# DBT JRF 2020 — Question 24

Exam: DBT JRF 2020 · Section: A · Topic: Molecular Biology · Difficulty: Hard

## Question

Single stranded DNA can be separated from double stranded DNA efficiently using

## Options

- **A.** hydrophobic interaction chromatography
- **B.** RP-HPLC
- **C.** urea PAGE
- **D.** hydroxyapatite chromatography

## Answer

Option D

## Explanation

Hydroxyapatite $[\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2]$ chromatography exploits differential adsorption of nucleic acids: dsDNA binds via both phosphate groups (to Ca²⁺ sites) and bases (to PO₄³⁻ sites) forming a stronger interaction, while ssDNA binds primarily through phosphate groups only. At low phosphate buffer concentrations (e.g. 10 mM NaH₂PO₄), ssDNA elutes while dsDNA remains bound. Increasing phosphate concentration (e.g. 400 mM) then elutes dsDNA. This differential affinity enables efficient separation of ssDNA from dsDNA, and is also used to separate RNA from DNA and dsDNA from ssDNA–dsDNA hybrids.

Source: https://mypyqbuddy.com/questions/single-stranded-dna-can-be-separated-from-double-6a05a8a02adafec4702931fe