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Mitosis and cytokinesis


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Mitosis and cytokinesis

  1. 1. Cell Division and Genetics – Mechanisms for a Knit of Identity and Thread of Distinction
  2. 2. DNA and Its Faithful Replication – The Knit of Identity Because DNA stores genetic information and is faithfully replicated, information is passed largely unaltered from cell-to-cell, generation-to- generation.
  3. 3. Proteins and Their Production – The Primary Reason for DNA
  4. 4. Cell Division Demands Coordination of DNA Replication, Mitosis and Cytokinesis What’s so important about cell division?
  5. 5. Cell division requires coordinated division of chromosomes (mitosis) ….. …… and division of the cytoplasm (cytokinesis).
  6. 6. DNA Replication – Simple in Principle, Complicated in Practice
  7. 7. DNA is Packaged into Chromosomes DNA in the cell is virtually always associated with proteins. The packaging is impressive – 2 meters of human DNA fit into a sphere about 0.000005 meters in diameter. chromatin duplicated chromosome
  8. 8. The Link Between DNA Replication and Chromosome Duplication
  9. 9. DNA is Condensed into Visible Chromosomes Only For Brief Periods in the Life of a Cell 95% of the time, chromosomes are like this. Easily visible chromosomes are apparent perhaps 5% of the time in an actively growing cell and less in a non-growing cell.
  10. 10. A Karyotype is an Arranged Picture of Chromosomes At Their Most Condensed State A normal human karyotype Boy or girl? Note that almost all chromosomes come in homologous pairs.
  11. 11. From Birth to Rebirth, a Cell Progresses Through Characteristic Stages That Constitute the Cell Cycle In multicellular organisms like us, progress through the cell cycle is carefully regulated.
  12. 12. Cancer Is One Outcome of A Runaway Cell Cycle Licentious division - prostate cancer cells during division.
  13. 13. The Knit of Identity - Mitosis Precisely and Evenly Divides Duplicated Chromosomes Precisely dividing the duplicated chromosomes has the consequence of providing each new cell with an identical and complete set of genetic instructions. interphase prophase metaphase
  14. 14. Mitosis Precisely and Evenly Divides Duplicated Chromosomes Cytokinesis is the process of cell division and it is distinct and separable from mitosis.
  15. 15. Mitosis in Action Blue shows DNA, green shows spindle fibers.
  16. 16. In Animal Cells, a Cleavage Furrow Forms and Separates Daughter Cells Cleave furrow in a dividing frog cell.
  17. 17. The Plant Cell Wall Forces Cytokinesis to Play by Different Rules
  18. 18. Part 1: Cell Division <ul><li>Cell division is the cornerstone of life </li></ul><ul><li>Genome : an organisms complete set of genetic material (DNA) </li></ul>
  19. 19. Prokaryotic Chromosomes <ul><ul><li>Bacteria & viruses </li></ul></ul><ul><ul><li>A single DNA (or RNA in some virusis) moleucle that contains all the genetic information for the individual. </li></ul></ul>
  20. 20. Chromosomes ( colored bodies ) <ul><li>Prokaryotes have a single, circular chromosome </li></ul>
  21. 21. <ul><ul><li>Prokaryotes (bacteria) reproduce through cell division called Binary fission </li></ul></ul><ul><ul><li>Circular chromosome (DNA) is replicated </li></ul></ul><ul><ul><li>Replicated chromosomes are attached to the cell membrane at nearby sites </li></ul></ul><ul><ul><li>As membrane expands, the copies separate </li></ul></ul><ul><ul><li>New cell wall forms between copies, cell splits </li></ul></ul>
  22. 22. Eukaryotic Chromosomes <ul><ul><li>DNA & protein structures with only part of the DNA information. All of the chromosome together make up the genome. </li></ul></ul>
  23. 23. Mitosis <ul><ul><li>Eukaryotes use cell division to create new cells </li></ul></ul><ul><ul><li>MITOSIS : division of the nucleus. Responsible for Growth, Maintenance and Repair </li></ul></ul><ul><li>Type of Asexual cell division </li></ul>
  24. 24. Chromosomes (colored bodies) <ul><li>Chromosome made of a DNA and protein complex: chromatin. Following DNA replication, a chromosome contains two sister chromatids attached by a centromere </li></ul>
  25. 25. Human Chromosomes: 46 <ul><ul><li>46 chromosomes (2n = 46) </li></ul></ul><ul><ul><ul><li>2 sets of 23 chromosomes ( diploid ) </li></ul></ul></ul><ul><ul><ul><ul><li>n = number of chromosomes in a set </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Fundamental number, haploid number </li></ul></ul></ul></ul><ul><ul><li>n = contribution from each parent </li></ul></ul><ul><ul><li>23 = 1 sex chromosome , 22 autosomes </li></ul></ul>
  26. 26. Mitosis and Interphase Alternate <ul><li>The cell cycle </li></ul><ul><ul><li>Cells are in interphase from 75-90% of the time </li></ul></ul><ul><ul><li>G1 = Gap 1 (cell growth) </li></ul></ul><ul><ul><li>S = chromosome synthesis (duplication) </li></ul></ul><ul><ul><li>G2 = Gap 2 (cell growth) </li></ul></ul><ul><ul><li>M = Mitosis </li></ul></ul>
  27. 27. Chromosomes cont. Homologous pair (2n, diploid) in parent cell <ul><li>Chromosomes are replicated during S-phase of cell cycle. Chromosomes and copies are separated during mitosis. </li></ul>One of each pair to daughter cell Copies
  28. 28. Mitosis is a Continuum
  29. 29. Prophase <ul><ul><li>Chromatin coils into visible chromosomes </li></ul></ul>Under a light microscope, only the nuclear envelope (with nucleoli) and a tangle of chromatin are visible
  30. 30. Pro-metaphase (late prophase) <ul><li>Nuclear envelope breaks </li></ul><ul><li>Microtubules attach centromere to centrioles </li></ul>
  31. 31. Metaphase <ul><li>Chromatids align on a plane at cell’s equator </li></ul>
  32. 32. Anaphase <ul><li>Chromatids separate simultanously </li></ul><ul><li>Sister chromatids become daughter chromosomes </li></ul>
  33. 33. Telophase <ul><ul><li>Daughter chromosomes stop moving </li></ul></ul><ul><ul><li>Chromosomes uncoil, nucleus and nucleoli reform resulting in two new, identical cells. </li></ul></ul>
  34. 34. Cytokinesis <ul><li>Division of cell cytoplasm after mitosis is known as cytokinesis </li></ul>
  35. 35. Phases of the Cell Cycle <ul><li>The cell cycle consists of </li></ul><ul><ul><li>Interphase </li></ul></ul><ul><ul><li>Mitosis </li></ul></ul><ul><ul><li>Cytokinesis </li></ul></ul>INTERPHASE G 1 S (DNA synthesis) G 2 Cytokinesis Mitosis MITOTIC (M) PHASE Figure 12.5
  36. 36. <ul><li>Heredity </li></ul><ul><ul><li>Is the transmission of traits from one generation to the next </li></ul></ul><ul><li>Variation </li></ul><ul><ul><li>Shows that offspring differ somewhat in appearance from parents and siblings </li></ul></ul>Figure 13.1
  37. 37. <ul><li>Genetics </li></ul><ul><ul><li>Is the scientific study of heredity and hereditary variation </li></ul></ul><ul><ul><li>Offspring acquire genes from parents by inheriting chromosomes </li></ul></ul>
  38. 38. Inheritance of Genes <ul><li>Genes </li></ul><ul><ul><li>Are the units of heredity </li></ul></ul><ul><ul><li>Are segments of DNA </li></ul></ul>
  39. 39. <ul><li>Each gene in an organism’s DNA </li></ul><ul><ul><li>Has a specific locus (location) on a certain chromosome </li></ul></ul><ul><li>We inherit </li></ul><ul><ul><li>One set of chromosomes from our mother and one set from our father </li></ul></ul>
  40. 40. Comparison of Asexual and Sexual Reproduction <ul><li>In asexual reproduction (mitosis) </li></ul><ul><ul><li>One parent produces genetically identical offspring by mitosis </li></ul></ul>Figure 13.2 Parent Bud 0.5 mm
  41. 41. <ul><li>In sexual reproduction </li></ul><ul><ul><li>Two parents give rise to offspring that have unique combinations of genes inherited from the two parents </li></ul></ul>
  42. 42. <ul><li>Genes are located on Chromosomes </li></ul><ul><li>Individuals inherit two sets of genes (chromosome) – one from each parent </li></ul><ul><li>These “Matching” chromosomes are called Homologous chromosomes, because they carry genes for the “same” (homo) traits </li></ul><ul><ul><li>Have genes for the same characteristics </li></ul></ul><ul><ul><li>Are also be called autosomes </li></ul></ul>
  43. 43. <ul><li>Sex chromosomes </li></ul><ul><ul><li>Are distinct from each other and carry genes for different triats </li></ul></ul><ul><ul><li>We all inherit two sex chromosomes, one from each parent </li></ul></ul><ul><ul><li>represented as X and Y </li></ul></ul><ul><ul><li>Determine the sex of the individual </li></ul></ul><ul><ul><ul><li>XX = female, </li></ul></ul></ul><ul><ul><ul><li>XY = male </li></ul></ul></ul>
  44. 44. <ul><li>A diploid cell (2n) </li></ul><ul><ul><li>Has two sets of each of its chromosomes </li></ul></ul><ul><ul><li>Human have 46 chromosomes (2 n = 46) </li></ul></ul>
  45. 45. <ul><li>We have a “Problem” in sexual reproduction </li></ul><ul><ul><li>How can we have 46 chromosomes in our cells, combine a cell from a father and a mother, and still have only 46 chromosomes in the offspring’s cells? </li></ul></ul><ul><ul><li>46 (father) + 46 (mother) = 46 (offspring) </li></ul></ul><ul><ul><li>There must be a way to reduce the number of chromosomes in the parents to half the number (23 for humans) </li></ul></ul>
  46. 46. Behavior of Chromosome Sets in the Human Life Cycle <ul><li>At sexual maturity </li></ul><ul><ul><li>The ovaries and testes produce special haploid (n) cells by meiosis </li></ul></ul><ul><ul><li>The cells are called gametes </li></ul></ul><ul><ul><li>Gametes , sperm and egg cells are haploid cells, containing only one set of chromosomes </li></ul></ul><ul><ul><li>In humans, the haploid (n) number is = 23, ½ of our diploid number (2n) </li></ul></ul>
  47. 47. <ul><li>Meiosis reduces the number of chromosome sets from diploid to haploid </li></ul><ul><li>Meiosis </li></ul><ul><ul><li>Takes place in two sets of divisions, meiosis I and meiosis II </li></ul></ul>
  48. 48. <ul><li>Meiosis I </li></ul><ul><ul><li>Reduces the number of chromosomes from diploid to haploid </li></ul></ul><ul><li>Meiosis II </li></ul><ul><ul><li>Produces four haploid daughter cells </li></ul></ul>
  49. 49. <ul><li>An Overview of Meiosis </li></ul><ul><li>Meiosis I </li></ul><ul><ul><li>Reduces the number of chromosomes from diploid to haploid </li></ul></ul><ul><li>Meiosis II </li></ul><ul><ul><li>Produces four haploid daughter cells </li></ul></ul>Figure 13.7 Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes 1 2 Homologous chromosomes separate Haploid cells with replicated chromosomes Sister chromatids separate Haploid cells with unreplicated chromosomes Meiosis I Meiosis II
  50. 50. <ul><li>The haploid reproductive cells are the gametes </li></ul><ul><li>Meiosis only occurs in the sex organs </li></ul><ul><ul><li>Males  testes to produce sperm </li></ul></ul><ul><ul><li>Females  ovaries to produce eggs </li></ul></ul><ul><li>Gametes are not produced until the individual reaches puberty and special hormones “kick” in and start the process </li></ul><ul><ul><li>Males  testosterone </li></ul></ul><ul><ul><li>Females  estrogen & progesterone </li></ul></ul>
  51. 51. Newborn (2n) Growth Development Maintenance Repair Gametogenesis Adult (2n) Growth Development Maintenance Repair Mitosis Gametes Egg (n) Sperm (n) Meiosis Zygote (2n) Embryo (2n) Mitosis Growth Development Maintenance Repair Mitosis Growth Mitosis
  52. 52. <ul><li>Reshuffling of genetic material in meiosis </li></ul><ul><ul><li>Produces genetic variation </li></ul></ul>
  53. 53. Origins of Genetic Variation Among Offspring <ul><li>In species that produce sexually </li></ul><ul><ul><li>The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises each generation </li></ul></ul>
  54. 54. Independent Assortment of Chromosomes <ul><li>Homologous pairs of chromosomes </li></ul><ul><ul><li>Orient randomly at metaphase I of meiosis </li></ul></ul>
  55. 55. <ul><li>In independent assortment </li></ul><ul><ul><li>Each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs </li></ul></ul>Figure 13.10 Key Maternal set of chromosomes Paternal set of chromosomes Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Possibility 2 Metaphase II Daughter cells Combination 1 Combination 2 Combination 3 Combination 4
  56. 56. <ul><li>Interphase and meiosis I </li></ul>Figure 13.8 Centrosomes (with centriole pairs) Sister chromatids Chiasmata Spindle Tetrad Nuclear envelope Chromatin Centromere (with kinetochore) Microtubule attached to kinetochore Tetrads line up Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Pairs of homologous chromosomes split up Chromosomes duplicate Homologous chromosomes (red and blue) pair and exchange segments; 2 n = 6 in this example INTERPHASE MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I
  57. 57. <ul><li>Telophase I, cytokinesis, and meiosis II </li></ul>TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS MEIOSIS II: Separates sister chromatids Cleavage furrow Sister chromatids separate During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes Two haploid cells form; chromosomes are still double Haploid daughter cells forming Figure 13.8
  58. 58. <ul><li>A comparison of mitosis and meiosis </li></ul>Figure 13.9 MITOSIS MEIOSIS Prophase Duplicated chromosome (two sister chromatids) Chromosome replication Chromosome replication Parent cell (before chromosome replication) Chiasma (site of crossing over) Prophase I Tetrad formed by synapsis of homologous chromosomes Metaphase Chromosomes positioned at themetaphase plate Tetrads positioned at the metaphase plate Metaphase I Anaphase I Telophase I Haploid n = 3 MEIOSIS II Daughter cells of meiosis I Homologues separate during anaphase I; sister chromatids remain together Daughter cells of meiosis II n n n n Sister chromatids separate during anaphase II Anaphase Telophase Sister chromatids separate during anaphase 2 n 2 n Daughter cells of mitosis 2 n = 6 MEIOSIS I
  59. 59. A Comparison of Mitosis and Meiosis <ul><li>Meiosis and mitosis can be distinguished from mitosis by three events in Meiosis l </li></ul><ul><ul><li>Crossing over: homologous chromosomes physically connect and exchange genetic information </li></ul></ul><ul><ul><li>paired homologous chromosomes (tetrads) are positioned in the middle of the cell </li></ul></ul><ul><ul><li>At anaphase I of meiosis , homologous pairs move toward opposite poles of the cell </li></ul></ul><ul><ul><li>In anaphase II of meiosis , the sister chromatids separate </li></ul></ul>