1. The Cell Cycle

2. How do cells divide?
Cell division is a pattern of growth and division for the cell.
The cell will grow so that when it divides it will be the proper size and the new cell will have all of the “parts” that it needs.
Cells will continue to do this until they die

3. The cell cycle focuses on what happens in the nucleus……
The cell cycle focuses on what happens in the nucleus……. So lets first get to know the terms associated with our DNA.

4. Every cell has 6 feet of DNA inside its nucleus!
How much DNA is that?

5. How does the cell fit 6 ft of DNA in a nucleus?
The DNA is tightly packaged inside the nucleus.
We will see how this works on the next slide.

6. Chromatin:
DNA and proteins spread out loosely in the nucleus
Like a bowl of spaghetti

7. Duplicated Chromosome:
Long, rod-shaped structures composed tightly wound chromatin
Duplicated Chromosome:
Even when it is duplicated it is still considered a chromosome…..just duplicated
*Each arm is now called a sister chromatid held together at the centromere
*ONLY IN THIS STAGE WHEN THE CELL IS DIVIDING!

8. Chromosome Structure
Sister chromatids
centromere
chromatin

9. Chromosomes are formed from a single DNA strand that contains MANY genes
NOTE: Gene = a region of DNA that controls a hereditary characteristic (trait)

10. How many strands of DNA do we have in a normal body cell?
1 chromosome = 1-strand of DNA
How many strands of DNA do we have in a normal body cell? 46
Click for size perspective

11. Chromosomes Numbers
Every species has a set number of chromosomes in each cell
Humans have 46 chromosomes (23 pairs) in EVERY cell with the EXCEPTION of sex cells

12. Do you think that the number of chromosomes indicates how highly developed an organism is?
Check out other
organisms!

13. SEX CHROMOSOMES
chromosomes that determine the sex of an organism
Humans…Normal Female = XX Normal Male = XY
Chromosome pair #23
AUTOSOMES
All of the other chromosomes in an organism.
Chromosome pairs #ed 1-22

14. The two copies of each autosome are called HOMOLOGOUS CHROMOSOMES
Organisms receive one copy of each autosome from each parent and one of the sex chromosome
So we have 23 pairs!
One from mom and one from Dad
The two copies of each autosome are called HOMOLOGOUS CHROMOSOMES
Their “bands” line up!

15. HOMOLOGOUS CHROMOSOMES
= chromosomes of the same size, shape, and banding pattern. One chromosome of the pair came from each parent.
Their “bands” line up!

16. Haploid (1n) = cells that contain only ONE SET of chromosomes
(germ cells/sex cells/gametes)
Diploid (2n) = cells that contain
TWO SETS of chromosomes
(somatic cells / body cells)

17. When a sperm cell (1n) and an egg cell (1n) combine, the new cell will be diploid (2n)

18. Karyotype: A picture of the chromosomes in a dividing cell
Used to examine an individual’s chromosomes

19. KA R YO T YPE
Normal Male

20. Karyotype BEFORE Mitosis Karyotype AFTER Mitosis
Karyotype AFTER Mitosis

21. Haploid cell Diploid cell

23. Remember: How many chromosomes do humans have?

24. The Cell Cycle: Interphase and Mitosis
Mitosis is a process that helps organisms grow, develop, and heal. Mitosis refers to the division of “body cells.” Think My Toe

25. 2 main parts to the cell cycle
1. Interphase
2. Cell Division
(AKA--Mitotic Phase)

26. 1.
Cell Cycle:
Interphase
3-phases

27. INTERPHASE:
Period of cell growth and development that precedes mitosis and follows CYTOKINESIS (cell splitting)
Longest phase of the cell cycle
Centrioles

28. 3-stages of interphase
G1 = Growth 1—most cell growth (cell contents are duplicated)
S = Synthesis—DNA is duplicated
G2 = Growth 2—cell grow a little to prepare for division and “double checks” for errors

30. Cell Division (mitosis plus cytokinesis)2.
Cell Cycle:
Cell Division (mitosis plus cytokinesis)
4-phases

31. 1. PROPHASE:
Chromatin condense and thicken, now called chromosome. (DUPLICATED)
Nuclear envelope breaks down
Centrioles move to opposite "poles“ (or ends) of the cell

32. 2. METAPHASE: The spindle fibers (centriole) fully develops
The duplicated chromosomes align at the metaphase plate (middle)

33. 3. ANAPHASE:
Sister chromatids of the duplicated chromosomes separate and begin moving to opposite ends (poles) of the cell.
Spindle fibers lengthen and elongate the cell.
Each pole contains a complete set of chromosomes.

34. 4. TELOPHASE: Nucleus begins to form at opposite poles.
The nuclear envelopes and nucleoli also reappear.

35. Last event:
Cytokinesis

36. CYTOKINESIS:
= the division of the original cell's cytoplasm. (There are now two separate cells)

37. Cytokinesis: Animal Cell vs. Plant cell
Cleavage furrow forms and pinches cell in half.

38. Cytokinesis: Animal Cell vs. Plant cell
Cell plate forms to divide the cell.

39. MITOSIS CELL CYCLE Interphase Cell Division (Mitosis + Cytokinesis)
Prophase
Metaphase
Anaphase
Telophase
Interphase
Cell Division (Mitosis + Cytokinesis)

40. Overview of the Cell CycleG2 G1 S
Cytokinesis
Interphase
Cell
Division

41. Cell Cycle Regulation
Cell growth and division are carefully controlled.
Not all cells will go through the cell cycle at the same rate.
Examples of cells
rapidly dividing:
Examples of cells NOT dividing often:
Skin cells
RBC
Muscle cells
Nerve cells
Bone
marrow
/2009/05/red-blood-cells.bmp
_Cancer_(Non-Meloma)/The_Basics/Epidermis-dermis.jpg
Digestive
tract cells
cooper&part=A1967&rendertype=figure&id=A1982

42. Cell Cycle Regulation continued . . .
Cells that do not need to grow and divide can
enter G0 (resting) until they are needed.

43. Regulation Cells have both internal and external regulators.
Are all of the chromosomes attached
to spindle fibers and properly
aligned on the metaphase plate?
Internal regulators—are called cyclin and they make sure the cell is ready at certain checkpoints . . .
If not, the cycle stops (see diagram)
Is the cell
big enough?
Has all of the DNA duplicated completely or properly?
Is the cell big enough?

44. Guardian of the Genome
Tumor Suppressor Gene p53: anticancer function and plays a role in apoptosis, genomic stability, and inhibition of angiogenesis
Activates DNA Repair
Arrests Cell Cycle at G1/S checkpoint on DNA damage point
Activates apoptosis if DNA damage too severe
And more…
More than 50% of human tumors have mutation/deletion in p53 gene

45. Regulation continued . . . External regulators—
are called growth factors.
If cells are touching other cells = no growth
If space with no neighboring cells = grow/divide
Density-dependent inhibition

46. Cancer What happens if cells LOSE the
ability to CONTROL the cell cycle?
Cancer

47. Cancer Cancer = uncontrolled cell growth
. . . cancer cells do NOT respond to regulator signals
. . . results in masses of cells called tumors
. . . cancer = a disease of the cell cycle

48. Results in masses of cells called tumors –malignant vs. benign
Cancer:
Results in masses of cells called tumors –malignant vs. benign
Metastasize = travel

49. Meiosis: going from diploid to haploid
Making Gametes: Egg and Sperm

50. Cell Division with Meiosis
Where do your genes come from?

51. The cell cycle remains the same except…G1
Division: meiosis & cytokinesis S G2

52. A. Meiosis—Definition/Overview
Process of nuclear division that reduces the number of chromosomes in new cells to HALF the number in the original cell.
Diploid  Haploid

53. Female gamete = egg cell
Sex Cells (Gametes) are Haploid: ½ the genetic information!
Meiosis results in . . .
Sex Cells
Female gamete = egg cell
Male gamete = sperm cell
Images from:

54. A. Meiosis—Definition/Overview (continued)
Cells undergo all the phases of interphase
 Then they enter MEIOSIS which involves TWO distinct cell divisions
Division 1
Division 2
Image from:

55. Check Point Checkpoint: What happens during interphase?
Where in an organism’s body will cells carry out meiosis?

56. Meiosis I Prophase I (crossing over) Metaphase I
Anaphase I (homologous chromosomes separate)
Telophase I and cytokinesis

57. Prophase I
Prophase I is the longest and most complex phase.
All of the events that occurred during prophase of mitosis occur, PLUS…
Homologous chromosomes come together to form a SYNAPSE (TETRAD).
CROSSING-OVER occurs.

58. Crossing Over Crossing Over:
Portions of chromatids break off and attach to adjacent chromatids on the homologous chromosome
This allows for more genetic variability! We don’t want everyone to look the same.
Occurs during Prophase I

59. Metaphase I
Homologous chromosomes line up randomly at the center of the cell. We call this independent assortment.

60. Instead of all the chromosomes lining up in Metaphase in a single-file line, they will pair up with their homologous partner
Mitosis
Meiosis

61. Metaphase I

62. Anaphase I
During anaphase the homologous chromosomes in the center of the cell divide.

63. Telophase I / Cytokinesis
Telophase I two nuclei form (23 duplicated chromosomes in each)
Cytokinesis occurs resulting in 2 haploid daughter cells.

64. Meiosis I Interphase Prophase I Metaphase I Anaphase I Telophase I
Cytokinesis
Images from:

65. Meiosis II
Meiosis II comes directly after cytokinesis. No growth (interphase) takes place.
Meiosis II is broken into 4 events:
prophase II
metaphase II
anaphase II (sister chromatids separate)
telophase II and cytokinesis ( 4 haploid cells)
The steps of Meiosis II are identical to mitosis.

66. Prophase II Prophase II is the same as prophase in mitosis.
Chromatin condenses into chromosomes
Nuclear envelope breaks down

67. Metaphase II Metaphase II is the same as metaphase in mitosis.
Duplicated chromosomes line up in the middle of the cell
Spindle fibers from the centrioles attach to each sister chromatid

68. Anaphase II Anaphase II is the same as anaphase in mitosis.
Sister chromatids separate.

69. Telophase II Telophase II is the same as telophase in mitosis.
At the end of the second Cytokinesis in Meiosis there are 4 haploid cells
Males: 4 sperm
Females: 1 egg + 3 polar bodies

70. Meiosis II Coming from Meiosis I Prophase II Metaphase II Telophase II
Anaphase II
Cytokinesis
Images from:

71. Check Point Checkpoint: When did crossing over occur?
When do homologous chromosomes separate?
Why are sex cells haploid?
When do the sister chromatids separate?

72. C. Meiosis Summary Meiosis I = Meiosis II =
separates homologous chromosomes
Meiosis II =
separates sister chromatids
Image from:

73. What is the goal of meiosis?
Goals – reduce the chromosome number & mix up the DNA
Meiosis 2
Goals – separate sister chromatids and form 4 cells

74. Sister chromatids fail to separate properly during meiosis II
Error….
Non-
disjunction
Down Syndrome
(Trisomy 21)
Sister chromatids fail to separate properly during meiosis II

75. Non-disjunction: Klinefelters (XXY) and Turner Syndrome (X)

76. C. Meiosis Summary (continued)
At the end of meiosis II four UNIQUE daughter cells are produced (4 haploid cells)

77. Video: Amoeba Sisters Meiosis makes unique haploid cells.
As you study meiosis focus on two things:
How are we ‘mixing things up’ so that our offspring are unique?
How are we moving and separating the chromosomes so that we end up with ½ the material?