Biology: Cell Cycle / Mitosis

• An adult human contains an estimated 100 trillion cells and yet we start Life as a single cell
• An adult human contains an estimated 100 trillion cells and yet we start Life as a single cell
• Cell division in eukaryotic cells

  1. To grow, develop and repair tissue damage

  2. Accomplished by a series of well orchestrated steps called mitosis
• Every day our bodies must produce millions of skin cells to replace those lost through normal activity
• Cell division in eukaryotic cells

  1. Cell grows, develops, and repairs tissue damage

  2. Cell relies on cell division
• Each of these cells must have a complete complement of the genetic material prior to cell division
• Cell division is accomplished by a series of well orchestrated steps called mitosis
• Every day our bodies must produce millions of skin cells to replace those lost through normal activity
• Each of these cells must have a complete complement of the genetic material prior to cell division
• Cell division


  1. DNA replication

  2. Chromosomes condense

  3. Chromosomes form sister chromatids
• Cell division


  1. DNA replication so each daughter cell receives an exact copy

  2. Chromosomes condense in the nucleus

  3. DNA condenses by wrapping around cores of histone proteins forming nucleosomes

  4. Chromatin coils up further shortening and condensing the chromosome

  5. Replicated chromosomes are called sister chromatids
• Chromatin


  Beads on a string structure formed by DNA wrapped around cores of histone proteins
• Interphase


  • Cell spends a great deal of time in interphase and a very short period of time actually dividing
• Interphase


  • Cell spends a great deal of time in interphase and a very short period of time actually dividing
• Prophase


  1. Chromosomes condense and become visible as two sister chromatids

  2. Cytoskeleton disassembles as the spindle begins to form

  3. Centrioles migrate to opposite poles establishing the spindle apparatus

  4. Nuclear envelope breaks down

  5. Chromosomes attach to microtubules from each pole
• Prophase


  1. Chromosomes condense and become visible

  2. Cytoskeleton disassembles

  3. Spindle begins to form

  4. Nuclear envelope breaks down

  5. Chromosomes attach to microtubules
• Metaphase


  Chromosomes aligned at the equator of the cell (metaphase plate)
• Metaphase


  Chromosomes aligned at the equator of the cell (metaphase plate)
• Anaphase


  1. Proteins holding sister chromatids together degrade, freeing individual chromosomes

  2. Chromosomes pulled by their kinetochores to opposite poles
• Anaphase


  1. Proteins holding sister chromatids together degrade

  2. Chromosomes pulled to opposite poles
• Telophase


  1. Cleavage furrow forms

  2. Chromosomes decondense

  3. Nuclear envelope reforms

  4. Spindle apparatus disassembles
• Telophase


  1. Cleavage furrow forms in the center of the cell

  2. Chromosomes cluster at opposite poles and begin decondensing

  3. Nuclear envelope reforms

  4. Spindle apparatus disassembles
• Cytokinesis


  1. In animal cells, cleavage furrow extends to separate daughter cells

  2. In plant cells, cell plate forms to separate daughter cells
• Cell cycle checkpoints


  • G1/S checkpoint
  • G2/M checkpoint
  • Spindle checkpoint
• G1/S checkpoint


  Primary point where cell cycle continues or stops based on external signals and growth factors
• Cytokinesis


  1. In animal cells, cleavage furrow extends to separate daughter cells

  2. In plant cells, cell plate forms to separate daughter cells
• G2/M checkpoint


  Allows cells that have successfully completed interphase to begin mitosis
• Cell cycle checkpoints


  • G1/S checkpoint
  • G2/M checkpoint
  • Spindle checkpoint
• Spindle checkpoint


  Ensures all chromosomes have attached to the spindle before anaphase
• G1/S checkpoint


  Primary point at which the cell cycle continues or stops based on external signals and growth factors
• Factors affecting cell cycle regulation

  • Growth factors
  • Cell size
  • Nutritional state
• G2/M checkpoint


  Allows cells that have successfully completed interphase to begin mitosis
• From interphase to cytokinesis, the entire process of cell division can take on average 10 to 20 hours in a typical plant or animal cell
• Spindle checkpoint


  Ensures all chromosomes have attached to the spindle before anaphase
• The accuracy of mitosis and the consistency of the checkpoints during interphase ensure that most cells in a eukaryotic organism can produce identical copies of themselves
• Factors affecting cell cycle regulation

  • Growth factors
  • Cell size
  • Nutritional state
• This process allows for growth and repair to prolong overall physiology as well as life itself
• The entire process of cell division can take on average 10 to 20 hours in a typical plant or animal cell
• An adult human contains an estimated 100 trillion cells and yet we start Life as a single cell
• Cell division can happen at different frequencies, with skin cells having a high turnover rate and adult neurons/muscle cells rarely dividing