Chapter 10: Cell Division and Growth

1. Chapter 10: Cell Division and Growth

2. Chromosomes • When cells are NOT dividing, DNA is found in the nucleus in the form of uncoiledchromatin. • 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 chromosomes Centromere 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. A a B b The letters are the genes Upper case and lower case letters are versions of the genes C c D d E e F f

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 movingto 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/equatorof 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) http://video.sciencemag.org/VideoLab/2127025888001/1/medicine

43. Comparison of Types of Division