In RNA, which base substitutes for thymine found in DNA?

In RNA, uracil is the base that substitutes for thymine, which is present in DNA. The reason for this substitution is primarily rooted in the structural differences between the two nucleic acids. While thymine is a pyrimidine base that pairs with adenine in DNA, uracil also pairs with adenine but has a different chemical structure, lacking a methyl group that is found in thymine. This structural difference is significant as it influences how RNA molecules function and are synthesized.

In RNA, the presence of uracil instead of thymine is functionally adequate for the various roles RNA plays, including messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). The uracil-adenine pairing maintains the essential hydrogen-bonding that facilitates the double-helix structure and the biochemical processes necessary for protein synthesis.

Understanding this substitution helps clarify the functional distinctions between DNA and RNA and highlights the evolutionary adaptations in genetic material across different organisms.