[Campbell Biology P.430] Which of the following statements accurately describes the function... | Practice Question

Which of the following statements accurately describes the function or characteristics of long noncoding RNAs lncRNAs as discussed in the text?

  • A: LncRNAs typically range from 200 to hundreds of thousands of nucleotides in length and are primarily responsible for coding proteins.
  • B: The XIST lncRNA initiates X chromosome inactivation by binding to and coating the chromosome, leading to its condensation into heterochromatin.
  • C: All identified lncRNAs have well-established functions, with none still debated by researchers.
  • D: LncRNAs exclusively function in regulating gene expression by directly activating promoters without mediator proteins.

Explanation

The text explicitly states: 'One lncRNA, long known to be functional, is responsible for X chromosome inactivation... In this case, lncRNAs—transcripts of the XIST gene located on the chromosome to be inactivated—bind back to and coat that chromosome. This binding leads to condensation of the entire chromosome into heterochromatin.' Option B directly reflects this information. Option A is incorrect because lncRNAs are noncoding. Option C is incorrect as their functional significance is still debated. Option D is incorrect as lncRNAs can act as scaffolds, bringing various components together, suggesting a more complex mechanism than direct activation without mediators.