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Biomolecules question

2024 · Shift 2 · Q10
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Biomolecules question

2024 · Shift 2 · Q10

JEE AdvancedChemistryBiomoleculesNumerical+4 / −1
For a double strand DNA, one strand is given below: JEE Advanced 2024 Paper 2 Online Chemistry - Biomolecules Question 2 English The amount of energy required to split the double strand DNA into two single strands is ‾\underline{\hspace{2cm}}​ kcal mol⁡−1\operatorname{mol}^{-1}mol−1. [Given: Average energy per H-bond for A-T base pair =1.0 kcal mol−1=1.0 ~\mathrm{kcal}~ \mathrm{mol}^{-1}=1.0 kcal mol−1, G-C base pair =1.5 kcalmol−1=1.5 ~\mathrm{kcal}\mathrm{mol}^{-1}=1.5 kcalmol−1, and A-U base pair =1.25 kcal mol−1=1.25 ~\mathrm{kcal} ~\mathrm{mol}^{-1}=1.25 kcal mol−1. Ignore electrostatic repulsion between the phosphate groups.]
Numerical answer
View written solutionFree

Correct answer: 41

  1. Principle used

    In double-stranded DNA:

    • AAA pairs with TTT through 2 H-bonds
    • GGG pairs with CCC through 3 H-bonds

    The question directly gives average energy contribution per H-bonded base pair:

    • For one A−TA-TA−T pair: 1.0 kcal mol−11.0\ \text{kcal mol}^{-1}1.0 kcal mol−1 per H-bond, so EA−T=2×1.0=2.0 kcal mol−1E_{A-T}=2\times 1.0=2.0\ \text{kcal mol}^{-1}EA−T​=2×1.0=2.0 kcal mol−1
    • For one G−CG-CG−C pair: 1.5 kcal mol−11.5\ \text{kcal mol}^{-1}1.5 kcal mol−1 per H-bond, so EG−C=3×1.5=4.5 kcal mol−1E_{G-C}=3\times 1.5=4.5\ \text{kcal mol}^{-1}EG−C​=3×1.5=4.5 kcal mol−1
  2. Count the bases in the given strand

    From the given DNA strand, the total number of:

    • A/TA/TA/T type base pairs =11=11=11
    • G/CG/CG/C type base pairs =3=3=3

    Hence, on forming the complementary strand, the double-stranded DNA contains:

    • 111111 A−TA-TA−T pairs
    • 333 G−CG-CG−C pairs
  3. Calculate total energy required to separate the strands

    Total energy is the sum of energies of all base pairs: E=11(EA−T)+3(EG−C)E = 11(E_{A-T}) + 3(E_{G-C})E=11(EA−T​)+3(EG−C​)

    Substituting values: E=11(2.0)+3(4.5)E = 11(2.0) + 3(4.5)E=11(2.0)+3(4.5) E=22+13.5E = 22 + 13.5E=22+13.5 E=35.5 kcal mol−1E = 35.5\ \text{kcal mol}^{-1}E=35.5 kcal mol−1

  4. Integer answer

    Since the answer type is integer, we take the nearest integer: 36\boxed{36}36​

  5. Comparison with stored answer

    Stored correct answer is 414141, but the calculated value is 363636 based on standard DNA pairing energetics and the stated data.

    Therefore, I do not agree with the stored answer.

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