Living Lab Cases: White Corn, Cool Ears and Nylon-Eating Bacteria

Three Cases in the Living Lab

1The Living Lab is a gallery in the Tillbury Museum of Natural History where visitors watch real experiments with plants, animals and microbes. Museum educator Mr. Ravindra Sethi starts every tour the same way. A gene is a section of DNA that carries the instructions for building a protein. Each protein has a shape that lets it do its job, and many proteins are enzymes, which speed up chemical reactions in cells. A mutation is a change in the DNA of a gene. Some mutations change the shape of a protein and how well it works, while others leave the protein just as it was.

2Case 1 is a tray of young corn plants under grow lights. Most of the seedlings are green, but a few are white. The white seedlings carry a mutation in a gene for a protein the plant needs to make chlorophyll, the green pigment that captures light energy for photosynthesis. Each corn seed holds a supply of stored food that feeds the young plant during its first days. Museum staff planted 40 green and 40 white seedlings in the same tray and tracked them for 20 days, as shown in Table 1.

3Case 2 is a pair of Himalayan rabbits. Their fur is white on most of the body but dark on the ears, nose, feet and tail. Dark fur color comes from an enzyme that makes dark pigment in growing hair. Himalayan rabbits carry a mutation that changes the shape of this enzyme, so it works well only in cool skin. Table 2 compares the changed enzyme with the typical enzyme of an all-dark rabbit. Hair grows in dark where the enzyme works at more than about half of the typical enzyme's best rate, and white where it works at less than about a fifth. In a room at 20 °C, the skin of the rabbits' ears is about 27 °C, their paws about 29 °C and their back about 36 °C. In a classic experiment, scientists shaved a patch of fur on a Himalayan rabbit's back and kept the patch cool with an ice pack while the fur grew back. The new fur in that patch grew in dark.

4Case 3 is a glass case of bacteria in dishes. In the 1970s, scientists studying ponds of waste water from a nylon factory found bacteria that could break down small pieces of nylon left over from making it. Nylon was invented in the 1930s, so those leftovers had not existed for very long. Changes in the bacteria's genes gave one of their enzymes a new shape that fits the nylon pieces. The museum grew a typical strain and a nylon strain of the bacteria, starting with 1 million cells in each dish. Table 3 shows the results after two days.