52. Which of the following pairs bonds can rotate within a peptide backbone and the torsion angle of the latter assigned as phi angle? (A) N-Cα and Cα-CO (B) Cα-CO and N-Cα (C) CO-N and N-Cα (D) N-Cα and CO-N

4. Which description is NOT correct? (A) A nucleic acid consists of four kinds of bases linked to a sugar–phosphate backbone. (B) A pair of nucleic acid strands with complementary sequences can form a double-helical structure. (C) DNA is a structurally rigid molecule that only exist in a specific helical form. (D) Double-stranded DNA can wrap around itself to form a supercoiled structure.

52. Which of the following pairs bonds can rotate within a peptide backbone and the torsion angle of the latter assigned as phi angle?
(A) N-Cα and Cα-CO
(B) Cα-CO and N-Cα
(C) CO-N and N-Cα
(D) N-Cα and CO-N

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