Practice Test 8

In a DNA double helix, one strand has the sequence 5′-A T G C C A-3′. A second strand is synthesized using complementary base pairing and antiparallel orientation. Which statement best describes the sequence and direction of the new strand?

A researcher compares two nucleic acid duplexes in the same salt concentration: Duplex 1 is 30 bp with 70% G≡C pairs; Duplex 2 is 30 bp with 30% G≡C pairs. Both have identical sugar-phosphate backbones and are heated at the same rate. G≡C base pairs form three hydrogen bonds, while A=T base pairs form two hydrogen bonds. Base stacking interactions also increase with higher G≡C content because of stronger pi-pi interactions among adjacent bases. No proteins are present. Which statement best describes the expected difference in strand separation behavior between the duplexes as temperature increases?