Cell division, diversity and cellular organisation

• Mitosis


  Cell division process that produces two identical diploid daughter cells from one diploid parent cell
• Cell cycle

  1. Interphase (G1,S,G2)

  2. Mitotic phase (mitosis and cytokinesis)
• Interphase

  Cell increases energy stores, grows in size, replicates organelles and DNA
• Mitotic phase

  • Nucleus divides into two daughter nuclei (mitosis)
  • Cell divides into two daughter cells (cytokinesis)
• Mitosis is used for growth, repair, and asexual reproduction
• Interphase

  G1 is where proteins required for organelles are synthesised

  S is where DNA replication takes place resulting in the doubling of DNA mass (2n to 4n)

  G2 where organelles grow and divide and energy stores increase
• Regulation of cell cycle

  G1 checkpoint checks for

  • Cell size
  • Nutrients
  • Growth factors
  • DNA damage
• Regulation of cell cycle pt2

  Go is the resting state where damaged DNA cells go to either die or tries to repair itself to re enter the cell cycle.
• Regulation of cell cycle pt3

  G2 checkpoint checks for:

  • Cell size
  • DNA replication
  • DNA damage
• Regulation of cell cycle pt4

  Spindle assembly checkpoint checks for

  • The chromosomes to be attached to spindle
• Chromosomes are two genetically identical sister chromatids joined by the centromere
• Asexual reproduction

  • Fungi ( e.g. yeast) divide to produce two genetically identical daughter cells through budding
  • Some plants and insects can also use parthenogenesis to reproduce
• Cell division (mitosis pt1)

  The first stage is Prophase

  • Where the chromosomes shorten and thicken and become visible
  • The nuclear envelope disappears
  • Centrioles move to the poles of the cells and produce a network of spindle fibres between them
• Cell division ( mitosis pt2)

  The second stage is metaphase

  • The sister chromatids are moved to the equator of the the cell by the spindle fibres. This forms the metaphase plate.
  • Each chromosome is attached to a spindle fibres by its centromere
• Cell division ( mitosis pt3 )

  The third stage is anaphase

  • The spindle fibres pull apart the chromosomes into pairs of chromatids by the centromere
• Cell division ( mitosis pt4)

  The fourth stage of mitosis is telophase

  • Chromatids begin to uncoil
  • Nuclear envelope begins to develop
  • Spindle fibres break down
  • After, cytokinesis happens where the the cell splits into two daughter cells
• Cell division (meiosis pt1)

  The first stage of meiosis is Prophase |

  • Chromosomes condenses
  • Nuclear envelope disintegrates
  • Homologous chromosomes form bivalents
  • Crossing over occurs
• Meiosis

  Meiosis produces 4 genetically different daughter cells due to four reasons

  • Crossing over
  • Independent assortment
  • Mutations
  • Random fertilisation
• Crossing over (meiosis)

  Crossing over happens in Prophase | where the homologous chromosomes form bivalents so that non sister chromatids can cross over at the chiasmata and exchange sections of chromosomes with the same genes and different alleles
• Independent assortment

  During metaphase |, the homologous chromosomes are randomly distributed to the equator of the cell. As well as in metaphase ||, the sister chromatids are randomly distributed onto the equator of cell so the chromatids are randomly separated
• Cell division (meiosis pt2)

  The second stage is metaphase |

  • Bivalents line on the cell equator
  • Spindle fibres attach to centromeres
  • Independent assortment occurs
• Cell division (meiosis pt3)

  The third stage is anaphase |

  • Spindle fibres pull apart the homologous chromosomes to opposite poles of the cell
• Cell division (meiosis pt4)

  The fourth stage is telophase |

  • Nuclear envelope reforms around new nuclei
  • Chromosomes uncoil
  • The cell undergoes cytokinesis
• Cell division (meiosis pt5)

  The stage 2 of meiosis happens (2nd division) with the 1st phase is Prophase ||

  • Chromosomes recondensed
  • Nuclear envelope breaks down again
  • Spindle fibres reforms
• Cell division (meiosis pt6)

  The second stage of stage 2 meiosis is Metaphase ||

  • Chromosomes randomly arranged on the equator by the spindle fibres
  • And independent assortment occurs
• Cell division ( meiosis pt7)

  The third phase in stage 2 meiosis is Anaphase ||

  • Chromatids are pulled apart by the spindle fibres
  • Chromatids moved to the opposite poles of the cells
• Cell division (meiosis pt8)

  The last stage of stage 2 meiosis is Telophase ||

  • Chromatids uncoil
  • Nuclear envelope reforms
  • Cell undergoes cytokinesis
• Bivalents are a pair of homologous chromosomes
• Mitosis and Meiosis chromosomes number

  • For mitosis their chromosomes number turns to 2n to 4n and back to 2n
  • For meiosis their chromosomes number goes form 2n to 4n to 2n to n
• Stem cells

  Stem cells are cells that have not yet differentiated into specialised cells and can divide an unlimited number of times
• Stem cells pt2

  Genetically identical stem cells in bone marrow differentiate into erythrocytes (red blood cells) and neutrophils (white blood cells ). Neutrophils has a lobed nucleus and it's cytoplasm filled with lysosmes
• Stem cells pt3

  There are two sources of animal stem cells these are bone marrow and embryos
• Stem cells pt4

  There are three types of stem cells

  • Totipotent
  • Pluripotent
  • Multipotent
• Stem cells pt5

  Totipotent cells are found in embryonic tissues and can differentiate to produce any type of body cells
• Stem cells pt6

  Pluripotent are found in embryos and bone marrow and can differentiate into all tissue types
• Stem cells pt7

  Multipotent are found in umbilical cord and bone marrow and can only differentiate into a limited number of cell types
• Xylem and phloem

  Xylem vessels and phloem sieve tubes differentiate from plant meristems. Meristems are totipotent.
• Xylem and phloem pt2

  Lignin is deposited in the cell walls to strengthen and waterproof them.

  Meristems cells forming phloem differentiate into companion cells and sieve tubes elements
• Stem cells disadvantages

  • Transfer viral infections through the transplant
  • Ethical beliefs
• Erythrocytes are red blood cells