What characteristic of RNA distinguishes it from DNA?

The characteristic of RNA that distinguishes it from DNA is its composition of different bases. RNA contains uracil instead of thymine, which is present in DNA. This substitution is significant because it impacts the stability and function of the nucleic acid. Additionally, RNA is single-stranded, which allows it to fold into complex three-dimensional shapes, enabling various functional roles in cellular processes such as protein synthesis and regulation.

The other options address features that do not distinguish RNA from DNA. For instance, the double helix structure is specific to DNA and is not a trait of RNA, which usually exists as a single strand. Furthermore, while DNA uses deoxyribose as its sugar, RNA contains ribose, which has one more oxygen atom than deoxyribose. Statements regarding RNA being always double-stranded also do not hold true, as most forms of RNA are single-stranded. Thus, the correct identification of RNA's different bases is crucial for understanding its unique properties and functions in cells.