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02 cell division

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02 cell division

  1. 1. CELL DIVISION
  2. 2. CELL DIVISION Why do cells need to divide? -To allow an organism to grow. -To pass on genetic material. -To assist an organism's survival.
  3. 3. CELL DIVISION 2 types of cell division Mitosis Meiosis -daughter cells are genetically identical -daughter cells are genetically different
  4. 4. CELL DIVISION 2 types of cell division Mitosis Meiosis -daughter cells are genetically identical -daughter cells are genetically different -performed by somatic body cells (ex. bone nerve, or tissues) - performed to create sex cells (gametes: sperm and egg cells) - parts of the body with high rates of attrition must perform mitosis more often (ex. fingertips vs. liver cells)
  5. 5. CELL DIVISION 6 stages of cell division: 1) Interphase 2) Prophase 3) Metaphase 4) Anaphase 5) Telophase 6) Cytokinesis Mitosis - The division of the cell's nucleus and all genetic material.
  6. 6. CELL DIVISION Interphase - Cell is not dividing but also not dormant - Cell is active, growing, and preparing for division - Chromosomes are not visible (chromatin present).
  7. 7. CELL DIVISION Interphase: 4 stages Gap 0 (G0): - Cell rest cycle - Some cells spend their entire lives in G0 (they are functional but no new cells are produced (i.e. neuron) G0
  8. 8. CELL DIVISION Interphase: 4 stages Gap 1 (G1): - Rapid growth (4hrs) - Cell takes in nutrients for energy, growth, repair - Cells either go into S or G0 after G1 G0
  9. 9. CELL DIVISION Interphase: 4 stages S phase (S): - ~10 hrs - DNA synthesis/ replication - Cell duplicates its genetic material to make identical copies of its DNA. G0
  10. 10. CELL DIVISION Interphase: 4 stages Gap 2 phase (G2): - ~4 hrs - Second period of growth in preparation for cell division. -Cell grows larger in size. G0
  11. 11. CELL DIVISION S phase (S): Let’s take a closer look - The cell duplicates its DNA. - What is DNA? - Deoxyribonucleic acid. - Contains genetic information in coded form.
  12. 12. CELL DIVISION Deoxyribonucleic acid 2 Strands of attached nucleotides:
  13. 13. CELL DIVISION Deoxyribonucleic acid 2 Strands of nucleotides: - Phosphate (PO4) - Nucleobase - Sugar (deoxyribose)
  14. 14. CELL DIVISION Nucleotide bases enable the coding of genetic information. A – Adenine T – Thymine G – Guanine C – Cytosine Phosphates Sugars
  15. 15. CELL DIVISION - The "coded" information is the sequence of nucleotide bases A – Adenine T – Thymine G – Guanine C – Cytosine Every 3 nucleotide bases (called a codon) code for 1 specific amino acid.
  16. 16. CELL DIVISION DNA Codons - This is the genetic language. For example, A CG makes Threonine
  17. 17. CELL DIVISION On opposing strands: - A attracts only T - G attracts only C The bases attract through HYDROGEN BONDING. This is called complimentary base pairing.
  18. 18. CELL DIVISION - Adenine & Guanine are purines (2-ring nitrogenous bases). - Thymine & Cytosine are pyrimidines (1-ring nitrogenous bases). adenine
  19. 19. CELL DIVISION - C and G bond together with 3 hydrogen bonds. - A and T bond together with 2 hydrogen bonds.
  20. 20. CELL DIVISION - C and G bond together with 3 hydrogen bonds. - A and T bond together with 2 hydrogen bonds.
  21. 21. CELL DIVISION A&T C&G Which ones are A&T? Which ones are C&G? C&G A&T
  22. 22. CELL DIVISION - How does DNA replicate? STEP 1: Separation of the two DNA strands H-Bonds
  23. 23. CELL DIVISION - How does DNA replicate? STEP 2: Each parent strand attracts matching nucleotide bases to form a new chain (enzymes help). New chain Nucleotide bases
  24. 24. CELL DIVISION But DNA is a very long molecule. Does replication start from one end? Not usually. It can start at various points in "bubbles".
  25. 25. CELL DIVISION There are 3 models of replication:
  26. 26. CELL DIVISION …Back to interphase where DNA duplication occurs. DNA Replication Normally After duplication
  27. 27. CELL DIVISION But wait, how does all of the DNA remain organized in the nucleus? Why does it not tangle?
  28. 28. CELL DIVISION DNA strands are wrapped around histone proteins which act as “spools”.
  29. 29. CELL DIVISION Histone proteins that have been wrapped with DNA form “nucleosomes”.
  30. 30. CELL DIVISION Moving into mitosis… After interphase, the cell enters mitotic (M) phase: - Cell division occurs through: A) Mitosis – Process of dividing nuclear material. B) Cytokinesis - Process of separating the cytoplasm and its contents into equal parts. M phase takes ~2 hours in humans.
  31. 31. CELL DIVISION Prophase - Nuclear membrane and nucleolus break down. - Centrosome divides into 2 centrioles which begin forming the spindle fibres.
  32. 32. CELL DIVISION Prophase - Nuclear membrane and nucleolus break down. - Centrosome divides into 2 centrioles which begin forming the spindle fibres.
  33. 33. CELL DIVISION Prophase chromatin condenses
  34. 34. CELL DIVISION Prophase - Chromosomes shorten and thicken into Xshaped structures called dyads.
  35. 35. CELL DIVISION Prophase - Remember, every chromosome has been duplicated during the S phase of interphase. 2 copies of each chromosome: Father’s side Mother’s side Mitosis Father’s side Father’s side *Colors are not accurate Mother’s side Mother’s side
  36. 36. CELL DIVISION Prophase - A centromere holds two copies of the same chromosome together. - Each identical chromosome is called a sister chromatid.
  37. 37. CELL DIVISION Metaphase - Proteins attach to the centromeres creating the kinetochores. - Microtubules (spindle fibres) attach at the kinetochores and the chromosomes move to the centre (the metaphase plate)
  38. 38. CELL DIVISION Metaphase
  39. 39. CELL DIVISION Anaphase - Paired chromosomes separate at the kinetochores and move to opposite sides of the cell. - Motion results from kinetochore movement along the spindle microtubules.
  40. 40. CELL DIVISION Telophase - Chromatids arrive at opposite poles of cell. - New daughter nuclei form. - Chromosomes disperse and become chromatin. - Spindle fibres disperse.
  41. 41. CELL DIVISION Cytokinesis - Animal cells: the cell membrane pinches (forming a cleavage furrow) into two daughter cells, each with one nucleus
  42. 42. CELL DIVISION Cytokinesis - In plant cells, a cell plate (made of rigid cellulose) is synthesized between the two daughter cells.
  43. 43. CELL DIVISION Mitosis and cytokinesis: Review
  44. 44. CELL DIVISION Mitosis and cytokinesis: Haploid and Diploid Haploid = 1 set of chromosomes (ex. n=23 chromosomes) Diploid = 2 sets of chromosomes (ex. 2n= 46 chromosomes) Tetraploid = 4 sets of chromosomes (ex. 4n = 92 chromosomes) 2n 2n 2n 4n 4n
  45. 45. CELL DIVISION Karyotype: Photograph of chromosomes taken at the metaphase stage of mitosis. Homologous pairs are identified and placed together. daddy mommy Homologous pair
  46. 46. CELL DIVISION Karyotype: Technique 1) Treat the cells with a solution that will make them swell-up, which spreads the chromosomes. 2) Use a chemical to stop mitosis in metaphase. 3) Compress the cells on a slide and take a high resolution photograph. 5) Cutting up a photomicrograph and arranging the result into a karyogram.
  47. 47. CELL DIVISION Karyotype: Technique But during mitosis (metaphase), chromosomes are in duplicated pairs. So each homologous pair consists of 2 dyads. Scientists can cut the photographs so that only one chromatid of every dyad is displayed.
  48. 48. CELL DIVISION Homologous pairs Identified by: -chromosome length -centromere position -banding (staining) pattern -satellites (tips) and any other physical characteristics
  49. 49. CELL DIVISION Recall: 2 types of cell division Mitosis Meiosis -daughter cells are genetically identical -daughter cells are genetically different
  50. 50. CELL DIVISION Meiosis: The production of gametes -2 cell divisions (meiosis I and meiosis II) -Daughter cells are genetically unique -4 daughter cells are produced -Daughter cells are haploid
  51. 51. CELL DIVISION Meiosis I: Prophase I: -start with 2x the normal amount of chromosomes -chromosomes condense -nuclear membrane and nucleolus dissolve -centrioles split Same as mitosis
  52. 52. CELL DIVISION Meiosis I: Prophase I: -homologous dyads come together, forming tetrads -they overlap in a process called synapsis -crossing-over of genetic material, causing exchange of segments of DNA, producing recombinant chromosomes
  53. 53. CELL DIVISION Meiosis I: Prophase I: -dyads come together in homologous pairs, forming tetrads -they overlap in a process called synapsis -crossing-over occurs, causing exchange of segments of DNA tetrad
  54. 54. CELL DIVISION Meiosis I: Prophase I: Chiasma: crossover point
  55. 55. CELL DIVISION Meiosis I: Metaphase I -chromosomes attach themselves to spindle fibres -chromosomes line up at equatorial plate Same as mitosis, except the chromosomes are no longer identical (they are recombinant).
  56. 56. CELL DIVISION Meiosis I: Anaphase I - Homologous pairs separate and move to opposite poles of the cell (tetrads are pulled apart, dyads move to the poles) Same as mitosis, except the chromosomes are no longer identical (they are recombinant).
  57. 57. CELL DIVISION Meiosis I: Telophase I -cleavage furrow forms -nuclear membranes and nucleoli reform -chromosomes DO NOT un-condense Same as mitosis
  58. 58. CELL DIVISION Meiosis II: Second cell division (both Meiosis I daughter cells perform meiosis II) Phase Meiosis Prophase II -nuclear membranes and nucleoli dissolve -more spindle fibres form -chromosomes attach to spindle Metaphase II -chromosomes line up at equatorial plate Anaphase II -sister chromatids from each dyad separate and move to opposite poles Telophase II -spindle fibres dissipate -nuclei and nucleoli reform
  59. 59. CELL DIVISION
  60. 60. CELL DIVISION
  61. 61. CELL DIVISION
  62. 62. CELL DIVISION Mitosis 46 vs. Meiosis Diploid (2n) 46 Diploid (2n) Diploid (2n) 46 46 Diploid (2n) Diploid (2n) 46 46 Diploid (2n) 23 23 23 23 Haploid (1n) Haploid (1n) Haploid (1n) Haploid (1n)
  63. 63. CELL DIVISION Maternal Chromosome A Paternal Chromosome A 46 DNA Replication DNA Replication 92 92 Sister chromatids Division #1 (Meiosis I) Synapsis and crossing over Synapsis and crossing over 92 92 Metaphase I, anaphase I, & telophase I Metaphase I, anaphase I, & telophase I 46 46 46 46 Meiosis II Division #2 (Meiosis II) 23 23 23 23 23 23 23 23
  64. 64. CELL DIVISION Why is meiosis important? 1. allows continuity 2. ensures genetic diversity within population Diversity is generated through… 1) crossing-over (makes diverse chromosomes) 2) random assortment (each gamete is different) 3) random fertilization (random sperm meets with random mature egg)
  65. 65. CELL DIVISION How does this relate to Mendel? Before the process of meiosis was discovered, Mendel’s observations led him to make 2 conclusions: 1)Law of Segregation: 2 alleles for each trait separate during gamete formation (i.e. parents can only pass 1 of their 2 alleles for any trait to their offspring). Monohybrid cross
  66. 66. CELL DIVISION How does this relate to Mendel? 2)Law of Independent Assortment: Alleles from different chromosomes pass to gametes randomly – alleles are not connected to or passed on with any other alleles. For example, the allele for pea shape and the allele for pea color are passed onto offspring without relation to one-another. Dihybrid cross
  67. 67. CELL DIVISION How does this relate to Mendel? Made possible by the final division in Meiosis II Made possible by different chromosomes having different alleles All daughter cells are different
  68. 68. CELL DIVISION How does this relate to Mendel?
  69. 69. CELL DIVISION Mistakes during meiosis: Errors during Independent Assortment Non-disjunction Non-disjunction: Failure of dyads or tetrads to separate during anaphase I or anaphase II 46 44 22 22 Normal Meiosis 48 24 46 46 24 23 23 46 23 23
  70. 70. CELL DIVISION Mistakes during meiosis: Errors during Independent Assortment Aneuploidy: A condition that results when there is a missing or extra chromosome, resulting in changes to the normal chromosome number
  71. 71. CELL DIVISION Mistakes during meiosis: Errors during Independent Assortment What are the possible zygotes when a normal gamete is joined with a non-disjunct gamete? Non-disjunct egg egg 23 22 sperm 23 Non-disjunct sperm 24 45 47 Monosomy Trisomy
  72. 72. CELL DIVISION Mistakes during meiosis: Errors during Independent Assortment Monosomy: A condition in which an individual has only one homologue of a specific pair of homologues
  73. 73. CELL DIVISION Mistakes during meiosis: Errors during Independent Assortment Trisomy: A condition in which an individual has three homologues of a specific chromosome.
  74. 74. CELL DIVISION Mistakes during meiosis: Errors during Independent Assortment Polysomy: A condition in which an individual has more than the normal number of a specific chromosome.
  75. 75. CELL DIVISION Mistakes during meiosis: Errors during Independent Assortment Haploid (n): having one copy of an entire chromosome set (e.g. sex cells) Diploid (2n): having two copies of an entire chromosome set (e.g. somatic cells) Triploid (3n): having three copies of an entire chromosome set Polyploidy: A condition in which an individual has three or more copies of an entire chromosome set
  76. 76. CELL DIVISION Mistakes during meiosis: Errors during Independent Assortment How is it possible to get 3 or more copies of a chromosome?
  77. 77. CELL DIVISION Condition Final # of chromosomes Down 47 syndrome Affected chromosome Characteristic #21 Broad flat face, slanting eyes, short, growth failure, mental disabilities, congenital heart disease.
  78. 78. CELL DIVISION Condition Final # of chromosomes Turner’s 45 syndrome Affected chromosome Characteristic X Short, facial hair, undeveloped breast, degenerate ovaries, infertile. chromosome (sex chromosome)
  79. 79. CELL DIVISION Condition Final # of chromosomes Affected chromosome Klinefelter’s syndrome 47 or more X chromosome Characteristic Tall, longer limbs, poor beard growth, feminized physique, loose chest hairs, underdeveloped penis and testes, infertile
  80. 80. CELL DIVISION Condition Final # of chromosomes Affected chromosome Jacob’s syndrome 47 or more Y chromosome Characteristic Normal male, tall, “aggressive” (often unnoticed, 1/1000 males)
  81. 81. CELL DIVISION Condition Final # of chromosomes Affected chromosome Super female 47 or more X chromosome Characteristic Normal female, “aggressive”, taller, delayed motor skills, often unnoticed, 1/1000 females

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