Bioluminescence

• The chemistry behind bioluminescence lies in a special molecule called luciferin. When luciferin reacts with another molecule, usually an enzyme called luciferase, in the presence of oxygen, energy is released. This energy takes the form of visible light, creating the characteristic glow. Different luciferins and luciferases determine the emitted light’s colour and intensity.
• Marine organisms including single-cell dinoflagellates, some jellyfish and the deep sea anglerfish use the luciferin-luciferase reaction to release energy as blue-green light.
• Terrestrial Organisms including fireflies and glowworms also use the luciferin-luciferase reaction to create light.
  • Fireflies have a specialized light organ that contains luciferin and luciferase. The reaction involves adenosine triphosphate to provide the energy to excite an electron in the luciferin, which then emits a photon upon returning to its ground state.

  • Glowworm larvae of various fly and beetle species possess luciferin and luciferase and produce a similar light-emitting reaction.

Materials Involved in Bioluminescence

• Luciferin: This small organic molecule acts as the fuel, with different variations depending on the organism. It’s the source of the chemical energy that gets converted into light.
• Luciferase: This enzyme acts as the catalyst, speeding up the reaction between luciferin and oxygen. Different luciferases determine the colour and intensity of the emitted light.
• Oxygen: Although not universally used, oxygen serves as the final electron acceptor in most bioluminescent reactions, stabilizing the energy released and enabling light emission.
• Adenosine Triphosphate (ATP): In some systems like fireflies, ATP provides the initial energy boost to excite the electron in luciferin, kicking off the bioluminescent reaction. However, in these systems, the excited electron ultimately interacts with oxygen as the final electron acceptor, similar to systems that use oxygen directly.

The Bioluminescent Process

• Excitation: The luciferase enzyme interacts with luciferin, either directly using energy from ATP (fireflies) or indirectly drawing energy from sunlight or chemical reactions with the organism (dinoflagellates). This interaction excites an electron in the luciferin molecule, raising its energy state.
• Electron Transfer to oxygen: In most bioluminescent reactions, the excited electron in the luciferin molecule doesn’t directly emit light. Instead, it transfers its energy through a series of steps, ultimately reaching oxygen as the final electron acceptor.
• Energy Release: During this transfer, some of the released energy is channelled into a specific form suitable for light emission. This specific energy then triggers the luciferin molecule to emit a photon (light).
• Light Emission: Upon releasing this converted energy as a photon (light), the excited molecule returns to its ground state.
• Variations: While the basic principle remains similar, specific molecules, reaction pathways, and light colours can vary significantly depending on the organism and its unique bioluminescent system.

Electron Excitation in Bioluminescence

• Imagine an electron within the luciferin molecule orbiting its nucleus, like a ball at the bottom of a hill. This is the ground state, where the electron has its lowest energy.
• During the bioluminescent reaction, the luciferin molecule receives energy from different sources depending on the organism:
  • Fireflies: The luciferase enzyme uses ATP to directly excite the electron, pushing it to a higher energy level.
  • Dinoflagellates: Light or chemical reactions interact with luciferin, indirectly causing electron excitation.
  • Once energized, the excited electron jumps to a higher energy level within the luciferin molecule. This excited state is unstable, and the electron wants to return to its ground state.
  • However, it doesn’t simply drop back down. Instead, in most bioluminescent organisms, it transfers its energy through a series of steps to oxygen, the final electron acceptor. The excited electron doesn’t physically jump to oxygen but interacts with it indirectly through the molecule chain, ultimately transferring its energy.
  • During this transfer, some of the released energy gets converted into a specific form suitable for light emission. Finally, this converted energy triggers the emission of a photon from the excited molecule (often luciferin itself), releasing the remaining energy and bringing the electron back to its ground state.