Question

Which one is the correct base pairing for a DNA molecule?
A. Adenine – Thymine
B. Thymine – Guanine
C. Cytosine – Uracil
D. Thymine – Uracil

Answer 1

A base pair (bp) is the basic unit of a double-stranded nucleic acid made up of two nucleic bases linked together by hydrogen bonds. They make up the building blocks of the DNA double helix and contribute to the folded structure of DNA and RNA. Identified by specific hydrogen-bonding patterns, the "Watson-Crick" base pair allows the DNA helix to maintain a regular helix structure dependent on its nucleotide sequence.

Complete answer:
Option A: Adenine – Thymine: Adenine and thymine are two of the four chemical bases in DNA. The adenine bases in a DNA molecule which are located on one strand form chemical bonds with thymine bases on the opposite strand. The thymine, which is also known as -methyluracil, is a pyrimidine nucleobase.
Since adenine and thymine forms a base pair, option A is the correct answer.
Option B: Thymine – Guanine: Thymine is one of the four nucleic bases of nucleic acids. In the double helix, thymine pairs with adenine, or nucleotide A. In DNA, guanine pairs with cytosine. Guanine nucleosides are called guanosine.
Since thymine pairs with adenine, option B is not correct.
Option C: Cytosine – Uracil: The cytosine bases in DNA molecules which are located on one strand form chemical bonds with guanine bases on the opposite strand. Uracil binds to adenine in RNA molecules via two hydrogen bonds. In DNA, thymine replaces the uracil nucleobase.
Since cytosine pairs with guanine, option C is not correct.
Option D: Thymine – Uracil: Thymine bases located on one strand form chemical bonds with adenine bases on the opposite strand. The uracil binds to adenine by two hydrogen bonds in an RNA molecule. In DNA, thymine replaces the uracil nucleobase. Uracil is a demethylated form of thymine.
Since thymine does not pair with uracil, option D is not correct.

So, the correct answer is “Option A”.

Note:
The complementary nature of base pairing structure provides a backup copy of the genetic information encoded in each DNA strand. The regular structure and data redundancy provided by the DNA double helix make DNA suitable for storing genetic information, while the bae pairing between DNA and incoming nucleotides provides the mechanism by which DNA polymerase replicates DNA and RNA polymerase transcribes DNA into RNA.