Practice question

Single-stranded nucleic acids form intramolecular secondary structures via base pairing that alter electrophoretic mobility independent of length. Denaturing agents prevent renaturation. Urea at 6 to 8 M concentration disrupts hydrogen bonding and base stacking, maintaining RNA and denatured DNA as extended random coils. It is compatible with polyacrylamide electrophoresis for sequencing gels. TEMED catalyzes polymerization, sucrose increases density, and bromocresol green is a tracking dye. Formaldehyde and formamide serve similar purposes, but urea is the standard denaturant for ssDNA and RNA gels.