Answer:
A, G, C, T, U are the nucleotide bases which are present in the DNA and RNA. In DNA, adenine (A), guanine (G), cytosine (C) and Thymine (T) are present. In RNA, adenine (A), guanine (G), cytosine (C) and Uracil (U) are present.
Adenine (A) and Guanine (G) are purines.
Cytosine (C), Thymine (T) and Uracil (U) are pyrimidines.
Adenine (A) pairs with Thymine (DNA) and Uracil (U) in case of RNA.
Cytosine pairs with guanine (G).