the cell cycle

• there are 3 stages to the cell cycle:

  • interphase
  • mitosis
  • cytokinesis
• a cell cycle is the stages a cell must go through as it grows and divides
• interphase is the longest stage for most cells
• interphase is the period where cell carries out life activities
• DNA in interphase are very long, thin, and invisible stands
• in interphase, DNA strands are copied to prepare for cell division
• mitosis is the division of the contents of the nucleus (DNA)
• cytokinesis is the division of the rest of the cell (cytoplasm, organelles, cell membrane)
• the four phases of mitosis

  • prophase
  • metaphase
  • anaphase
  • telophase
• every chromosome has two identical strands called sister chromatids
• in prophase, long strands of DNA condense into a compact form (visible under a microscope) referred to as chromosomes
• a centromere holds the chromatids together
• during prophase, nuclear membrane breaks down
• in metaphase, chromosomes line up in the middle of the cell
• in metaphase, spindle fibres form from centrioles and attach to centromeres
• in anaphase, the centromeres split
• in anaphase, sister chromatids (daughter chromosomes) separate and move to opposite sides of the cell
• in telophase, daughter chromosomes stretch out and are no longer visible
• in telophase, new nuclear membrane forms around each group of daughter chromosomes
• cytokinesis is the final stage of cell division
• in cytokinesis, cytoplasm divides and two genetically identical daughter cells are produced
• animal cells have a cleavage furrow, while plant cells have a cell plate
• checkpoints exist in the cell cycle:

  • proteins monitor cell activities and surroundings
  • messages are sent to the nucleus which then instructs the cell whether or not to divide
• When should a cell remain in interphase and NOT divide?

  • signals tell cell not to divide
  • lack of nutrients for cell growth
  • DNA has not been replicated
  • DNA is damaged