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  • Mitosis

    2. 2. Outline <ul><li>Types of Cell Division </li></ul><ul><li>Structure of Chromosomes </li></ul><ul><li>Cell Division in Prokaryotes </li></ul><ul><li>Phases of cell cycle </li></ul><ul><li>Interphase </li></ul><ul><li>Mphase </li></ul><ul><li>Cytokinesis </li></ul><ul><li>Cell cycle-abnormalities </li></ul>
    3. 3. Cell Theory : all organisms consist of cells and arise from pre-existing cells <ul><li>Mitosis is the process by which new cells are generated for body tissues during development, growth, and tissue repair. </li></ul><ul><ul><li>2 cells are produced in one cycle of division </li></ul></ul><ul><ul><li>Daughter cells have ALL of the genetic material of the parent cell </li></ul></ul><ul><li>Meiosis is the process by which special cells called gametes are generated for reproduction. </li></ul><ul><ul><li>4 cells are produced in two cycles of division </li></ul></ul><ul><ul><li>Daughter cells have HALF the genetic material of the parent cell </li></ul></ul>
    5. 5. The state in which there are two copies of each chromosome present is known as diploid (2n).   H Haploid (n)– only one copy of a chromosome is present All of the somatic cells in our bodies are diploid cells The only cells in our bodies that are haploid are our gametes – eggs and sperm
    6. 6. Human somatic cells have 46 chromosomes diploid number (2n) = 46 23 from mom - 23 from dad 22 pairs are autosomes –true homologous pairs 1 pair is not necessarily homologous - sex chromosomes females are XX males are XY – a non homologous pair.
    7. 7. Meiosis – form of cell division where there are two successive rounds of cell division following DNA replication - produces haploid cells (n) - start with 46 double stranded chromosomes (2n) After 1 division - 23 double stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n)   - occurs in our germ cells – cells that produce our gametes - egg and sperm
    8. 8. Cell division Mitosis
    9. 9. Cell division All complex organisms originated from a single fertilized egg. Every cell in your body started here, through cell division the numbers are increased Cell then specialize and change into their various roles
    10. 10. Mitosis <ul><li>Mitosis is the process by which new body cell are produced for: </li></ul><ul><ul><li>Growth </li></ul></ul><ul><ul><li>Replacing damaged or old cells. </li></ul></ul><ul><ul><li>This is a complex process requiring different stages </li></ul></ul>
    11. 11. Mitosis <ul><li>All daughter cells contain the same genetic information from the original parent cell from which it was copied. </li></ul><ul><li>Every different type of cell in your body contains the same genes, but only some act to make the cells specialise – e.g. into nerve or muscle tissue. </li></ul>
    12. 12. BASIC GENETICS <ul><li>Each cell in the human body contains two sets of 2 3 chromosomes </li></ul><ul><li>Mitosis identically replicates this information </li></ul><ul><li>E ach cell therefore has the same </li></ul><ul><li>genetic material </li></ul><ul><li>Reproductive cells only have one set </li></ul><ul><li>of chromosomes. These combine to </li></ul><ul><li>make a new person with different </li></ul><ul><li>genetic material to both parents </li></ul>
    13. 13. 2 daughter cells identical to original Parent cell Chromosomes are copied and double in number Chromosomes now split
    14. 14. Reproduction presents a major problem for cells and organisms: (how can information be transmitted faithfully to progeny) I II III IV = one bit of genetic information
    15. 15. = one bit of genetic information The information transfer problem becomes more challenging as more bits of information are incorporated into the organism
    16. 16. One of life’s solutions to this challenge: “Package” the bits of information into single units called chromosomes = one bit of genetic information
    17. 17. The nucleus <ul><li>Nuclear membrane - double membrane </li></ul><ul><li>Chromosomes/Chromatin- genetic material/DNA </li></ul><ul><li>Gene - DNA segment </li></ul><ul><li>Chromosome---  DNA ---  Gene </li></ul>
    18. 18. chromosomes Packaging of genetic material in prokaryotes and eukaryotes prokaryote cell eukaryote cell
    19. 19. Structure of Chromosomes <ul><li>Chromosomes are composed of a complex of DNA and protein, chromatin. </li></ul><ul><li>DNA exists as a single, long, double-stranded fiber extending chromosome’s entire length. </li></ul><ul><ul><li>forms nucleosome every 200 nucleotides </li></ul></ul><ul><ul><ul><li>DNA coiled around histone proteins </li></ul></ul></ul>
    20. 20. C Chromosome basics . T The number of chromosomes present within the nucleus is a characteristic of the species. Chromosomes of humans and most other eukaryotic species occurs in pairs. Members of a chromosome pair are known as homologues.
    21. 21. Mitosis/Cell division mitosis is the process of cell division in which one cell becomes two identical daughter cells development renewal regeneration
    22. 22. The cell cycle is the mechanism by which a cell duplicates its contents and then divides in two cell grows and duplicates its contents cell contents cell divides in two Each parental cell gives rise to two daughter cells on completion of each cell cycle parental cell daughter cell 1 daughter cell 2
    23. 23. Replication of chromosomes <ul><li>Replication is the process of duplicating a chromosome </li></ul><ul><li>Occurs prior to division </li></ul><ul><li>Replicated copies are </li></ul><ul><li>called sister chromatids </li></ul><ul><li>Held together at centromere </li></ul>
    24. 25. Binary Fission-prokaryotic cells
    25. 26. Cell Cycle
    26. 27. Prophase Metaphase Anaphase Telophase The Stages of M itosis Interphase
    27. 28. REMEMBER! <ul><li>I nterphase </li></ul><ul><li>P rophase </li></ul><ul><li>M etaphase </li></ul><ul><li>A naphase </li></ul><ul><li>T elophase </li></ul>(Individuals Please Make All The Cells) IPMAT
    28. 29. INTERPHASE <ul><li>After a cell has divided, the two </li></ul><ul><li>new cells begin the process again, </li></ul><ul><li>the cell s at this stage are in </li></ul><ul><li>Interphase. </li></ul>
    29. 30. <ul><li>By late interphase, the chromosomes have been duplicated but are loosely packed. </li></ul><ul><li>The centrosomes have been duplicated and begin to organize microtubules into an aster (“star”). </li></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
    30. 32. PROPHASE <ul><li>The chromatin (decondensed DNA) in the nucleus, condenses to form pairs of chromosomes . </li></ul><ul><li>The centrioles move to opposite </li></ul><ul><li>ends of the nucleus. </li></ul><ul><li>As this is happening the nucleolus </li></ul><ul><li>begins to break down </li></ul><ul><li>Nuclear membrane begins to break down </li></ul>
    31. 33. Prophase <ul><li>Replicated chromosomes condense. </li></ul><ul><li>Microtubules organize into a spindle </li></ul>
    32. 34. The Spindle <ul><li>A spindle is a web type structure made up of microtubule fibers. It is essential for mitosis because it arranges the chromosomes into their correct positions in preparation for cell division. </li></ul>Mitotic center Microtubule A cell at metaphase a spindle
    33. 35. Chromosomes attached to spindle during nuclear division
    34. 36. METAPHASE <ul><li>The spindle becomes fully developed </li></ul><ul><li>The nuclear membrane has completely gone </li></ul><ul><li>The chromatid pairs </li></ul><ul><li>are aligned along </li></ul><ul><li>the center of the </li></ul><ul><li>spindle (the EQUATOR) </li></ul>
    35. 37. <ul><li>The spindle fibers push the sister chromatids until they are all arranged at the metaphase plate , an imaginary plane equidistant between the poles, defining metaphase. </li></ul>Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
    36. 38. Anaphase <ul><li>Centromeres of sister chromatids separate </li></ul><ul><li>Chromosomes move to opposite ends of the cell </li></ul>
    37. 39. <ul><li>At anaphase, the centromeres divide, separating the sister chromatids. </li></ul><ul><li>Each is now pulled toward the pole to which it is attached by spindle fibers. </li></ul><ul><li>By the end, the two poles have equivalent collections of chromosomes. </li></ul>
    38. 40. TELOPHASE Two new nuclei are formed when the chromosomes reach the opposite poles of the cell The nuclear membrane is formed- the nucleolus reappears The chromosomes disperse in the nucleus
    39. 41. Telophase <ul><li>Nuclear membranes form </li></ul><ul><li>Spindle disappears </li></ul><ul><li>Division of cytoplasm occurs (cytokinesis) </li></ul>
    40. 42. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
    41. 43. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
    42. 44. CYTOKINESIS <ul><li>Literally means, division of the cytoplasm </li></ul><ul><li>M itosis is the splitting of the nucleus. </li></ul><ul><li>Cytokinesis is the splitting of cytoplasm </li></ul>
    43. 45. Cytokinesis <ul><li>Cleavage of cell into two halves </li></ul><ul><ul><li>animal cells </li></ul></ul><ul><ul><ul><li>constriction belt of actin filaments </li></ul></ul></ul><ul><ul><li>plant cells </li></ul></ul><ul><ul><ul><li>cell plate </li></ul></ul></ul>
    44. 46. Cytokinesis <ul><li>Cytoplasmic division </li></ul><ul><li>occurs after nuclear </li></ul><ul><li>division is complete. </li></ul><ul><li>Two cells are formed. </li></ul>
    45. 47. Cytokinesis in animals A cleavage furrow forms that pinches the cell in two - the furrow represents a ring of actin and myosin filaments just under the plasma membrane.
    46. 48. Rat – epithelial cells
    47. 49. Mitosis – bone cell slides 1 2 3 4 5 Parent cell Chromosomes copied Copies separating 2 daughter cells Cells split
    48. 50. Cytokinesis in plants A cell plate made up of cell-wall components gradually forms in the middle of the cell.
    49. 51. So what’s the difference in Plants? <ul><li>Plant cells do not have a centriole </li></ul><ul><li>Plant cells do not pinch in half. </li></ul><ul><li>Cytoplasmic division is accomplished by a cell plate forming between 2 daughter cells </li></ul>
    50. 52. Plants
    51. 53. Cell Turnover – The speed of mitosis <ul><li>One full cycle can vary between a couple of minutes to days. </li></ul><ul><li>For example s kin and epithelial cells have a rapid turnover in the human body in order to replace the ones constantly being worn away. </li></ul><ul><li>C ells which make up organs such as the eye and the brain, need not multiply as often once they reach adult size. </li></ul>
    52. 54. <ul><li>Organs which need to produce new cells continuously have the highest turnover . </li></ul><ul><li>For example :- </li></ul><ul><ul><li>Bone marrow- </li></ul></ul><ul><ul><li>producing replacement </li></ul></ul><ul><ul><li>blood cells </li></ul></ul><ul><ul><li>The testes - producing </li></ul></ul><ul><ul><li>spermatogonia </li></ul></ul>
    53. 55. Tumors <ul><li>Abnormalities can sometimes occur in c ells which reproduce at a rapid rate, this in turn may lead to the formation of tumors. </li></ul><ul><li>Tumors of any type should be considered serious. </li></ul><ul><li>Although benign tumors do n o t usually cause a threat to a persons life , they can cause great inconvenience if not treated. </li></ul>
    54. 56. CANCER <ul><li>uncontrolled cellular mitotic divisions </li></ul>
    55. 57. Meiosis
    56. 58. Meiosis – A Source of Distinction Why do you share some but not all characters of each parent? What are the rules of this sharing game? At one level, the answers lie in meiosis.
    57. 59. Meiosis does two things - 1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). This is a good idea if you’re going to combine two cells to make a new organism. This trick is accomplished by halving chromosome number. In meiosis, one diploid cells produces four haploid cells.
    58. 60. Why do we need meiosis? <ul><li>Meiosis is necessary to halve the number of chromosomes going into the sex cells </li></ul><ul><li>Why halve the chromosomes in gametes? </li></ul><ul><li>At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents </li></ul>
    59. 61. 2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives. This makes for a lot of genetic diversity . This trick is accomplished through independent assortment and crossing-over . Genetic diversity is important for the evolution of populations and species .
    60. 62. Meiosis Parent cell – chromosome pair Chromosomes copied 1 st division - pairs split 2 nd division – produces 4 gamete cells with ½ the original no. of chromosomes
    61. 63. Meiosis – mouse testes Parent cell 4 gametes 1 st division 2 nd division
    62. 64. The Stages of Meiosis: <ul><li>aka: Reduction Division </li></ul>
    63. 65. Meiosis I : Separates Homologous Chromosomes <ul><li>Interphase </li></ul><ul><ul><li>Each of the chromosomes replicate </li></ul></ul><ul><ul><li>The result is two genetically identical sister chromatids which remain attached at their centromeres </li></ul></ul>
    64. 66. Prophase I <ul><li>During this phase each pair of chromatids match up with their homologous pair and fasten together (synapsis) in a group of four called a tetrad. </li></ul><ul><li>Extremely IMPORTANT!!! It is during this phase that crossing over can occur. </li></ul><ul><li>Crossing Over is the exchange of segments during synapsis. </li></ul>
    65. 67. Metaphase I <ul><li>The chromosomes line up at the equator attached by their centromeres to spindle fibers from centrioles. </li></ul><ul><ul><li>Still in homologous pairs </li></ul></ul>
    66. 68. Anaphase I <ul><li>The spindle guides the movement of the chromosomes toward the poles </li></ul><ul><ul><li>Sister chromatids remain attached </li></ul></ul><ul><ul><li>Move as a unit towards the same pole </li></ul></ul><ul><li>The homologous chromosome moves toward the opposite pole </li></ul><ul><ul><li>Contrasts mitosis – chromosomes appear as individuals instead of pairs (meiosis) </li></ul></ul>
    67. 69. Telophase I <ul><li>This is the end of the first meiotic cell division. </li></ul><ul><li>The cytoplasm divides, forming two new daughter cells. </li></ul><ul><li>Each of the newly formed cells has half the number of the parent cell’s chromosomes, but each chromosome is ready for the second meiotic cell division </li></ul>
    68. 70. Cytokinesis <ul><li>Occurs simultaneously with telophase I </li></ul><ul><ul><li>Forms 2 daughter cells </li></ul></ul><ul><li>Plant cells – cell plate </li></ul><ul><li>Animal cells – cleavage furrows </li></ul><ul><li>NO FURTHER REPLICATION OF GENETIC MATERIAL PRIOR TO THE SECOND DIVISION OF MEIOSIS </li></ul>
    69. 71. Figure 13.7 The stages of meiotic cell division: Meiosis I
    70. 72. Meiosis II : Separates sister chromatids <ul><li>Similar to mitosis </li></ul><ul><li>THERE IS NO INTERPHASE II ! </li></ul>
    71. 73. Prophase II <ul><li>Each of the daughter cells forms a spindle, and the double stranded chromosomes move toward the equator </li></ul>
    72. 74. Metaphase II <ul><li>The chromosomes are positioned on the metaphase plate in a mitosis-like fashion </li></ul>
    73. 75. Anaphase II <ul><li>The centromeres of sister chromatids finally separate </li></ul><ul><li>The sister chromatids of each pair move toward opposite poles </li></ul><ul><ul><li>Now individual chromosomes </li></ul></ul>
    74. 76. Telophase II and Cytokinesis <ul><li>Nuclei form at opposite poles of the cell and cytokinesis occurs </li></ul><ul><li>After completion of cytokinesis there are four daughter cells </li></ul><ul><ul><li>All are haploid (n) </li></ul></ul>
    75. 77. Figure 13.7 The stages of meiotic cell division: Meiosis II
    76. 78. One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2 n distinct gametes, where n = the number of unique chromosomes. That’s a lot of diversity by this mechanism alone. In humans, n = 23 and 2 23 = 6,000,0000.
    77. 80. Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.
    78. 81. Mitosis vs. Meiosis
    79. 82. The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The first (and distinguishing) division of meiosis
    80. 83. Mitosis vs. Meiosis
    81. 84. Boy or Girl? The Y Chromosome “Decides” X chromosome Y chromosome
    82. 85. Boy or Girl? The Y Chromosome “Decides”
    83. 86. Meiosis – division error Chromosome pair
    84. 87. Meiosis error - fertilization Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’. In humans this often occurs with the 21 st pair – producing a child with Downs Syndrome
    85. 88. 21 trisomy – Downs Syndrome Can you see the extra 21 st chromosome? Is this person male or female?