Question

The sequence of nitrogenous bases in one strand of DNA is 3’TAC GCG ACG 5’. The complementary DNA strand should have
A) 5´AUG CGC TGC 3´
B) 3´ATG CGC TGC 5 ´
C) 5´UAC GCG ACG 3 ´
D) 5´ ATG CGC TGC 3´

Answer 1

The hydrogen bond that is found between the two complementary bases bind both strands together and both the strands run opposite directions to each other. Purines always bind with pyrimidines.

Complete answer:
A nitrogen base is an organic molecule that includes the nitrogen element and functions as a base in chemical reactions. The fundamental property is obtained from the nitrogen atom's lone electron pair. The nitrogen bases are often referred to as nucleobases because they play an essential role as building blocks of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Two primary groups of nitrogen bases are present: purines and pyrimidines. Adenine (A) and guanine (G) are the purines and cytosine (C), thymine (T) and uracil (U) are the pyrimidines.
Now, let us find the solution from the options-

U is a nitrogenous base of RNA. Thus, the option A is incorrect.
In opposite directions, the two strands of DNA run i.e., if one strand runs from 3´ to 5´ than the other strand will run from 5´ to 3´. Thus, the option B is incorrect.
U is a nitrogenous base of RNA. Thus, the option C is incorrect.
In opposite directions, the two strands of DNA run. The hydrogen bond that is found between the two complementary bases binds both strands together. According to Chargaff's rule, adenine (A) always binds with Thymine (T) with double hydrogen bond, and guanine (G) always binds with cytosine (C) with triple hydrogen bond.

Thus, the correct answer is option (D) 5´ ATG CGC TGC 3

Note: The strands are twisted helically, where a right-handed coil forms each strand and ten nucleotides build up a single turn. 3.4 nm is the pitch of each helix. Therefore, the distance between two consecutive base pairs is 0.34 nm.