40. Which of the four DNA compositions would have the highest melting temperatur

Question

40. Which of the four DNA compositions would have the highest melting temperature (assume equal length)? A. 20% T B. 30% G C. 40% A D. 40% C 41. In the Watson-Crick model of DNA structure now called B-form DNA): A) a purine in one strand always hydrogen bonds with a purine in the other strand. B) A-T pairs share three hydrogen bonds. D) the 5' ends of both strands are at one end of the helix. E) the bases occupy the interior of the helix. 42. UV radiation may damage DNA through the formation of A. Pyrimidine dimers B. Strand breaks and ring openings C. Depurination D. Thymine deamination E. Phosphorylation 43. A nucleoside and a nucleotide differ by: A phosphate B. The base present. C. A deoxy group D. A carbohydrate E. Mg ions 44. In the Watson-Crick model of DNA structure: A. both strands run in the same direction, 3'- 5; they are parallel. B. phosphate groups project toward the middle of the helix, where they are protected from interaction with water. c. T can form three hydrogen bonds with either G or C in the opposite strand. D. the distance between the sugar backbone of the two strands is just large enough to accommodate either two purines or two pyrimidines. E. the distance between two adjacent bases in one strand is about 3.4 A

Explanation / Answer

Ans 40 D 40% C

Guanine and cytosine are bonded with 3 hydrogen bonds whereas adenine and thymine are bonded by 3 hydrogen bonds.

More amount of energy is required to break GC pair as compared to AT pair and hence the one with highest amounts of G and C in the structure has highest melting temperature.

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