1. Cell Growth and Division:
Mitosis vs. Meiosis and What’s going on the rest of the time

2. Why does a cell need to divide?
A little geometry: As an object grows, the volume increases at a faster rate than the surface area

3. The same happens with a cell
What is the surface area?
What is the volume?
The more cytoplasm there is the more materials are needed.
How do the materials enter?

4. Oh no… diffusion is back!
By limiting the ratio of membrane to cytoplasm you limit the “doorways” into the cell.
Cell can’t get enough materials to support its large size
Cell dies, unless it divides in half!

5. What do our cells need to do before they can divide?
Get bigger
Make another copy of DNA
Make more organelles

6. Cell Cycle

7. Cell Cycle
G1 – growth and protein synthesis
S – DNA replication (copying the DNA)
G2 – Make organelles
M – Mitosis (Nuclear division) and
Cytokinesis – division of cytoplasm and membrane

8. What is DNA again? A Chain of nucleotides
Twisted into a double helix (spiral)
VERY LONG
Contains ALL the recipes for every protein our body needs
Recipes are called genes

9. Understanding DNA structure
Most of the time out DNA is in the form of chromatin: strings of DNA wrapped around proteins called histones

10. Understanding DNA structure
DNA is in chromatin form through G1.
In S phase, each strand of chromatin is duplicated and the duplicated copies remain attached together at the centromere.

11. Understanding DNA structure
During M phase the chromatin is folded into chromosomes
DNA remains in chromosome form until cell division is over

12. Understanding DNA structure

14. Remember DNA contains the information needed to build an organism
Each chromosome contains some of the information.
Each organism has a specific number of chromosomes.

15. Humans have 23 types of chromosomes and 2 of each type = total of 46 chromosomes
One of each type came from your mom the other from your dad.
Every cell in your body has all 46 chromosomes with the exception of egg/sperm cells

16. Cells that contain two of each chromosome are called Diploid cells
Cells that contain one of each chromosome are called Haploid cells

17. Think of the Information in a cell as an Encyclopedia
Chromosome Analogy
Think of the Information in a cell as an Encyclopedia
- Each chromosome is one book
Haploid = one set of info / one encyclopedia A B C D E

18. Diploid = two different sets of info/ two different encyclopedias!
Chromosome Analogy
Diploid = two different sets of info/ two different encyclopedias! A B C D E A B C D E

19. Genome = total information in cell
Chromosome Analogy
Genome = total information in cell
If a cell is haploid, the genome consists of all the information in one encyclopedia
If Diploid, all the info in both encyclopedias A B C D E A B C D E

20. Chromosome = One volume
Chromosome Analogy
Chromosome = One volume
Genes: segments of DNA; each contains a specific message
Genes are like Articles in encyclopedia A
F jkasdkfjh
Jadlfl he;
Kjadh fchw
Laksjdfh
Kasjdf;aj
Skdjfa;ie
F jkasdkfjh
Jadlfl he;
Kjadh fchw
Laksjdfh
Kasjdf;aj
Skdjfa;ie

21. Think of the alleles as two different articles on the aardvark!
Chromosome Analogy
Genes can have different variations. The variations are called Alleles.
Think of the alleles as two different articles on the aardvark! A
F jkasdkfjh
Jadlfl he;
Kjadh fchw
Laksjdfh
Kasjdf;aj
Skdjfa;ie
F jkasdkfjh
Jadlfl he;
Kjadh fchw
Laksjdfh
Kasjdf;aj
Skdjfa;ie

22. Chromosome Analogy
Homologous Chromosomes :
Contain same genes, but may contain different alleles
Example: both might contain Hair color gene but one might have brown hair info the other blonde
One from Mom, one from Dad

23. Homologous Chromosomes =
Chromosome Analogy
Homologous Chromosomes =
Volume “A” from each encycl. A A
Homologous Chromosomes

24. Chromosome Analogy
When DNA duplicates itself before cell division it makes two identical copies of each of chromosome
Identical Copies are Sister Chromatids
Sister Chromatids
Sister Chromatids A A A A

25. 1 duplicated chromosome, 2 sister chromatids
Single, unduplicated Chromosome
1 duplicated chromosome, 2 sister chromatids
2 separated chromatids become individual chromosomes

26. Centromere
Telomeres

27. Mitosis
One Fluid Event; no stopping and starting.
BUT: for ease of study, we break it into 4 stages
REMEMBER: all phases are continuous and may, in part, overlap

28. 1. Prophase
Longest phase of Mitosis
Chromatin folds up into Chromosomes which can now be seen

29. 1. Prophase
Centrosomes separate and move toward opposite poles
These are parts of the cell that make microtubules

30. 1. Prophase
Centrosomes start to form the Mitotic spindle
Made of microtubules

31. 1. Prophase
Nuclear membrane breaks down
Nucleolus disappears

32. 2. Metaphase
Chromosomes line up along equator
Spindle fibers attach to the centromeres of chromosomes

33. 3. Anaphase
Centromeres connecting sister chromatids separate and one chromatid of each chromosome moves toward each poles

34. 4. Telophase
Chromosomes begin to unwind back into chromatin
Nuclear Envelope reforms around chromosomes
Spindle breaks down
Nucleolus reappears

35. Cell Division is not yet Done!!
What have we made?
One Cell with Two complete Nuclei
What is left to do?
- Cytokinesis: Divide the cytoplasm and separate the cells

36. Cytokinesis
Animal cells: Membrane pinches inward forming a Cleavage Furrow until it divides the cytoplasm into two equal parts

37. Cytokinesis
Plant cell: Cell plate forms in the middle of the cytoplasm and extends toward the edges. Cell wall forms from this cell plate

38. Cell division is done!
Now you have Two Identical daughter cells

39. Controlling Cell Division
Cells know when they need to divide
When?
During growth
Repair – injury
Replacement (cells are not immortal!)

40. Controlling Cell Division
Cells know when they don’t need to divide
Cells stop when they reach other cells

41. How do cells “know”? Cells communicate by releasing molecules
To control cell division cells release proteins called “cyclins”
Some cyclins are “Go” signals
Trigger the cell division process
Some cyclins are “Stop” signals
shut down the cell division process

42. Loss of control
What happens if the control signals don’t work?!?
cells divide uncontrollably
Pile up on top of each other
Form big balls of cells called?????
TUMORS!!!

43. Tumors
Tumor cells do not respond to (or do not have) the body’s control signals
missing a “stop” signal so cell division doesn’t stop
Hyperactive “go” signal so cell is constantly dividing

44. Tumors Vs. Cancer
Tumor = uncontrolled but isolated growth of cells
Tumor cells become cancer when they start to invade healthy tissue
What if 1 cancer cell breaks off and enters the blood stream?
Where ever it “lands” = new tumor = metastasis

45. That’s how Somatic (or body) cells divide!
What would happen if we made Egg and Sperm cells this way?
Way too much DNA
What do we have to do when forming these cells?
Reduce the amount of DNA

46. Meiosis
Happens ONLY in sex cells
Reduces information by ½
Requires two different divisions
How many cells at the end??

47. Meiosis begins the same as Mitosis
Cell in G1 enters S phase.
ALL DNA is copied
Chromatin folds up to form 46 duplicated chromosomes

48. Meiosis I
Prophase I
- homologous chromosomes pair up forming tetrad; 4 chromatids together;

49. Meiosis I
Prophase I
- Centrosomes separate to poles
- Nuclear envelope breaks down

50. Meiosis I
Prophase I
- Crossing occurs between homologous chromosomes

52. Meiosis I
Metaphase I
- Spindle fibers attach to chromosomes at metaphase plate

53. - Fibers pull apart homologous chromosomes toward opposite poles
Meiosis I
Anaphase I
- Fibers pull apart homologous chromosomes toward opposite poles

54. Meiosis I
Anaphase I
- Fibers pull apart homologous chromosomes toward opposite poles

55. Meiosis I
Telophase I
- Two cells are formed (after cytokinesis)
- only half of the info of the Original cell
- 2N (diploid at start)  N (haploid at end of meiosis I)

56. Meiosis II
Prophase II
- Spindle reforms in each haploid daughter cell

57. Meiosis II
Metaphase II
- Chromosomes line up at the equator

58. Meiosis II
Anaphase II
- Sister chromatids are pulled to opposite poles

59. Meiosis II
Telophase II
- Four haploid (N) cells created

62. Compare and Contrast Mitosis and Meiosis