’ cells
**Before cell division occurs, the cell replicates all of its DNA, one set/daughter
**2 main stages of eukaryotic cell division:
Mitosis – division of the cell nucleus
Cytokinesis – division of cell cytoplasm

4. Liver cell completes cell division – Magnification 11,500x

5. Chromosomes
Genetic information is passed from one generation to the next on chromosomes (made of DNA).
Chromosomes are only visible in most cells during cell division (other times, the DNA is in the not visible chromatin state)
Before cell division, the DNA condenses into compact structures, chromosomes

6. Chromosomes
Once copied, each chromosome consists of two identical “sister” chromatids.
Centromere –attachment
After cell division, each new cell receives one sister chromatid
Sister chromatids
Centromere

7. THE CELL CYCLE

8. The Cell Cycle During the cell cycle: a cell grows
prepares for division
divides
Interphase is the period of growth that occurs between cell divisions
-followed by mitosis and cytokinesis

9. The Cell Cycle

10. synthesizes proteins & organelles
increases in size
synthesizes proteins & organelles
chromosome replicated
DNA synthesis takes place
Enters S phase
completes cycle
organelles and molecules required for cell division are produced
Once G2 is complete, the cell is ready to start the M phase—Mitosis

11. Mitosis
The process of cell division which results in the production of two daughter cells from a single parent cell
The daughter cells are identical to one another and to the original parent cell.

12. Animated Cycle http://www.cellsalive.com/cell_cycle.htm

13. Mitosis
Prophase
Metaphase
Anaphase
Telophase

14. Chromosomes (paired chromatids)
Mitosis: PROPHASE
Spindle forming
Prophase
Chromosomes (paired chromatids)
Centromere
Most eukaryotic cells go through a regular cycle of interphase, mitosis and cytokinesis. Mitosis has four phases: Prophase, Metaphase, Anaphase and Telophase. The events shown here are typical of animal cells.

15. Prophase 1st & longest phase
Spindle
forming
Prophase
1st & longest phase
Centrioles separate and take up nuclear poles
Spindle, a microtubule structure, forms between the centrioles
Nuclear envelope breaks down.
Centromere
Chromosomes
(paired chromatids)

16. Mitosis: METAPHASE
Centriole
Spindle
Centriole
Metaphase

17. Metaphase The chromosomes line up across the center of the cell aka
Centriole
Metaphase
The chromosomes line up across the center of the cell aka
metaphase plate
Microtubules connect the centromeres to the fibers of the spindle.
Spindle

18. Individual chromosomes
Mitosis: ANAPHASE
Individual chromosomes
Anaphase

19. Anaphase Sister chromatids separate into individual chromosomes.
The chromosomes move and separate into two groups.
Individual
chromosomes

20. Nuclear envelope reforming
Mitosis: TELOPHASE
Nuclear envelope reforming
Telophase

21. Telophase
Chromosomes gather at opposite ends of the cell & lose their distinct shape
New nuclear envelopes forms around each cluster
Spindle breaks apart & nucleoli reappear

22. CYTOKINESIS
Cytokinesis

23. Cytokinesis Not a phase of mitosis
Cell membrane pinches in and the cytoplasm is split between the 2 cells
Each daughter cell has an identical set of duplicate chromosomes

24. Cytokinesis in Plants Cell plate
forms midway between the divided nuclei.
Cell plate
Cell wall

25. Animal Mitosis
Interphase                                                             
Prophase                                                             
Metaphase                                                             
Anaphase                                                             
Telophase                                                             

26. Plant Mitosis
Interphase                                                             
Prophase                                                             
Metaphase                                                             
Anaphase                                                             
Telophase                                                             

27. Cells in Mitosis
Things to look:
Shape of Cell & If there is a division forming between cells
Chromosomes & Location
Presence of a nucleus

28. Mitosis Animations http://www.johnkyrk.com/mitosis.html

29. Controls on Cell Division
Normal cells reproduce until they come into contact with other cells.
When cells come into contact with other cells, they respond by not growing.
This shows that cell growth and division can be turned on and off.

30. Cell Cycle Regulators Regulated by a specific protein called cyclin
Cyclin concentration rises and falls in time with the cell cycle
Internal Regulators:
-Proteins responding to events inside cell
- Allow the cell cycle to proceed only when certain processes have happened inside the cell.
External Regulators:
-Proteins responding to events outside cell
-direct cells to speed up/slow down the cell cycle

31. Cancer: Uncontrolled Cell Growth
cells lose the ability to control growth.
Cancer cells do not respond to the signals that regulate the growth of most cells.
Cancer cells divide uncontrollably and form masses of cells called tumors that can damage the surrounding tissues.
Metastasis-cancer cells may break loose from tumors and spread throughout the body

32. Cancer Cells

33. Interphase Plant Cell Animal Cell
Photographs from:

34. Prophase Plant Cell Animal Cell
Photographs from:

35. Metaphase Plant Cell Animal Cell
Photographs from:

36. Anaphase Plant Cell Animal Cell
Photographs from:

37. Telophase Plant Cell Animal Cell
Photographs from:

38. Meiosis
cell division by which germ cells (eggs and sperm) are produced.
One parent cell produces four daughter cells (not genetically identical)

39. During meiosis, DNA replicates once, but the nucleus divides twice.
Daughter cells have half the number of chromosomes (n=haploid) found in the original parent cell (2n=diploid)

40. Meiosis I
Prophase 1: Each chromosome duplicates and remains closely associated. These are called sister chromatids.
Metaphase 1: Chromosomes align at the center of the cell.
Anaphase 1: Chromosome pairs separate with sister chromatids remaining together.
Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the chromosome pair.

41. Prophase I

42. Prophase I

43. Metaphase I

44. Telophase I

45. 4 haploid daughter cells are formed
MEIOSIS II
Prophase 2: DNA does not replicate.
Metaphase 2: Chromosomes line up at the center of the cell
Anaphase 2: Centromeres divide and sister chromatids move separately to each pole
Telophase 2: Cell division is complete
4 haploid daughter cells are formed

46. Prophase II

47. Metaphase II

48. Telophase II

49. Meiosis

50. Meiosis Animation

51. Crossing Over
A section of 1 chromosome switches places with the same section from the other chromosome

53. Differences in Mitosis & Meiosis
Asexual
Cell divides once
Two daughter cells
Genetic information is identical
Meiosis
Sexual
Cell divides twice
Four haploid daughter cells
Genetic information is different

54. Purpose of Reproduction
To make sure a species can continue.
Definition: Reproduction is the process by which an organism produces others of its same kind.

55. Asexual Reproduction A new organism produced from 1 organism
The offspring will have hereditary material uniform with the hereditary material of the parent organism. This means they will be genetically alike.

56. Sexual Reproduction Requires two sex cells – egg and sperm
The egg and sperm join to form an entirely new organism
Different from the parent organism

57. IMPORTANT!
Asexual reproduction results in offspring that are genetically identical to the parent organism
Sexual reproduction results in offspring that are genetically different from the parent organisms-more energy so….
WHY IS IT WORTH IT?

58. Comparison Animations