Final answer:
Uracil (U) is the nitrogen-containing base that is found in RNA instead of DNA, which contains adenine (A), thymine (T), cytosine (C), and guanine (G). Uracil is excluded from the so-called 'DNA base club' because it replaces thymine in RNA nucleotides.
Step-by-step explanation:
The nitrogen-containing base being referred to is uracil (U), which is found in RNA and not DNA, thereby excluded from the 'DNA base club' which consists of adenine (A), thymine (T), cytosine (C), and guanine (G).
Each nucleotide in DNA and RNA contains a nitrogenous base, which is an important component for the structure of nucleic acids. The nucleotides in DNA consist of four different nitrogenous bases: adenine (A), guanine (G) cytosine (C), and thymine (T). Adenine and guanine are classified as purines, which have a double-ring structure while cytosine, thymine, and uracil are pyrimidines, which have a single-ring structure. Thymine is unique to DNA, and uracil replaces thymine in RNA, making it the base that is not part of the DNA structure.
Uracil is not part of the DNA base club because it is only found in RNA, not in DNA. In RNA, uracil replaces thymine as one of the four possible nitrogenous bases. The other three bases, adenine, guanine, and cytosine, are present in both DNA and RNA.