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Biology · 2025 · 2 marks
CBSE 2025 · Region 6 · Set 2 · Q17
Study the given molecular structure of double-stranded polynucleotide chain of DNA and answer the questions that follow. (a) How many phosphodiester…
Study the given molecular structure of double-stranded polynucleotide chain of DNA and answer the questions that follow.
(a)
How many phosphodiester bonds are present in the given double-stranded polynucleotide chain ?
(b)
How many base pairs are there in each helical turn of double helix structure of DNA ? Also write the distance between a base pair in a helix.
(c)
In addition to H-bonds, what confers additional stability to the helical structure of DNA ?
Marking-scheme solution
(a)
six
(b)
• $\displaystyle 10$
• 0.34nm/$\displaystyle 3.4$ Ao
(c)
The plane of one base pair stack over the other in double helix additionally
confirms stability of helical structure of DNA
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CBSE Class 12 Biology past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.