Final Answer:
Nitrogenous bases consisting of a single ring are called pyrimidines.
Step-by-step explanation:
Pyrimidines are one of the two types of nitrogenous bases found in nucleotides, the building blocks of DNA and RNA. These bases consist of a single six-membered ring structure. The three common pyrimidine bases in DNA are cytosine (C), thymine (T) in DNA (or uracil (U) in RNA), and adenine (A). Their molecular structure comprises carbon and nitrogen atoms arranged in a ring shape. This single-ring structure distinguishes pyrimidines from the other class of nitrogenous bases, purines, which have a double-ring structure.
The specific arrangement of atoms in pyrimidines results in their ability to pair with complementary bases in the DNA double helix. For instance, in DNA, cytosine always pairs with guanine through three hydrogen bonds, while thymine (or uracil in RNA) pairs with adenine through two hydrogen bonds. This base pairing is crucial during DNA replication and transcription, ensuring accurate transmission of genetic information.
Understanding the distinction between pyrimidines and purines is fundamental in comprehending the structural and functional aspects of DNA and RNA. The single-ring structure of pyrimidines contributes to the overall stability and specificity of base pairing, vital for the genetic code's integrity and fidelity during cellular processes.