cell cycle and mitosis

• the cell cycle 


  consists of a period of cell growth and DNA replication called interphase

  and a period of of cell division called the M stage which involves both mitosis and cytokinesis
• checkpoints

  the cell cycle is regulated by checkpoints

  these occur at key points to make sure it's ok for the process to continue

  A) gap phase 1

  B) G1 checkpoint

  C) synthesis

  D) gap phase 2

  E) G2 checkpoint

  F) M phase

  
• interphase


  the cell carries out normal functions, but also prepares to divide

  the cell's DNA is unravelled and replicated, to double its genetic content

  the organelles are also replicated so it has spare ones

  ATP content is increased
• mitosis


  the form of cell division that occurs during the cell cycle

  needed for the growth of multicellular organisms and repairing damaged tissues

  some animals, plants and fungi also use it to reproduce asexually

  mitosis is really one continuous process but is described as a series of division stages - prophase, metaphase, anaphase and telophase
• structure of chromosomes in mitosis


  as mitosis begins, the chromosomes are made of two strands joined together in the middle by a centromere

  the separate strands are called sister chromatids

  there are two strands because each chromosome has already made an identical copy of itself during interphase

  when mitosis is over, the chromatids end up as one-strand chromosomes in daughter cells
• prophase


  the chromosomes condense becoming shorter and fatter

  tiny bundles of proteins called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle

  the nuclear envelope breaks down and chromosomes lie free in the cytoplasm
• metaphase 


  the chromosome (each with two chromatids) line up along the middle of the cell (at the spindle equator) and become attached to the spindle by their centromere

  at the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle before mitosis can continue
• anaphase


  the centromeres divide, separating each pair of sister chromatids

  the spindles contract, pulling chromatids to opposite ends of the cell, centromere first
• telophase


  the chromatids reach the opposite poles on the spindle

  they uncoil and become long and thin again

  they're now called chromosomes again

  a nuclear envelope forms around each group of chromosomes, so there are now two nuclei
• cytokinesis


  the cytoplasm divides

  in animal cells, a cleavage furrow forms to divide the cell membrane

  there are now two genetically identical daughter cells that are genetically identical to the original cell and to each other

  usually begins in anaphase and ends in telophase

  separate process to mitosis