In DNA, which base is thymine replaced by in RNA?

In RNA, thymine is replaced by uracil. This is a fundamental difference between DNA and RNA. In DNA, thymine pairs with adenine, forming a stable double helix structure. However, during the process of transcription, when DNA is converted into RNA, uracil takes the place of thymine. This means that when RNA is synthesized from a DNA template, adenine in the DNA will pair with uracil in the RNA, rather than with thymine as it would in DNA. This substitution is significant for the structure and function of RNA, which includes messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), each of which plays crucial roles in the synthesis of proteins. Uracil's presence in RNA also affects the overall stability and flexibility of RNA molecules compared to DNA.