The DNA molecule from a single human chromosome is about 4 cm long and the length of DNA in an individual is about 200 times the distance from the earth to the sun. Isolated DNA in a test tube is also a long, stiff molecule. When alcohol is added to a DNA solution, the DNA fibers precipitate and can be spooled onto a glass rod. This feature of DNA is illustrated in the exercise, which provides enough purified DNA for 16 students working in pairs to perform the experiment.
Students isolate nuclei from calf thymus tissue and examine them microscopically. The DNA is then extracted from the nuclei by a simple procedure that uses a detergent and alcohol. Microscopes and a small centrifuge are desirable but not absolutely necessary for the exercise.
Cell respiration can be viewed as a series of enzyme catalyzed reactions in which carbohydrates, proteins, and fats are broken down to carbon dioxide and water with the release of energy. During the process, hydrogen is removed from the fuel molecules and oxygen is consumed. With this background information, students measure oxygen consumption and hydrogen liberation in germinating barley at different temperatures. The program provides eight calibrated respirometers for measurement of oxygen consumption and the chemicals required to perform a graphic dye reduction assay.
Acid phosphatase is present in many plant tissues where it catalyzes the removal of phosphate groups from macromolecules at low pH. In this exercise, students prepare a cell-free extract from wheat germ and determine the amount of the enzyme present in the extract. The experiment offers practical experience with enzyme extraction procedures and is an excellent introduction to the analysis of enzyme activity and basic enzyme kinetics.
A colorimeter is desirable but not absolutely necessary for this exercise.
The emission of light by living organisms is a fascinating process. The genetic system required for luminescence in the bacterium Photobacterium (Vibiro) fischeri is the lux operon. This operon contains a gene for luciferase (the enzyme that catalyzes the light-emitting reaction) and genes for enzymes which produce the luciferins (which are the substrates for the light-emitting reaction.). In this exercise, students create a luminescent population of bacteria by introducing into E.coli a plasmid that contains this lux operon.