The Cell Cycle and Mitosis

• The cell cycle has two main phases

  interphase and mitotic phase

  
• Interphase


  -Growth and preparation for division

  - G1, S, G2

  
• Mitotic phase


  M phase and Cytokinesis

  
• M phase (mitotic phase)


  Division of replicated chromosomes
• Cytokinesis (mitotic phase)


  Separation into two cells
• Most of the cell cycle is spent in what stage?

  Interphase

  
• Interphase has 3 parts


  G1, S, G2
• G1 phase of interphase


  -Recovery from previous division

  - Cell doubles its organelles and grows larger

  - Accumulates raw materials for DNA synthesis
• S phase of interphase


  -DNA replication (synthesis)

  - Chromosomes enter with 1 chromatid each

  - Chromosomes leave with 2 identical chromatids each
• G2 phase of interphase


  - Between DNA replication and onset of mitosis

  - Cell synthesizes proteins necessary for division
• What is the G0 phase?


  - Some cells cannot complete mitosis

  - Cell division is ARRESTED, can be temporary or permanent

  - These cells cannot copy themselves but they do perform their normal functions

  - No repair possible

  a.) Muscle cells

  b.) Neurons

  
  

  - Cells will only commit to division if they have the right nutrients to complete the process

  a.) Starving cells will go into G0 phase

  
• Mitosis is divided into 4 phases

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Prophase (mitosis)


  - Chromatin condenses to form chromosomes

  - Nuclear membrane breaks down; Centrioles Double

  
• Metaphase (mitosis)


  Chromosomes attached to spindle fibers and migrates to align in center
• Anaphase (Mitosis)


  Sister chromatids are pulled apart to opposite poles(one chromosome each) by shortening spindle fibers

  
• Telophase/Cytokinesis (Mitosis)


  cytoplasm divides forming two genetically identical cells

  
• Mitosis


  - Spindle fibers are connected to centrioles and asters in animal cells

  - Centrioles are not present in plant cells, use a different mechanism

  
• Cytokinesis


  -In animal cells, the daughter cells are divided by a division furrow

  - In plant cells, cellulose produced in specialized vesicles to form a cell plate

  
• Fertilization


  when the egg and the sperm fuse together to form a zygote, which then divides

  
• identical(monozygotic) vs fraternal(dizygotic) twins

  
• Mitosis is important for cloning of animals. How?


  - Start with a diploid cell, but eggs are haploid

  - So a nucleus is taken out of a diploid cell and put into an unfertilized egg

  - It is then put in a uterus to grow