the cell cycle

• Cell Cycle

  The life of a cell can be divided into three stages: Interphase, Mitosis, Cytokinesis

  
• Interphase(G1, S, G2)

  1. G1: cell grows and performs its roles

  2. S: DNA is duplicated (synthesis)

  3. G2: further growth and production of organelles/ preparation for mitosis

  
• Interphase(not phases)

  • Cells spend approx. 90% of their lives in this phase
  • During this stage the cell will grow, carry out cellular respiration (use energy) and basic life functions. Organelles are formed as well.
• Chromatin


  Long, thin strands of DNA
• DNA replication occurs in interphase
• The chromatin form is 'unwound' so it is easier to copy
• There needs to be 2 copies of the genetic content of the cell ready for mitosis to occur
• Mitosis

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

  
• Mitosis(not phases)

  • Division of the nucleus and DNA in a dividing cell
  • Results in 2 daughter cells that have identical DNA to each other and to the original parent cell

  
• Prophase

  1. DNA (chromatin) strands will shorten and coil (thicken) to form chromosomes

  2. Each chromosome consists of two identical strands called sister chromatids which are held together at the centromere

  3. Spindle fiber network starts to form from centrosomes

  4. Nuclear membrane starts to break down
• Metaphase

  The chromosomes line up along the middle of the cell along the equatorial plate of the spindle fiber network. Centromeres attach to fibres

  
• Anaphase

  1. Centromeres split and sister chromatids separate to form daughter chromosomes

  2. The daughter chromosomes are pulled to opposite ends of the cell by retracting spindle fibers

  
• Telophase

  1. Daughter chromosomes stretch out to form chromatin again and are no longer visible

  2. Nuclear membranes begin to reform around each group of daughter chromosomes (chromatin)

  3. Spindle fibers retract

  4. The cell appears to have two nucleii

  
• Cytokinesis

  1. Division of the cytoplasm and contents

  2. Animal cells: the cell membrane pinches off in the centre (cleavage furrow) to form 2 identical cells

  3. Plant cells: A cell plate forms between the two daughter cells to form a cell wall

  
• The cell will not divide if: neighbouring cells tell cell not to divide, not enough nutrients for cell growth, DNA in the nucleus has not been duplicated, DNA is damaged and not enough time to repair (the cell is then destroyed)