Figure 34.5  Shape selectivity. The binding of a deoxyribonucleoside triphosphate (dNTP) to DNA polymerase induces a conformational change, generating a tight pocket for the base pair consisting of the dNTP and its partner on the template strand. Such a conformational change is possible only when the dNTP corresponds to the Watson–Crick partner of the template base. Only the part of the polymerase directly participating in nucleotide binding is displayed (yellow ribbons). The green ball represents the Mg2+ ion.