Question

In DNA, Adenine pairs with:
A. Guanine
B. Thymine
C. Cytosine
D. Uracil

Answer 1

Hint: The Deoxyribonucleic Acid or what we commonly call it as the DNA is a double helical structure in which the two polynucleotide strands coil around each other. The DNA is made up of nitrogenous bases, phosphate groups and a pentose sugar. Hereditary information is passed on from one generation to another with the help of this DNA.

Complete answer:
To solve the question, we must be aware of the structure of DNA.
> DNA is a spirally coiled structure in eukaryotes and circular in prokaryotes.
> It consists of nitrogenous bases which are grouped into Purines and Pyrimidines. Purines are 9-membered structures. They have a double ring in their structure and a total of four nitrogen atoms. Adenine and Guanine are the two purines.
> Pyrimidines have 6-membered rings in their structure. They have single rings unlike the purines. Pyrimidines have two nitrogen atoms. Cytosine and Thymine are two pyrimidines.
> Purines always pair with pyrimidines and vice-versa. Adenine pairs with Thymine while Cytosine pairs with Guanine. These bases pair with each other with the help of hydrogen bonds. A famous scientist E Chargaff gave a rule called the Chargaff’s rule. According to this rule Adenine pairs with Thymine with the help of two hydrogen bonds while the Cytosine pairs with Guanine with the help of three hydrogen bonds.

Therefore the correct answer to the question is option 2 i.e Thymine.

Note: Here it must be noted that in RNA (Ribonucleic acid), the nitrogenous base Thymine is absent. It is replaced by another nitrogenous base called Uracil. Therefore in RNA the nitrogenous base Adenine pairs with the nitrogenous base Uracil.