(b) X-Ray structure of the Schistosoma mansoni hammerhead ribozyme drawn in stick form with C atoms the colors indicated in Fig. 24-26a except that those of G-12 are light green and those of C-1.1 are light blue, N blue, O red, and P orange. Adjacent P atoms in the same strand are connected by thin orange rods. The P atom of the scissile phosphate group (bridging C-17 and C-1.1) and the nucleophile (O2' of C-17) are represented by small spheres. (c) The ribozyme's active site residues, which are drawn in stick form with C green, O red, N blue, and P orange. Hydrogen bonds are represented by dashed black lines. In the proposed reaction mechanism, the dotted black line marks the in-line trajectory taken by atom O2' of C-17 in nucleophilically attacking the P atom of C-1.1, the scissile phosphate group. [Based on an X-ray structure by William Scott, University of California at Santa Cruz. PDBid 2GOZ.]