Question

Only RNA contains which of the following base-
A. Thymine
B. Uracil
C. Adenine
D. Cytosine

Answer 1

Hint: Nucleic acid comprises nitrogenous bases, DNA/RNA and a phosphate group. Nitrogenous bases are thymine (only in DNA), Cytosine, Adenine, Guanine and uracil.
DNA and RNA are considered to be the basis of the living world. Generally, DNA is considered to be stable and RNA are unstable.

Complete answer:
Nitrogenous bases pair up with the help of hydrogen bonds and phosphate sugar together to form nucleotides. Adenine, guanine and cytosine are found in both RNA and DNA, while thymine is found only in DNA, whereas uracil is found in RNA. Adenine is also a part of ATP that provides energy for chemical reactions in the cell. Cytosine as CTP also acts as a cofactor to enzymes. It is a compound found in living tissue as a constituent base of RNA. Uracil is the demethylated form of Thymine. It is an allosteric regulator and a coenzyme for reactions in plants and animals.
a) Thymine is present in DNA. It is one of the nitrogen bases found in DNA. It pairs up with adenine by two hydrogen bonds, i.e. A=T
b) Adenine: It is also present in both DNA and RNA. It pairs with thymine in DNA. It is one of the purines that helps in the stabilization of nucleic acid structures.
c) Cytosine: It is present in both DNA and RNA. It is a pyrimidine and pairs with guanine (purine) by a triple hydrogen bond.
So, option B is the correct answer.

Note: Nucleic acids are biopolymers and DNA and RNA are the basic structure of nucleic acid.
Cytosine and guanine nitrogenous bases are purines, while adenine and thymine are pyrimidines. Purines are six-membered nitrogen-containing rings attached to an imidazole ring, while pyrimidines are six-membered nitrogen-containing rings. A nucleic acid comprises nucleotide (nitrogen bases DNA/RNA) and a phosphate group.