Unlocking Cell Growth & Division: Mitosis vs. Meiosis

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

19. A B C D E A B C D E 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

20. 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. 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. Chromosome Analogy • Homologous Chromosomes = Volume “A” from each encycl. A A HomologousChromosomes

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

25. 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