Which of the following qPCR probe systems utilizes a unimolecular stem-loop structure?
Scorpion primers represent a unified primer-probe system where a specific probe sequence with fluorophore and quencher is covalently tethered to the 5' end of a PCR primer via a non-amplifiable linker. The probe adopts a stem-loop conformation, maintaining quenching in unbound state. After extension of the attached primer, the probe region intramolecularly hybridizes to the newly synthesized target within the same strand. This unimolecular probing mechanism improves kinetics, specificity and signal-to-noise compared to bimolecular probes. SYBR Green intercalates nonspecifically and lacks stem-loop architecture, while TaqMan is linear and cleaved rather than hairpin-based.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.