Cetyl trimethyl ammonium bromide (CTAB) method is a key technique in molecular biology for precipitating nucleic acids from complex samples like plant tissues. This SEO-optimized article solves the given MCQ in detail, explains each option, and covers the science behind CTAB.

Correct Answer

The CTAB method is generally used for precipitating nucleic acids. This cationic detergent selectively binds and precipitates DNA/RNA from contaminants in low-salt conditions, making it ideal for plant and fungal samples rich in polysaccharides.

Option Explanations

• Precipitating nucleic acids: Correct. CTAB forms insoluble complexes with nucleic acids at low salt (<0.5 M NaCl), allowing separation from soluble proteins and neutral polysaccharides. Nucleic acids are later solubilized at high salt and alcohol-precipitated for purification.

• Precipitating protein: Incorrect. CTAB does not primarily target proteins; it removes them via chloroform extraction or keeps them soluble during nucleic acid precipitation. Proteins are handled separately in the protocol.

• Precipitating neutral polysaccharides: Incorrect. In high salt (>0.7 M NaCl), CTAB precipitates acidic polysaccharides and debris, but neutral polysaccharides stay soluble. This differential precipitation protects nucleic acids.

• Lipids: Incorrect. Lipids are extracted into the organic phase (e.g., chloroform) early in the protocol, not precipitated by CTAB. CTAB focuses on nucleic acid isolation from polar contaminants.

CTAB Method Principle

CTAB (cetyltrimethylammonium bromide) is a cationic surfactant used in nucleic acid extraction. In low-salt buffers, it binds negatively charged phosphate groups on DNA/RNA, forming insoluble CTAB-nucleic acid complexes that precipitate by centrifugation. High salt reverses this for contaminants like polysaccharides, while alcohol (isopropanol/ethanol) finalizes nucleic acid recovery.

Key steps include cell lysis with CTAB buffer, chloroform extraction for proteins/lipids, salt-based precipitation, and ethanol wash.

Why CTAB Excels

This method shines for challenging samples (plants, fungi) with PCR inhibitors like polysaccharides and phenolics. Modifications make it faster and kit-free, yielding high-purity DNA for PCR, sequencing, or cloning. For life science students, mastering CTAB aids exam prep in molecular biology and biochemistry.