Knowledge-6 MACC

• Prokaryotic cells divide by binary fission
• mitosis is where a parent cell divides to produce two genetically identical daughter cells with the same number of chromosomes.
• meiosis is where a parent cell divides into four haploid cells which are not genetically identical and have different numbers of chromosomes to the parent.
• the stages of the cell cycle:

  1. Interphase- occupies most of the cell cycle and occurs in three step process.
  2. Nuclear division- the nucleus divides into two or four depending on the type of division occurring (mitosis or meiosis).
  3. Cell division- division of the cytoplasm known as cytokinesis, where the cell divides into two or four cells depending on type of division.
• Interphase 3-step process:

  1. G1 or gap phase one: proteins required for organelles are synthesized.
  2. synthesis phase: DNA replication takes place resulting in a doubling of the mass of DNA.
  3. G2 or gap phase two: organelles grow and divide , ATP levels increase.
• Interphase is know as the resting phase but the cell is very metabolically active, it also takes up the most time in the cell cycle.
• First gap phase= organelle synthesis and provision of biochemicals

  synthesis phase = DNA replication occurs

  Second gap phase = energy stores are increased
• Mitosis occurs in five stages which can be written as the acronym I.P.M.A.T where:

  • I = interphase
  • P = prophase
  • M = metaphase
  • A = anaphase
  • T = telephase
• Prophase process:

  • each chromosome thicken and shorten by supercoiling (each chromosome is two genetically identical sister chromatids joined by a centromere).
  • the nuclear envelope disappears.
  • the centrioles form a spindle network, separate and move to opposite poles of the cell.
• Metaphase process:

  • the chromosomes move to the equator of the cell.
  • the spindle fibers attach to the centromeres.
• Anaphase process:

  • the spindle fibers contract, separating the sister chromatids.
  • the individual chromatids are pulled towards poles , they are now essentially chromosomes.
• Telophase process:

  • a nuclear envelope appears around each set of chromatids to from two new nuclei.
  • the chromatids uncoil and the spindle fibers disintegrate.
  • the cell surface membrane starts to invaginate at the equator of the cell.
• How to find mitotic index:

  • mitotic index = number of cells in mitosis / number of cells observed
• cancer is the unregulated , uncontrolled rapid cell division which forms tumors which can then become cancerous.
• Many cancer treatments are directed at controlling the rate of cell division such as inhibiting spindle formation or preventing DNA replication.
• Chemotherapy drugs disrupt the cell cycle in all dividing cells but have a greater effect on rapidly dividing cells.
• Virus replication:

  Viruses are non-living and do not undergo cell division. instead they inject their nucleic acid (DNA or RNA) into a host cell. the infected host cell synthesizes viral nucleic acid and proteins and assembles virus particles.
• Binary fission:

  1. replication of circular DNA and of plasmids in the cytoplasm.
  2. division of the cytoplasm to produce two daughter cells, each with a single copy of circular DNA and a variable number of copies of any plasmids.