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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3bm208

A double-stranded DNA segment has 10 base pairs, of which 4 are A-T pairs and 6 are G-C pairs. Count two H bonds per A-T pair and three per G-C pair, and phosphodiester bonds only within each strand. Which statements are correct?

  1. AThe total number of phosphodiester bonds is 18.
  2. BThe total number of hydrogen bonds between the strands is 26.
  3. CThe segment contains 20 nucleotide units.
  4. DForming the two strands from 20 free nucleotides releases 20 water molecules.

Answer: A, B, C

Each strand of 10 nucleotides has 9 phosphodiester bonds, so 18 in total. H bonds = 4 x 2 + 6 x 3 = 26. There are 2 x 10 = 20 nucleotide units. Each phosphodiester bond formed releases one water, so 18 water molecules are released, not 20.
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