Thursday, August 18, 2011

Firefly Bioluminescence

Fireflies Exhibit a Unique Use of Energy. ATP is used to create flashes of light as energy is transferred to an electron in a specialized molecule called luciferin. The energy is released as light as the electron drops back to its original position

Photosynthesis transforms light energy into chemical energy. In bioluminescence, the reverse can happen—chemical energy is converted into light energy. Bioluminescence is common in the oceans, where hordes of glowing microscopic organisms called dinoflagellates lend an eerie bluish cast to fishes, dolphins or even ships that interrupt their movement.

More familiar, perhaps, is the glow of a firefly’s abdomen in the late summer. More than 1,900 species of fireflies are known, and members of each use a distinctive repertoire of light signals to attract a mate. Typically, flying males emit pattern a flashes. Wingless female, called glowworms, usually are on leaves, where they emit light in response to the male. In one species, Photuris versicolor, the female emits the mating signal of another species and then eats the tricked male who approaches her. Some frogs consume so many fireflies that they glow!

In the 1960s, johns Hopkins University researchers William McElroy and Marlene DeLuca asked Baltimore schoolchildren to bring them jar of fireflies. They then used the insects to decipher the firely bioluminescence reaction. McElroy and DeLuca found that light is emitted when a molecule called luciferin reacts with ATP, yielding the intermediate compound luciferin adenylate (figure). The enzyme luciferase then catalyzes reaction of the intermediate with molecular oxygen (O2) to yield Iaxyluciferin- and a flash of light. Oxyluciferin is then reduced to luciferin, and the cycle starts over.

Chemical companies sell luciferin and luciferase, which researchers use to detect ATP. When ATP appears in a sample of any substance, it indicates the presence of an organism. For example, the manufacturers of Coca-Cola use firefly luciferin and luciferase to detect bacteria in syrups used to produce the beverages. Contaminated syrups glow in the presence of luciferinand luciferase because the ATP in the bacteria sets the bioluminescence reaction into motion. Firefly luciferin and luciferase were also aboard the Viking spacecraft sent to Mars. Scientists sent the compounds to detect possible life—a method that would only succeed if Martian life-forms use ATP.

Although we understand the biochemistry of the firefly’s glow, the ways animas use their bioluminescence are still very much a mystery. This is particularly true for the bioluminescent synchrony seen in fireflies in the same trees. When night falls, first one firefly, then another, then another, then more, begin flashing from the tree. Soon the tree twinkles like a Christmas tree. But then, order slowly descends. In small parts of the tree, the lights begin to blink on and off together. The synchrony spreads. A half-hour later, the entire tree seems to blink on and off every second. Biologists studying animal behavior have joined mathematicians studying order to try to figure out just what the fireflies are doing—or saying—when they synchronize their glow.


Life, Sixth Edition Published by McGraw-Hill 2007