Question

In order to protect DNA from DNase, which of the following chemical is used during DNA extraction?

• A. EDTA
• B. DEPC
• C. EtOH
• D. CTAB

Hint:

To protect nucleic acids during extraction: 1. Use EDTA (chelates \(\text{Mg}^{2+}\)) to inhibit DNase during DNA extraction. 2. Use DEPC (alkylates histidine) to inhibit RNase during RNA extraction.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
During DNA extraction, cell lysis releases intracellular enzymes, including deoxyribonucleases (DNases).
DNases rapidly degrade DNA, so their enzymatic activity must be inhibited to preserve the integrity of the extracted genomic DNA.

Step 2: Detailed Explanation:
Most active DNases are metalloenzymes that require divalent cations, specifically magnesium (\(\text{Mg}^{2+}\)) and calcium (\(\text{Ca}^{2+}\)), as essential cofactors to bind and hydrolyze the phosphodiester backbone of DNA.
Mechanism of EDTA (Ethylenediaminetetraacetic acid):
EDTA is a powerful chelating agent that binds divalent cations with extremely high affinity, sequestering them into stable coordination complexes.
By adding EDTA to the extraction buffer:
- Free \(\text{Mg}^{2+}\) and \(\text{Ca}^{2+}\) ions are bound by EDTA.
- Deprived of these essential cofactors, DNases become completely inactive.
- This protects the extracted DNA from enzymatic cleavage.
Let us review other options:
DEPC (B): Inhibits RNases by modifying histidine residues, used in RNA extraction.
EtOH (C): Used to precipitate DNA.
CTAB (D): A cationic surfactant used to lyse plant cells and remove polysaccharides.
Therefore, EDTA is used to protect DNA from DNase.

Step 3: Final Answer:
EDTA is the chemical used to inhibit DNase activity by chelating divalent cations, corresponding to option (A).