High School Biology-Chemistry SMILE Meeting
22 January 2002
Notes Prepared by Porter Johnson

Benjamin Stark (Biology Department, IIT)
Ben did these two miniteach presentations at this first class of the semester:

  1. The first started with a very simple demonstration.  A glass microscope slide was placed over a candle flame, and we watched attentively as the slide fogged, and then the fog disappeared.  We thought about what the fog was.  One suggestion was "steam", but steam is an invisible gas, and the fog was liquid water [H2O].
    We then asked how we could get liquid H2O from a burning candle.  There were several incorrect suggestions, and the actual answer is that  a chemical reaction occurs when the candle burns.
    2 CH2 + 3 O2 ® 2 H2O + 2 CO2
    The CH2 radical represents the hydrocarbon chain present in the candle, and the H2O represents the fog produced. The carbon dioxide [CO2] escapes as a gas, since it would require a temperature of less than -108F or -78C for condensation. The water initially condenses on the slide, since its temperature for condensation must be less than 212F or 100C. The heat of the flame causes the fog to evaporate and the slide to be warmed, so that water can no longer condense there.
    Using Tinker Toy type molecular models, we illustrated how the atoms are arranged in molecules such as H2O and CO2, and how they are rearranged by chemical reactions. It is this rearrangement of atoms in the burning candle that produces heat and light. We designate this with the following energy diagram
                      ^
                      |
         Increasing   |    2CH2 + 3O2 |   
            Energy    |               |
                      |               |
                      |               |  (heat and light released)
                      |               |
                      |              \ /  
                      |               |    2H2O + 2 CO2
                      | 
    
    
    Karlene Joseph [Lane Tech HS, Biology] then discussed how a very similar chemical reaction
    C6H12O6 + 6 O2 ® 6 H2O + 6 CO2
    gives living organisms energy. The compound C6H12O6 is glucose [simple sugar]. This overall reaction occurs in many small steps in biological systems, so that the energy can be harvested in small, useful "packets", rather than being released in a "lump" of heat or light.
  2. The second miniteach focussed on two ears of Indian Corn [the kind with multi-colored kernels].  Some of the kernels had homogeneous colors, whereas others were speckled or striped with different colors.
                   ...               \\   ||   //
                  .....               \\  ||  //  
                   ...                 \\ || //
                   ..                   \\||//  
                                         \\// 
                Speckled                Striped
    
    Such speckled or striped kernels helped Barbara McClintock discover "mobile genetic elements" or "jumping genes". She received the Nobel Prize in Medicine in 1983 for this discovery.  Each kernel is an individual embryo derived from a single cell.  The genes in such a progenitor cell can be set to give one color.  However, in a cell that is created after several cell divisions have occurred, a "jumping gene" can move and change the genetic makeup so as to change the color of that cell, and all cells subsequently derived from it.  This leads to a patch (speckle or stripe) of cells of the new color on the background of cells with the original color.  Here is a schematic to illustrate the process:
     0: cells of original color
     X:: cells of new color due to movement of jumping gene
    
                         Cell Divisions         
     0      00   00    000     000       00000                     "blob"
                    00      000    00000       000000
                            00X    00XXX       000000             
                                               XXXXXX                  
    original              jumping                                            speckled
    cell                  event                                               region
    
    See the websites http://www.ndsu.nodak.edu/instruct/mcclean/plsc431/transelem/trans1.htm and http://www.profiles.nlm.nih.gov/LL/Views/Exhibit/narrative/nobel.html.  

    1902-1992 Barbara McClintock. Though American botanist Barbara McClintock conducted the research that led to her discovery of mobile genetic elements in the 940s, it was not until decades later that scientists began to take her work seriously. McClintock experimented with variation in the colors of corn kernels on a single cob. She tracked pigmentation changes in the corn and observed through microscopic evidence that two transposable genes called "controlling elements" were influencing the corn's pigmentation according to where their ever-changing position was on the corn's chromosomes. Whichever enes became the genetic neighbors of these controlling elements in a given generation of corn accounted for the changes in pigmentation McClintock observed. In 1983, McClintock became the first female recipient of the Nobel Prize for Physiology or Medicine. Scientists today believe "jumping genes," or transposons, may be linked to some genetic disorders such as hemophilia, leukemia, and breast cancer, and may have played critical roles in human evolution.
    Source:   http://www.pbs.org/wgbh/nova/genome/her_mcc.html

Notes provided by Ben Stark