Cell Reproduction
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  • 1. Cell Reproduction Mitosis & Meiosis
  • 2. Why Cells Divide
    • Surface Area/ Volume Ratio
      • As the cell grows, the volume increases at a greater rate than the surface area
      • Can't take in enough nutrients, or remove wastes
      • Therefore the cell must grow or divide
    • Growth and Repair
      • Replace worn or damaged cells
      • Frequency of replacement varies:
        • bacteria ~ every 20 minutes
        • human cells ~ every 18-22 hours
      • Many cells in the body don't divide
  • 3. Cell Division
  • 4. Cellular Reproduction
    • When the parent cell divides, it forms new daughter cells
    • Organisms reproduce in two ways:
      • Asexual Reproduction
      • Sexual Reproduction
  • 5. Sexual vs. Asexual Reproduction
    • Asexual Reproduction
      • production of offspring from one parent
      • therefore genetic material is identical to parent
    • Sexual Reproduction
      • formation of a new individual from the union of 2 cells
      • 2 parents, therefore offspring have some hereditary material from each
  • 6. Types of Asexual Reproduction
    • Binary Fission
      • simplest form; the cell splits in 2
    • Spore Formation
      • Begins with replication
      • Spores can remain inactive until conditions are favorable
      • molds, fungi
    • Yeast reproduce by budding
    • Vegetative Propagation
      • Some plants, e.g. strawberries
    • Regeneration
      • planaria, star fish, etc.
  • 7. Cell Division in Prokaryotes
    • Binary Fission:
    • The simplest form of cell division
    • The cell splits in 2
  • 8. The Process of Binary Fission
    • First the single circular chromosome duplicates = Replication
    • Both chromosomes attach to sites on the cell membrane
    • As the cell grows, a new membrane forms between attachment sites
    • Membrane pinches off and the new cells separate
  • 9. Sexual Reproduction
    • The joining of 2 specialized sex cells called gametes
      • male = sperm
      • female = ovum
    • Process of combining gametes = fertilization
    • Fertilization produces a zygote
      • has characteristics of both parents
  • 10. Human Sexual Reproduction
    • Male testis produces sperm
    • Female ovary produces ova
    • Each has 23 chromosomes
    • Unite to form a zygote with 46 chromosomes
      • 23 pair
    • Develops into a fetus
  • 11. Cell Division
    • All types of reproduction require cell division
    • 2 processes can be used to divide the cell’s nuclear material:
    • Mitosis
      • Occurs in somatic cells (body cells) in eukaryotes
      • As a result of mitosis each daughter cell receives an exact copy of the chromosomes present in the parent cell
    • Meiosis
      • Occurs in gametes (sex cells)
      • As a result each daughter cell receives 1 of each pair of chromosomes present in the parent cell
  • 12. Mitosis
    • Cell division in eukaryotic cells involves nuclear division called mitosis
    • Occurs in somatic cells
      • body cells; not sex cells
    • As a result of mitosis, each daughter cell receives an exact copy of the chromosomes present in the parent cell
    • Chromosomes contain genetic material
      • DNA
  • 13. Chromosomes
    • During cell division in eukaryotic cells, the DNA is coiled into chromosomes
    • Every body cell of the same type of organism has the same number of chromosomes
      • humans = 46
      • goldfish = 94
      • mosquito = 6
  • 14. Chromosome Structure
    • Each chromosome is formed from two joined strands called chromatids
    • Each chromatid is alike
      • has a long arm & a short arm
      • joined at the centromere
    • Chromosomes contain DNA and associated proreins
  • 15. Chromosomal Proteins
    • Each chromosome is a single DNA molecule and associated proteins
    • Histones –
      • One type of chromosomal protein
      • The DNA wraps tightly around the histones
      • Histones help maintain the shape of the chromosome
    • Nonhistone proteins -
      • control the activity of specific regions of DNA
  • 16. Picturing Chromosome Structure
  • 17. Visualizing Chromosomes
  • 18. Chromosome Make-up
    • Chromosomes of somatic cells are in pairs
      • One of each pair comes from mother, one from father
    • The 2 chromosomes in a pair are homologous
      • Alike in appearance and type of genetic information carried
    • Humans have 23 pairs of chromosomes
      • 22 pairs of autosomes
        • Autosomes are all but the sex
      • 2 sex chromosomes ( X & Y)
  • 19. Sex Chromosomes
    • Determine the sex of the organism
    • Also carry other genetic information
    • In humans, either X or Y
    • Females are XX, males are XY
    • Thus the male determines the sex of the offspring
  • 20. Haploid vs. Diploid
    • Cells with two copies of each chromosome = diploid
    • Autosomal cells are diploid
    • Gametes (sex cells) have only one of each type of chromosome
    • Cells with one copy of each chromosome = haploid
  • 21. Karyotypes
    • A picture of paired human chromosomes
    • Used to to detect certain genetic diseases
  • 22.  
  • 23. Mitosis
    • The process of dividing the nuclear material in a somatic cell in eukaryotes
    • Necessary for cell division
  • 24. Preparation for Mitosis
    • Interphase
      • The time between the formation of a cell through mitosis and the next mitosis
    • Most of the cell cycle is interphase
    • During this phase cell prepares by:
      • replicating genetic material
      • producing organelles
      • assembling structures needed for mitosis
  • 25. Chromosomes & Interphase
    • During interphase chromosomes cannot be distinguished under the light microscope
      • They appear as chromatin
    • At the start of mitosis, the chromatin thickens, and chromosomes become visible
  • 26. The Cell Cycle
    • The sequence of cell growth and division
    • The cell cycle can last several hours to several days
    • Can be affected by environmental factors, like temperature
    • Has 4 stages:
      • mitosis & division of cytoplasm ( cytokinesis )
      • The other 3 are part of interphase :
        • G1
        • S
        • G2
  • 27. Picturing the Cell Cycle
  • 28. G1 - Growth
    • After mitosis, a period of intense cellular activity and growth
    • The cell doubles in size
    • Enzyme production is high
    • Cells that stop growing remain in G1
  • 29. S- Synthesis
    •   Cells that divide enter S, or synthesis, phase
    •   The chromosomes replicate
  • 30. G2 – Further Growth
    • A second period of growth
    • Structures used in mitosis are assembled
  • 31. The Phases of Mitosis
    • Mitosis is actually a continuous process
    • But we divide it into 4 phases:
      • Prophase
      • Metaphase
      • Anaphase
      • Telophase
  • 32. Prophase
    • 60% of the period of mitosis is prophase
    • Divided into 3 parts: early, middle, & late
    • Chromosomes begin to coil into short rods
    • Nucleoli break down & begin to disappear
    • 2 pairs of dark spots called centrosomes appear outside the nuclear membrane
      • In animal cells, the centrosomes contain centrioles , formed from microtubules
      • Plant cells have no centrioles
    • The centrosomes move to opposite sides of the cell
  • 33. Mid Prophase
    • At the beginning of mid-prophase spindle fibers form between the centrioles
    • Additional fibers radiating out from each centriole form the aster
    • The nuclear membrane has broken down and disappeared
  • 34. The Mitotic Spindle
    • Spindle fibers made of microtubules radiate from the centrosomes
    • This array of spindle fibers = the mitotic spindle
    • 2 types of spindle fibers:
    • Kinetechore fibers
      • Attach to a disk-shaped protein called a kinetecore
      • Found in the centromere of each chromosome
      • Extend from the kinetechore of each chromatid to one of the centrosomes
    • Polar fibers
      • Extend across the dividing cell from one centrosome to the other
  • 35.  
  • 36. Late Prophase
    • The centrosome pairs are at opposite ends of the cell
    • The centosomes are fully formed
    • Chromosomes are attached to the centrosomes by spindle fibers
    • Other spindle fibers stretch across the cell from one centriole to the other
  • 37.  
  • 38. Metaphase
    • The chromosomes are pushed and pulled by spindle fibers along cell's the midplane
      • called the equator
  • 39. Anaphase
    • Begins with the separation of chromatids in each chromosome
    • Spindle fibers appear to shorten, pulling the chromatids apart at the centomere
    • Each chromatid is now a chromosome
    • 2 sets of separated chromosomes then move through the cytoplasm to opposite poles of the cell
  • 40.  
  • 41. Telophase
    • The last stage of mitosis
    • After the individual chromosomes have reached opposite poles of the cell, spindles disappear
    • A nuclear membrane forms around each set of chromosomes
    • Chromosomes return to a thread-like mass
    • Centrioles duplicate
      • 2 centrioles formed in each daughter cell
    • Nucleoli re-form within each newly formed nucleus
  • 42.  
  • 43. Cytokinesis
    • The division of the cytoplasm
    • Follows mitosis
    •   Cytokinesis begins during telophase
    • In animal cells, the cell membrane pinches together
    • The area that pinches in and separates is called the cleavage furrow
    • In plants, a cell plate is formed, dividing the two halves
  • 44. Picturing Cytokinesis
  • 45.  
  • 46.  
  • 47. Chromosome Number
    • Cells formed thru mitosis have the same number of chromosomes as the parent cells
    • If combined in sexual reproduction, the offspring would have 2x chromosomes!
    • Therefore gametes have only half the number of chromosomes of somatic cells
      • Gametes = sex cells
  • 48. Meiosis
    • Gametes need another process for nuclear division
    • Meiosis reduces the number of chromosomes to 1/2 the number in somatic cells
  • 49. Meiosis I & II
    • Forming haploid daughter cells from diploid parent cells requires two successive cell divisions:
      • First = Meiosis I –
        • homologous chromosomes separate
      • Second = Meiosis II
        • chromatids of each chromosome separate
  • 50. Meiosis I
    • Preceded by replication of DNA that forms the chromosome
    • Synapsis = pairing of homologous chromosomes
    • Each pair of homologous chromosomes twists around each other, forming a structure called a tetrad
    • Meiosis can be divided into same 4 phases as mitosis:
      • Prophase, Metaphase, Anaphase, Telophase
  • 51. Prophase I
    •   Chromatin begins to coil into short rods
    •   Homologous chromosomes are formed
    •   Spindle fibers appear
    •   Nucleoli break down
    • By the end, the nuclear membrane has dissolved, and tetrads are visible
  • 52. Crossing Over
    • During synapsis , (prophase I) the chromatids of homologous pairs twist around each other
    • A portion of one chromatid may break off and reattach, “trading” with the same piece from its homologous partner
    • The exchange of genes by reciprocal segments of homologous chromosomes during meiosis = “ crossing-over ”
  • 53.
    • Crossing over causes exchange of genetic material between maternal & paternal chromosomes
    • Results in genetic recombination
    • Genetic recombination is less likely in genes that are closer together.
  • 54. Chromosome Mapping
    • The likelihood that recombination will occur due to crossing-over depends on the genes’ distance from each other on the chromosome
    • Scientists can determine how frequently genes for particular traits occur together in offspring
    • This can be used to create a map of the chromosome
    • 1% recombination (crossing-over) = 1 map unit
  • 55. Metaphase I
    • Tetrads line up along the equator of the cell
    • Each tetrad becomes attached to spindle fibers
  • 56. Anaphase I
    • Homologous chromosomes that form each tetrad are pulled apart in pairs
    • One pair goes to one end of the cell, the other to opposite end
  • 57. Telophase I
    • Chromosomes reach ends of the cell
    • Cell divides into 2 daughter cells
  • 58.  
  • 59. Independent Assortment
    • During Anaphase I, one member of each homologous chromosome pair moves to one end of the cell, the other moves to the opposite end
    • The separation of homologous chromosomes is random
    • More, or fewer maternal (or paternal) chromosomes may end up on one side or the other
    • Each separation is independent of the others
    • This is the principal of independent assortment of chromosomes
    • Results in genetic variation
  • 60.  
  • 61. Meiosis I Summary
    • Meiosis I is a Reductive Division
    • It reduces the number of chromosomes from diploid "2n" to haploid "n"
  • 62. Meiosis II
    • Similar to mitosis but not preceded by replication of DNA
    • 4 Stages:
      • Prophase II
      • Metaphase II
      • Anaphase II
      • Telophase II
  • 63. Prophase II & Metaphase II
    • Prophase II
      • A new spindle forms around paired chromatids
    • Metaphase II
      • Chromosomes line up along the equator
      • They are attached at the centromere to spindle fibers
  • 64. Anaphase II
    • Centromeres duplicate & the chromatids separate
    • Resulting single chromatids move to opposite poles
    • Chromatids are now called chromosomes
  • 65. Telophase II
    •   A nuclear membrane forms around each set of chromosomes
    •   The spindle breaks down and cytokinesis occurs
    •   Result: 4 haploid daughter cells
  • 66.  
  • 67. Males vs. Females
    • In males, all 4 daughter cells differentiate to become sperm
    •   In females, the cytoplasm divides unevenly in Meiosis I
      • The smaller cell = first polar body
      • doesn't survive
    •   In Meiosis II, the division is again unequal
      • smaller half is second polar body
    • So only 1 of 4 daughter cells survives
      • rich in cytoplasm, has many nutrients to nourish the young organism
  • 68. Comparing Mitosis & Meiosis
    • MEIOSIS
    • 2
    • 4
    • diploid
    • haploid
    • different
    • MITOSIS
    • 1
    • 2
    • diploid
    • diploid
    • identical
    # of nuclear divisions: # of daughter cells: Parent cell type: Daughter cell type: Genetic likeness to parent:
  • 69.  
  • 70. Control of Cell Division
    • Timing and rate of cell division varies in different cell types
    • Control of rate of division is critical
    • Some cells require regulatory substances to begin division = growth factors
  • 71. Effect of Growth Factors
  • 72. Effect of Density
    • Density of cells also effects the rate of division
    • Crowding inhibits cell division
  • 73. The Restriction Point
    • A crucial checkpoint occurs late in the G1 phase of the cell cycle
    • Point of decision to divide = restriction point
    • Cell cannot turn back after this point
    • If it is “yes,” cell goes to S phase and copies DNA
    • If “no,” it goes to non-dividing state (G 0 )
      • Most cells are in G 0
  • 74. MPF
    • After S, the cell will enter G2
    • The “OK” signal that causes the cell to proceed from G2 to mitosis = mitosis promoting factor (MPF)
      • A complex of proteins
    • MPF is an enzyme
      • Protein kinase
  • 75. Abnormal Cell Division
    • Cancer cells do not respond normally to the body’s control mechanisms for cell division
    • Cancer cells divide excessively
    • Can invade other body tissues
    • When a cell divides abnormally = transformed
    • Abnormal cells are usually destroyed by the immune system
  • 76. Cancer
    • If abnormal cells are not destroyed and reproduce, they may form a mass of abnormal cells = tumor
      • Benign tumor = abnormal cells remain at the original site
      • Malignant tumor = cells spread to other parts of the body
    • Metastasis = spread of cancer cells in the body
  • 77. Breast Cancer Cell