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Cell Growth and Division:

Cell Growth and Division:. Mitosis vs. Meiosis and What’s going on the rest of the time. 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. The same happens with a cell. What is the surface area?

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Cell Growth and Division:

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  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

  13. 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.

  14. 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

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

  16. 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

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

  18. 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

  19. 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

  20. 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

  21. 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

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

  23. 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

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

  25. Centromere Telomeres

  26. 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

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

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

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

  30. 1. Prophase • Nuclear membrane breaks down • Nucleolus disappears

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

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

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

  34. 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

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

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

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

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

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

  40. 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

  41. 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!!!

  42. 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

  43. 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

  44. 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

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

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

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

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

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

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