1. Chapter 10: Cell Division and Growth

2. Chromosomes
When cells are NOT dividing, DNA is found in the nucleus in the form of uncoiled chromatin.
What does this look like?

3. Chromosomes
When the cell is getting ready to divide, chromosomes form as the DNA wraps and coils tightly around histones.

4. Chromosomes
Chromosomes: carriers of genetic information that is copied and passed to new cells
Genes: section of DNA that controls production of a protein; found on a chromosome

5. Chromosomes Structure of Chromosomes
Sister Chromatids: two identical halves of the chromosome (made when DNA copies itself)
Centromere: middle area where two chromatids are joined

6. Non-replicated Replicated Centromere ONE chromosome chromosomes
Sister chromatids
ONE chromosome

7. Chromosomes Chromosome Numbers
Each species have a characteristic number of chromosomes
Fruit Flies = 8 chromosomes (4 pairs)
Adder’s Tongue Fern = 1, 263 chromosomes (631 pairs)
Humans = 46 chromosomes (23 pairs)

8. Chromosomes - Karyotype

9. Chromosomes TWO Types of Chromosomes
1. Sex Chromosomes: determine the sex of an organism
Humans have 2 of these chromosomes (1 pair)
Males: XY
Females XX

10. Chromosomes TWO Types of Chromosomes
2. Autosomes: remaining body chromosomes
Humans have 44 of these chromosomes (22 pairs) that “travel” in pairs

11. Chromosomes
Homologous chromosomes: two chromosomes in a pair; 1 copy from each parent
You have 2 of every chromosome that carry genes for the same trait, but they are NOT identical
Ex: Chromosome 19 contains genes for hair color
Mom’s #19 could have the “blonde” hair gene
Dad’s #19 could have the “brown” hair gene

12. b B C D E F a A c d e f The letters are the genes
Upper case and lower case letters are versions of the genes

13. Chromosomes Chromosomes in each cell
Diploid: a cell containing two copies of each chromosomes (both chromosomes in the homologous pair)
Abbreviated: 2N
Human Ex: skin cell, muscle cell (any BODY cell) 2N = 46

14. Chromosomes Chromosomes in each cell
Haploid: a cell containing one copy of each chromosomes
Abbreviated: N
Human Ex: Sperm & Egg cells (any SEX/gamete cell); N =23

15. Cell Size Limits Organisms grow by producing more cells
Cell size is usually comparable between a young and old animal; the older animal just has MORE of them

16. Cell Size Limits Why can’t cells continually grow larger?
DNA “Overload”: it can’t meet all the cells needs/demands

17. Cell Size Limits Why can’t cells continually grow larger?
Exchanging Materials:
Rate at which materials are exchanged depends on the cell membrane (surface area of the cell)
Rate at which materials are used (oxygen, water) or produced (waste) depends on the volume of the cell

18. Cell Size Limits
As the length of the cell increases, the volume increases faster than the surface area
Hard for cells to keep up with moving materials and wastes in and out so the cell divides

19. Cell Division in Eukaryotes
TWO types of cell division
1. Mitosis: Cell division that produced body cells identical to the original parent cell (diploid)
Examples of cells that do this: skin, muscle, heart
2. Meiosis: Cell division that produces gametes with half the number of chromosomes as the parent cell (haploid)
Ex of cells that do this: sperm and egg; GAMETES ONLY

20. Cell Division in Eukaryotes
Cell Cycle: sequences of growth and division of the cell
THREE STEPS OF THE CELL CYCLE
1. Interphase (most time spent here)
2. Mitosis
3. Cytokinesis

21. Cell Division in Eukaryotes
How long does it take for a cell to go through one cell cycle?
It all depends on the cell.
A human liver cell, for example, completes one cell cycle in about 22 hours, as shown in the graph.

22. Cell Division in Eukaryotes
1. Interphase: time when the cell is NOT dividing
THREE PHASES OF INTERPHASE
1. G1 = cell grows, makes organelles
2. S = DNA copied
3. G2 = cell makes centrioles; normal metabolism preparing to divide

23. Cell Division in Eukaryotes
2. Mitosis: dividing of the cell’s nucleus
FOUR PHASES OF MITOSIS
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

24. Cell Division in Eukaryotes
1. Prophase: longest phase of mitosis
Chromatin coils into visible chromosomes (sister chromatids)
Nuclear envelope/membrane starts to disappear
Spindle fibers appear from centrioles (animal cells only)

25. Cell Division in Eukaryotes
2. Metaphase: shortest phase of mitosis
Spindles attach and move chromosomes to line up along the equator (middle) of the cell

26. Cell Division in Eukaryotes
3. Anaphase:
Chromosomes are pulled apart at the centromere by spindles and separated into sister chromatids

27. Cell Division in Eukaryotes
4. Telophase
Sister chromatids reach opposite poles (sides of the cell)
Spindles disappear
Nuclear envelopes/membranes reappears
Cell begins to split into 2 new cells

28. Cell Division in Eukaryotes
3. Cytokinesis: dividing of the cell’s cytoplasm, forming two new cells
Animal cells: 2 new cells are separated by the cytoplasm “pinching in”

29. Cell Division in Eukaryotes
3. Cytokinesis:
Plant cells: 2 new cells cell plate separated by a cell plate that helps form the cell walls

30. Cell Division in Eukaryotes
3. Cytokinesis:

31. Cell Division in Eukaryotes
Meiosis: Cell division that produces gametes with half the number of chromosomes as the parent cell (haploid)
2 separate cell divisions: meiosis I and meiosis II
Interphase and Cytokinesis occur with both divisions

32. Cell Division in Eukaryotes
Meiosis starts with 1 diploid cell and ends with 4 haploid cells
Each gamete has half the number of chromosomes as a diploid cell
1 diploid cell with 4 chromosomes
4 haploid cells with 2 chromosomes each

33. Cell Division in Eukaryotes
MEIOSIS 1
Prophase I
DNA coils into tetrads (pair of homologous chromosomes)
Spindles appear
Nuclear envelope/membrane disappears
Crossing over occurs: DNA is swapped between chromosomes in a pair

34. Cell Division in Eukaryotes
MEIOSIS 1
Metaphase I
Tetrads are moved by the spindles and line up along the equator

35. Cell Division in Eukaryotes
MEIOSIS 1
Anaphase I
Tetrads pulled apart by the spindles and separated into chromosome
Chromosomes begin moving to opposite ends of the cell

36. Cell Division in Eukaryotes
MEIOSIS 1
Telophase I
Chromosomes reach opposite sides of the cell
Spindle disappears
Nuclear envelope/membrane reappears
Cytokinesis occurs after this step, forming 2 new cells, which then go through interphase again

37. Cell Division in Eukaryotes
Meiosis II--has 4 stages, PMAT II
Each stage--occurs just like the stages of mitosis
Prophase II
Metaphase II
Anaphase II
Telophase II

38. Cell Division in Eukaryotes
MEIOSIS II
Prophase II
Spindle appear in each of the 2 new cells
Nuclear envelopes/membranes disappears

39. Cell Division in Eukaryotes
MEIOSIS II
Metaphase II
Sister chromatids line up in the middle/equator of the cell.

40. Cell Division in Eukaryotes
MEIOSIS II
Anaphase II
Spindles split centromeres and sister chromatids separate
Chromatids start to move to opposite ends of the cell

41. Cell Division in Eukaryotes
MEIOSIS II
Telophase II
Sister chromatids (haploid) reach opposite ends of the cell
Spindles disappear
Nuclear envelopes/membranes appear
Cytokinesis follows this step forming 4 new cells

42. Cell Division in Eukaryotes
Sooooo, what happens after meiosis?
Sexual reproduction: production and combination of gametes
Fertilization: fusion of male and female gametes to form zygote
Zygote: diploid cell (2 of each chromosome)

43. Comparison of Types of Division
Mitosis
Meiosis
Occurs in most body cells
Occurs only in sex cells
One division
Two divisions
One cell makes 2 diploid cells
One cell makes 4 haploid cells
Identical to the parent
Different from parent