The Cell Cycle

• Cell Division


  Process by which a cell divides into 2 new cells
• Why cells need to divide

  • Living things grow by producing more cells, NOT because each cell increases in size
  • Repair of damaged tissue
• Parent cell


  The original cell
• Daughter cells


  2 new cells
• Before cell division occurs, the cell replicates (copies) all of its DNA, so each daughter cell gets complete set of genetic information from parent cell
• Each daughter cell is exactly like the parent cell – same kind and number of chromosomes as the original cell
• Many organisms, especially unicellular organisms, reproduce by means of cell division – called asexual reproduction – Ex: bacteria
• Nucleus


  The control center of the cell and is bound by a nuclear membrane. It contains the genetic material DNA that is replicated prior to cell division.
• Chromosome


  More efficient division
• Every organism has its own specific number of chromosomes
• All somatic (body) cells in an organism have the same kind and number of chromosomes
• Centrioles


  Minute cylindrical organelle arranged near the nucleus in animal cells. They are found in pairs and move towards the poles of the nucleus when it is time for cell division. They are also involved in the development of spindle fibers in cell division.
• Mitosis


  When body cells undergo a cell division. Somatic cells.
• Meiosis


  When sex cells undergo a cell division. Gametes (egg, sperm).
• Cell Cycle


  Series of events cells go through as they grow and divide. Cell grows, prepares for division, then divides to form 2 daughter cells – each of which then begins the cycle again.
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Prophase


  • Nuclear envelope breaks down
  • Nucleolus disappears
  • Duplicated centrioles begin to move in opposite poles and form spindle fibers between them
  • Chromatin fibers become visible as they condense, coil, and become shorter and thicker
• Metaphase


  • Chromosomes migrate randomly and line up toward the equator
  • Another checkpoint occurs at this stage
  • When a chromosome is not properly aligned at the mitotic spindle, mitosis will be arrested
  • As a result, of this checkpoint, sister chromatids do not separate until a complete set of chromosomes will be distributed to each new individual
• Anaphase


  • Sister chromatids separate and move towards the opposite ends
• Telophase


  • Nuclei forms in both poles as new nuclear membrane forms around the new nucleus
  • Nucleus reappears and spindle fibers begin to disappear
  • Division of cytoplasm (Cytokinesis) begins and is completed when the cell contents have been divided equally to the two daughter cells produced
• Meiosis


  • Production/formation of gametes
  • Basis of sexual reproduction
  • Only germ cells undergo meiosis
• Meiosis Leads to Genetic Diversity

  • 2 parents contribute ½ of genetic material to offspring
  • Crossing-over in prophase I
  • Chromosomal alignment in Metaphase I
• Meiosis produces cells that are NOT identical, unique gametes
• Prophase 


  phase of chromosome condensation
• Metaphase


  alignment
• Anaphase


  seperation
• Telophase


  Nuclear formation