Benchwork, experimentation in the lab
3 class periods, including AT LEAST 72 hours for incubation
Main question explored: In what ways do cells respond to their environment?
The exploration of the genetic control of networks begins as students go into the laboratory to test how gene expression in Halobacterium changes in response to environmental conditions. Surprisingly, students observe that the cells, typically pink in color, experience a phenotypic change when grown in the presence of a full spectrum light bulb and when grown in the absence of all light. The cells grown in dark conditions turn nearly white, whereas cells grown in the presence of light turn a deep purple color.
Students also notice that the amount of cell growth increases when a full-spectrum light bulb is used. After learning that bacteriorhodopsin (bR), a protein found in the Halobacterium membrane, is purple, students begin to suspect that the genes for bR might be turned on in the presence of light and turned off in the absence of light. After gathering and graphing all of the class data using Excel, they induce that as the amount of light increases, so does the amount of bR. However, they find they do not have enough information to verify this, which sends them in search of more evidence to answer the question, “How might Halobacterium cells change the amount of bR in response to light?”