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Joseph M. Steinberger

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 '''Molecular Tour:'''
-The <scene name='58/585079/1u3d_magnet/19'>cryptochrome protein</scene> obsorbs a single photon of blue light of 2.7 eV which excites an <scene name='58/585079/1u3d_magnet/2'>FAD ligand</scene>. FAD (at the atoms involved in resonance; shown with halos) is protonated by a <scene name='58/585079/1u3d_magnet/15'>nearby aspartic amino acid</scene> (the proximate donors shown with halos), and the electron hole is filled through a series of electron transfers - a chain reaction - involving three tryptophan amino acids (the nitrogen donors shown with halos). Notably, as seen in this alternative view, FAD and the three tryptophans  <scene name='58/585079/1u3d_magnet/21'>form a chain</scene> from the protein's inside to its outside. At this stage, where FAD is in its active signalling state, the extra electron on FAD and lone electron on the final tryptophan amino acid (324) <scene name='58/585079/1u3d_magnet/18'>have formed a radical pair</scene> (location of the electrons shown with halos). The pair is entangled, such that they spin in opposite or same directions. But only when they spin in the opposite directions, can the extra electron on FAD tunnel back to the hole left in tryptophan 324.
+First, the <scene name='58/585079/1u3d_magnet/19'>cryptochrome protein</scene> absorbs a single photon of blue light of 2.7 eV, exciting either of the FAD ligand's two nitrogen atoms, because they are involved in resonance (and shown in halos, as are the <scene name='58/585079/1u3d_magnet/24'>all the relevant atoms</scene>. This FAD nitrogen atom is protonated by a nearby aspartic amino acid (the proximate donors shown with halos), and the electron hole is filled through a series of electron transfers - first by the adjacent carbon atom in FAD (shown with a halo), and then in sequence the three tryptophan amino acids (the nitrogen donors shown with halos). Notably, as seen in this alternative view, FAD and the three tryptophans  <scene name='58/585079/1u3d_magnet/21'>form a chain</scene> from the protein's inside to its outside. At this stage, where FAD is in its active signaling state, the extra electron on FAD and lone electron on the final tryptophan amino acid (324) <scene name='58/585079/1u3d_magnet/18'>have formed a radical pair</scene> (location of the electrons shown with halos). The pair is entangled, such that they spin in opposite or same directions. But only when they spin in the opposite directions, can the extra electron on FAD tunnel back to the hole left in tryptophan 324.
 Researchers Klaus Schulten at University Illinois at Urbana Champaign and Ilya Solov'yov, now at the University of Southern Denmark, connect this system to the fascinating ability of many birds, and other flying species, to migrate while sensing the earth's magnetic field. Through simulations, they show that where the bird's cryptochrome compass's <scene name='58/585079/1u3d_magnet/23'>"FAD-trp324 needle"</scene> (shown as a dotted line) is aligned with the line  extending between the earth's poles, the entangled electrons will 'on average' spend more time in the same spinning state (also known as triplet; or parallel), and therefore by delaying the electrons return to trp324, FAD will 'on average' be in its signalling mode for longer.