Which base is not present in RNA?

In RNA (ribonucleic acid), the genetic material primarily consists of four bases: adenine, uracil, cytosine, and guanine. One of the distinguishing characteristics of RNA is that it does not contain thymine. Instead, uracil replaces thymine in the structure of RNA.

Thymine is a base that is found in DNA (deoxyribonucleic acid) and plays an essential role in base pairing with adenine during DNA replication and transcription. In contrast, during the synthesis of RNA, adenine pairs with uracil rather than thymine. The absence of thymine in RNA is an important aspect of its biological function and structural differences when compared to DNA.

Understanding the presence and absence of certain bases in nucleic acids is critical in genetics and molecular biology, as it helps elucidate the differences between DNA and RNA in terms of their structure, function, and roles in the cell.