Question

A purified DNA sample of leaf contains 20.0 mole of guanine. Calculate the approximate percentage of purine residues?

(a) 30%

(b) 40%

(c) 60%

(d) 20%

This question was posed to me in final exam.

This interesting question is from Nucleic Acids in section Biomolecules and Catalysis of Life Sciences

Answer 1

The correct answer is (a) 30%

To explain: According to chargaff’s rules, C=G= 20%; A=T

                                                            (A+G) + (T+C) =100%

                                                         (A+20) + (T+20) =100%

                                                         (A+20) + (A+20) = 100%

                                                                                  2A= 100-40%

                                                                                   A = 30%.