Cell Cycle and Mitosis

• Interphase


  Makes up 90% of the cell cycle, chromosomes are decondensed and distributed throughout the nucleus. Nucleus is visible under a light microscope but not its DNA. Consists of 3 stages: Gap 1 (G1), Synthesis (S) and Gap 2 (G2).
• Gap 1 (G1)


  The first stage of interphase in the cell cycle where the cell grows, increasing the amount of cell cytosol. Proteins required for DNA replication will be synthesised. Mitochondria and if chloroplast is present, they will divide. Towards the end of the stage, it will continue in the cycle or drop out, entering G0.
• Synthesis (S)


  The stage where the parent cell replicates its DNA; at the end of the S stage the parent cell contains two identical copies of its original DNA. If replication doesn't happen properly, the new cells may not function properly.
• Gap 2 (G2)


  The third stage of interphase where proteins like the microtubules of the spindle fibres are synthesised and the cell continues to grow in preparation for division. By the end of this stage, cell should have doubled its size.
• Checkpoints in Cell Cycle

  There are several checkpoints that function to ensure that the cycle is on track. Each checkpoint can detect a particular kind of error, if one has occurred then the cycle for that cell may be aborted or delayed. Checkpoints occur after G1, G2 and one during the metaphase stage of mitosis.
• G1 Checkpoint


  The DNA of the cell is checked and it it is found to be damaged or incomplete, the cell is stopped from continuing through the cell cycle. If the DNA is all good however, it will continue in the cell cycle and advance the 'S' stage.
• G2 checkpoint


  The replicated DNA of the cell is checked for completeness and lack of damage. If the cell passes this checkpoint, it can then advance to the mitosis stage of the cell cycle.
• M Checkpoint


  Occurs at the metaphase stage of mitosis. This check ensures that the sister chromatids are attached to the correct microtubules of the spindle and are pulled in opposite directions to different poles of the spindle. If an error is detected, the cell cycle is delayed until the error is fixed.
• Diploid (2n)


  2 complete sets of chromosomes which is 46 chromosomes total. E.g. Blood cell.
• Haploid(n)


  1 set of chromosomes which is 23 chromosomes total. E.g. Sperm, egg
• Labelling Chromosomes

  A) Chromosome

  B) Sister Chromatid

  C) Longer Arm

  D) Centromere

  E) Short Arm

  F) Telomere

  
• DNA is wrapped around proteins called histone.
• Spindle Fibres


  Clusters of microtubules that grow out from the centrioles at opposite ends of the a spindle.
• Spindle


  Fine protein fibres that form between the poles of a cell during mitosis and to which chromosomes become attached.
• Gap 0 (G0)


  The phase of the cell cycle during which a cell is neither dividing nor preparing to divide. During this period the cell performs regulatory and its basic cellular functions. The cell cycle typically refers to the process by which the cell can grow and repair itself.
• Kinetochore


  A special attachment site of a chromatid by which it links to a spindle fibre.
• Centrioles


  A pair of small cylindrical organelles, used in spindle development in animal cells during cell division.