1. The Cell Cycle
Biology

2. Standards you are responsible for mastering.
SB1a: Explain the role of cell organelles for both prokaryotic and eukaryotic cells, including the cell membrane, in maintaining homeostasis and cell reproduction.
SB2b: Explain the role of DNA in storing and transmitting cellular information.

3. The next two slides aren’t for the notes…just pay attention.
A Question for you…
Cells need to be small.
That’s a fact.
But, WHY do they need to be small?
Why is it better to have many small cells than just a couple of big cells?

4. Ok, good.
So, how do organisms get more cells and prevent cells from getting too large??
Cell Division.

5. Two main reasons why cells divide:
1.) To prevent DNA overload  if the cell grows too big, there will be an information crisis.
2.) Bigger is not better if the cell grows too large, it would take too long for nutrients and wastes to travel through the cell.

6. Cell Division A.) the cell divides forming 2 daughter
cells before growing too big.
B.) solves the problems of:
1.) Information crisis
2.) Increasing size

7. Cell Division A.) Chromosomes: 1.) pass on genetic information
2.) made of DNA and proteins
3.) every organism has a specific number of chromosomes. (Humans = 46)
4.) are only visible during cell division
5.) are replicated BEFORE cell division
a.) chromatids  2 identical “sister”
parts of a duplicated chromosome.
1.) are attached at the centromere

8. Chromosome

9. Chromosome

10. The Cell Cycle 1.) The cell cycle is a series of events that
the cell goes through as it grows and
divides.
2.) During the cell cycle, the cell grows, prepares for division, and divides to form two daughter cells.

11. The 2 phases of the cell cycle
A.) Interphase
B.) Cell Division  Mitosis & cytokinesis

12. Interphase - NOT A PART OF MITOSIS; NOT CELL DIVISION!
1.) contains the G-1, S, and G-2 phases.
2.) G-1 phase  the cells grow in size and make new molecules and organelles.
3.) S phase  chromosomes are replicated
4.) G-2 phase  shortest phase, molecules & organelles needed for cell division are made.

13. Cell Cycle

14. Interphase

15. Interphase

16. Mitosis
1.) part of the cell cycle when the chromosomes separate from each other and the cell splits in half.
2.) This is how somatic cells reproduce.
Somatic cells are normal body cells (i.e., not sperm and egg)
3.) Mitosis has 4 phases:
Prophase - Nucleus breaks down, chromosomes become thick (visible) and pair up.
Metaphase - Chromosomes line up in the middle of the cell
Anaphase - Chromosomes move to the opposite ends of the cell
Telophase - Chromosomes unwind (become invisible) and nucleus reforms.

17. Prophase – more info…
1.) The chromatin condenses to form chromosomes (DNA is visible)
2.) Centrioles separate and the spindle fiber forms.
A.) spindle fiber  helps to separate the chromosomes.
3.) The nuclear envelope breaks down

18. Prophase

19. Prophase

20. Prophase

21. Prophase – Draw This in the Box…

22. Metaphase …more info
1.) Chromosomes line up at the equator of the cell.
2.) Each chromosome is connected to a spindle fiber at its centromere.

23. Metaphase

24. Metaphase

25. Metaphase

26. Metaphase – Draw this in the box

27. Anaphase …more info
1.) The sister chromatids separate into individual chromosomes and are moved to the opposite ends of the cell.

28. Anaphase

29. Anaphase

30. Anaphase

31. Anaphase – Draw this in the box…

32. Telophase…more info
1.) Chromosomes gather at opposite ends of the cell.
2.) chromosomes lose their shape
3.) Two new nuclear envelopes form.

33. Telophase

34. Telophase

35. Telophase

36. Telophase – Draw this in the box…

37. Cytokinesis - Starts during Telophase
1.) Cytoplasm divides separating the two identical nuclei.
2.) in animals  the cell membrane is pulled inward until the cytoplasm is pinched into 2 almost equal parts.
3.) in plants  a cell plate forms half way between the two new nuclei.

38. Animal Cell Cytokinesis
Cleavage furrow
Contractile ring of microfilaments
Daughter cells
100 µm
(a) Cleavage of an animal cell (SEM)
Figure 12.9 A

39. Plant cell cytokinesis
Daughter cells
1 µm
Vesicles forming cell plate
Wall of patent cell
Cell plate
New cell wall
(b) Cell plate formation in a plant cell (SEM)
Figure 12.9 B

40. End result of Mitosis
2 genetically identical daughter cells.

41. Review Questions

42. Review 1 During which part of interphase is the DNA copied? A.) G1
B.) S
C.) G2
D.) Mitosis

43. Review 2 Which stage in a cell’s life cycle is the longest?
A.) mitosis
B.) metaphase
C.) interphase
D.) cytokinesis

44. 3
Which of the following is the correct name of DNA when it is uncoiled (not in a chromosome form)?
A.) Chromatid
B.) Chromatin
C.) Chromosome
D.) Spindle Fiber

45. 4
If a cell has 32 chromosomes in G1 of interphase, how many chromosomes will each daughter cell have after mitosis & cytokinesis?
A.) 16
B.) 32
C.) 64
D.) 128

46. 5
During which stage of mitosis do the chromosomes line up at the equator of the cell?
A.) prophase
B.) metaphase
C.) anaphase
D.) telophase

47. 6 Each side of a copied chromosome is called: A.) a chromosome
B.) a sister chromatid
C.) chromatin
D.) centromere

48. 7
The part of a copied chromosome where the two sides are linked together is called the:
A.) centriole
B.) centromere
C.) chromatid
D.) spindle fiber

49. 8 During which stage of mitosis do the sister chromatids separate?
A.) prophase
B.) metaphase
C.) anaphase
D.) telophase

50. 9 Division of the nucleus is called: A.) interphase B.) cell cycle
C.) mitosis
D.) cytokinesis

51. 10 Division of the cytoplasm is called: A.) interphase B.) cell cycle
C.) mitosis
D.) cytokinesis

52. 11
What organelle has the job of pulling on the spindle fibers to separate the chromatids?
A.) DNA
B.) ribosome
C.) centromere
D.) centriole