Cell cycle

• Cell theory:

  • Every organism is composed of one or more cells.
  • Continuity of life arises from growth and division of single cells.
  • Cells only arise by the division of single cells.

  Specialized cells cannot divide.
• The cell cycle:

  • Growth ( duplicates everything)
  • Replace damaged cells
  • Not all cells can divide (e.g specialized)
  • Those that can undergo a regular cycle of divions separated by periods of cell growth.
• 3 stages of cell cycles:

  1. Interphase
  2. Nuclear division
  3. Cytokinesis
• The cell cycle:

  • Makes up 90% of the cell cycle.
  • Cell division does not occur
  • DNA unravels and replicates to double
  • After the DNA is replicated new proteins become attached to it.
  • The chromosomes now consist of 2 strands called sister chromatids - contain identical genetic information.
  • Joined by a centromere
  • These become visible under a light microscope only during mitosis.
  • Also organelles are replicated and ATP is increased.

  
• Nuclear division:

  • The nucleus divides into 2
  • The chromatids separate from each other and are redistributed as chromosomes in the nuclei of the 2 new daughter cells.
• Cytokinesis:

  • The cytoplasm divides to produce 2 new daughter cells.
• Chromosomes:

  • Genome- a cells genetic information
  • Human cells- 2 meters of DNA- All this has to be replicated before cell divisions.
  • DNA molecules are packaged into chromosomes.
  • Chromosomes are made up of chromatin (DNA/protein)
  • Non dividing cells- chromosome is in the form of a long thin chromatin fiber .
  • After each DNA replication replication the chromosomes condense.
  • Each chromatin fiber becomes densly coiled and folded making the chromosomes much shorter and thinker.