Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

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What does RNA have that DNA does not?

  1. Thymine

  2. Double helices

  3. Uracil

  4. Deoxyribose

The correct answer is: Uracil

RNA contains uracil, which is a nitrogenous base that plays a critical role in the structure and function of RNA molecules. In RNA, uracil replaces thymine, which is found in DNA. This difference is significant because it affects the base pairing during processes like transcription, where RNA is synthesized from a DNA template. Additionally, RNA typically exists as a single-stranded molecule, while DNA is double-stranded, forming a double helix structure. The sugar in RNA is ribose, whereas DNA contains deoxyribose, which further distinguishes these two essential nucleic acids. These differences in composition and structure are foundational to the distinct roles that RNA and DNA play in cellular processes.

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