Practice question

In Scorpion chemistry, the primer and probing element are joined by a PCR blocker, typically hexethylene glycol, which halts DNA polymerase progression. During amplification, Taq polymerase extends the primer but is arrested at the blocker, thereby preventing synthesis through the probe sequence. This preservation is critical because copying the probe would destroy its stem-loop signaling capability and prevent intramolecular hybridization to the extension product. High GC content or hairpin stability alone cannot block enzymatic read-through, and quencher merely modulates fluorescence. The blocker thus maintains functional separation between amplification and probing domains within a single molecule.