2.6 cell division

• Cell division in eukaryotic cells is either mitosis or meiosis
• Prokaryotic cells replicate by binary fission, not mitosis
• Viruses replicate inside the host cells they have invaded by injecting their nucleic acid into the cell
• The cell cycle


  1. Interphase (G1, S, G2)

  2. Nuclear division (mitosis or meiosis)

  3. Cytokinesis
• Interphase


  • Organelles double, cell grows in size, in preparation for cell division
• S phase


  • DNA replication happens
• G2 phase

  • DNA is checked for mutations, cell is destroyed if mutations detected
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Mitosis involves one round of cell division, resulting in two genetically identical diploid cells
• Purpose of mitosis


  Growth and repair, e.g. clonal expansion and differentiation of B cells in the humoral immune response
• Prophase


  • Chromosomes condense and become visible, centrosomes move to opposite poles, nuclear envelope disintegrates
• Metaphase


  • Chromosomes align along the equator of the cell (metaphase plate), spindle fibers attach to centromeres and chromatids
• Anaphase


  • Spindle fibers retract, pulling chromatids to opposite poles, requires ATP
• Telophase


  • Chromosomes become longer and thinner, spindle fibers disintegrate, nuclear envelope reforms
• Mitotic index


  Ratio of cells in mitosis to total number of cells in a field of view
• To calculate mitotic index, divide number of cells in mitosis by total number of cells in one field of view
• what stages of mitosis is this?

  .

  A) prophase

  B) metaphase

  C) anaphase

  D) telophase

  
• Meiosis


  A type of cell division (sexual reproduction)
• Types of cell division


  • Mitosis
  • Meiosis
• Mitosis


  Cell division that helps us grow and repair any damaged tissues and bacteria and another organisms will reduce mitosis as asexual reproduction to make more of themselves
• Meiosis


  Cell division that happens in the reproductive system in sexual reproduction, it makes gametes which are haploid cells like sperm and egg cells who allow them to fuse and fertilization to make a new organism
• Chromosome


  • Made up of two sister chromatids connected by a centromere
  • Centrioles form spindle fibres to move chromosomes, different from centromere
• Meiosis 1 and 2

  Meiosis 2 is similar to mitosis
• Genetic variation in meiosis


  • Crossing over
  • Independent assortment of homologous chromosomes
  • Independent assortment of sister chromatids
• Normal human cell has 46 chromosomes (23 pairs)
• Millions of possible genetic combinations can arise from meiosis due to crossing over and independent assortment
• what is a zygote?

  Fertilized egg.
• why is the type of nuclear division in a zygote is mitosis and not meiosis?
• what is a unipotent stem cell?

  A unipotent stem cell is a type of stem cell that has the ability to differentiate into only one type of specialized cell.
• what is a pluripotent stem cell?


  A pluripotent stem cell is a type of stem cell that has the ability to differentiate into any type of cell in the body.
• what is a totipotent stem cell?


  A totipotent stem cell is a cell that has the ability to differentiate into any type of cell in the body, as well as extraembryonic cells that form the placenta.