Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA?

Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA?


a.5'-A-C-T-G-C-3' with 3'-T-C-A-C-C-5'


b.5'-purine-pyrimidine-purine-pyrimidi... with 3'-purine-pyrimidine-purine-pyrimidine-5...


c.5'-A-C-T-T-G-3' with 5'-C-A-A-G-T-3'


d.5'-A-G-C-C-T-3' with 5'-T-C-G-G-A-3'

Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA?
A is incorrect because the last c does not bond with the c in the second sequence.





B is incorrect because purines do not bind with other purines, nor does pyrimidines bind with pyrimidines.





D is incorrect because in a double helix, one strand will be 5' - 3', and the other strand will be 3' - 5' in the same direction.





The answer, therefore, is C. if you flip the second sequence so the 5' end of one sequence compliments the 3' end of the other sequence, you will see that the base pairs also compliment.
Reply:D