The core biochemical principle that protein structure determines protein function is illustrated by green fluorescent protein (GFP), which is an autofluorescent protein isolated from the Pacific Northwest jellyfish Aequorea victoria. GFP is a β-barrel protein containing in its interior its own chromophore (part of a molecule responsible for producing color). The chromophore forms spontaneously through a chemical reaction involving three amino acid residues in the GFP. Expression of the cloned GFP gene in most cells results in the emission of green light (~510 nm) after excitation with blue light (~470 nm). In other words, as long as the protein maintains its structure, it performs the same function, regardless of the organism from which it originates. The use of GFP as a fluorescent marker in live cells has allowed cell biologists and physiologists to study cellular processes in real time. Use of this technique has become an important part of experimental biochemistry and cell biology, leading to the awarding of the 2008 Nobel Prize in Chemistry to the three pioneers of this method.