Multiple choice

DNA also exists as modified structure known as a triple helical DNA. Which of the following does not apply to this modified form of DNA?

  1. It is formed at neutral or acidic pH although being rare.

  2. It is triple-stranded.

  3. It requires Hoogsteen hydrogen bonding only.

  4. It requires Watson-Crick hydrogen bonding.
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A Correct answer
Explanation

A triple-stranded DNA is a structure of DNA in which three oligonucleotides wind around each other and form a triple helix. One strand binds to a B-form DNA double helix through Hoogsteen or reversed Hoogsteen hydrogen bonds. The triple helix is a partial binding to one of the strands, where the other strand maintains the Watson-Crick pairing. The formation of triple helix is favoured when there are stretches of oligopurines/pyrimidines in a DNA.

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