Final answer:
Isopropanol is used in Buffer PB for the denaturation of proteins bound to DNA, and ethanol is used in Buffer PE to elute DNA off the purification column.
Step-by-step explanation:
The main purpose of isopropanol in Buffer PB is the denaturation of proteins bound to DNA. Meanwhile, ethanol in Buffer PE has a different role—its primary use is for eluting DNA off the column during the DNA purification process.
Isopropanol helps to denature proteins that may be bound to the DNA, ensuring that these proteins do not interfere with the DNA's subsequent analysis or applications. Ethanol is used later in the process to wash away any remaining salts and impurities, ultimately leading to the elution of purified DNA from the column. This is a critical step in plasmid DNA or genomic DNA purification protocols.