The Cell Cycle


The Stages of the Cell Cycle:

  • Interphase (G1, S and G2)
  • Nuclear Division (mitosis)
  • Cytokinesis

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Stage 1: Interphase

Interphase is the first phase of the cell cycle and is the longest phase. It is made up of the 1st Growth Phase, the Synthesis Phase and the 2nd Growth Phase. Interphase is sometimes known as the resting phase because no division actually takes place. At each stage in interphase there is a "checkpoint" to make sure that no mistakes are carried through to the next stage

1st Growth Phase (G1):

  • protein synthesis and organelle synthesis takes place
  • normal cell metabolism
  • Checkpoint: repair any damaged chromosomes

Synthesis Phase (S phase):

  • DNA replication takes place -> DNA is copied and proofread by DNA polymerase
  • Checkpoint: stop cycle if chromosomes haven't copied

2nd Growth Phase (G2):

  • More cytoplasm and proteins are produced (proteins needed for division)
  • Checkpoint: repair any damaged DNA
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Stage 2: Nuclear Division (aka mitosis)


  • DNA replicates and chromatin coils and condenses into a chromosome
  • Centrioles migrate to the poles


  • Nuclear envelope breaks down
  • Spindle fibres release and chromosomes line up on the equator
  • Centromere and spindle join


  • Chromatids split at the equator and they are pulled to opposite poles
  • Contacting/shortnening of the spindle


  • Nuclear envelope forms around 2 new nuclei
  • Chromatids change back into chromatin
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Stage 3: Cytokinesis

During cytokinesis, the cytoplasm of the parent cell divides to make 2 separate daughter cells

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