In the standard Gubler and Hoffman method for double-stranded cDNA synthesis, the first strand is synthesized from mRNA by reverse transcriptase (such as AMV-RT or M-MuLV RT). RNase H specifically cleaves the phosphodiester bonds of the RNA strand in an RNA:DNA hybrid, generating small RNA fragments. These residual RNA fragments act as primers for E. coli DNA polymerase I to synthesize the second cDNA strand via nick-translation, after which DNA ligase seals any remaining nicks.

According to Beer-Lambert's law, nucleic acids absorb ultraviolet light maximally at $260 \text{ nm}$ due to the conjugated ring systems of purine and pyrimidine bases. By standard convention:
$1.0 \; A_{260} \text{ unit} = 50 \; \mu\text{g/mL}$ for double-stranded DNA (dsDNA)
$1.0 \; A_{260} \text{ unit} = 40 \; \mu\text{g/mL}$ for single-stranded RNA (ssRNA)
$1.0 \; A_{260} \text{ unit} = 33 \; \mu\text{g/mL}$ for single-stranded oligonucleotides/ssDNA.

A standard PCR thermal cycle consists of three fundamental steps:

• Denaturation: Carried out at the highest temperature ($94^\circ\text{C} - 98^\circ\text{C}$) to disrupt inter-strand hydrogen bonds and melt double-stranded DNA into single strands.
• Annealing: Carried out at the lowest temperature ($50^\circ\text{C} - 65^\circ\text{C}$, typically $3 - 5^\circ\text{C}$ below the primer Tm) to permit oligonucleotide primers to bind complementary sequences.
• Extension/Elongation: Operated at $72^\circ\text{C}$, the enzymatic optimum for thermostable Taq DNA polymerase.