AP Biology questions on gene regulation by non-coding RNAs

📚 Quick Study Guide

• 🧬 Non-coding RNAs (ncRNAs): These are RNA molecules that are transcribed from DNA but not translated into proteins. Instead, they have various regulatory functions.
• 🔬 MicroRNAs (miRNAs): Small ncRNAs (~22 nucleotides) that bind to mRNA, usually in the 3'UTR, to inhibit translation or promote mRNA degradation.
• 🎯 Mechanism of miRNA Action: miRNAs associate with the RISC (RNA-induced silencing complex). This complex then binds to target mRNA, leading to translational repression or mRNA cleavage.
• 🧪 Small Interfering RNAs (siRNAs): Similar to miRNAs, but usually derived from exogenous sources (e.g., viruses) or intentionally introduced. They lead to mRNA cleavage.
• ⚙️ Long Non-coding RNAs (lncRNAs): ncRNAs longer than 200 nucleotides with diverse functions, including scaffolding protein complexes, regulating transcription, and influencing chromatin structure.
• 💡 Regulation of Transcription: Some ncRNAs can recruit chromatin-modifying enzymes to specific genomic locations, altering gene expression.
• 📝 Examples of lncRNA function: Xist (X-inactive specific transcript) in X-chromosome inactivation.

🧪 Practice Quiz

1. Which of the following is the primary mechanism by which microRNAs (miRNAs) regulate gene expression?
   1. A. Enhancing mRNA translation
   2. B. Inhibiting mRNA translation or promoting its degradation
   3. C. Increasing DNA replication rate
   4. D. Promoting ribosome assembly
2. What is the typical size range of microRNAs (miRNAs)?
   1. A. 100-200 nucleotides
   2. B. 50-75 nucleotides
   3. C. Approximately 22 nucleotides
   4. D. Greater than 500 nucleotides
3. The RISC (RNA-induced silencing complex) is directly associated with the function of which type of non-coding RNA?
   1. A. Ribosomal RNA (rRNA)
   2. B. Transfer RNA (tRNA)
   3. C. MicroRNA (miRNA)
   4. D. Messenger RNA (mRNA)
4. Which of the following is a key difference between miRNAs and siRNAs?
   1. A. miRNAs are typically shorter than siRNAs
   2. B. siRNAs usually originate from exogenous sources, while miRNAs are endogenous
   3. C. miRNAs cleave mRNA, while siRNAs inhibit translation
   4. D. siRNAs function in the nucleus, while miRNAs function in the cytoplasm
5. Long non-coding RNAs (lncRNAs) are characterized by which feature?
   1. A. They are always translated into proteins
   2. B. They are shorter than 200 nucleotides
   3. C. They can scaffold protein complexes and regulate transcription
   4. D. They primarily function in DNA replication
6. Which of the following is a known function of some non-coding RNAs in gene regulation?
   1. A. Directly catalyzing DNA replication
   2. B. Recruiting chromatin-modifying enzymes to specific genomic locations
   3. C. Directly repairing damaged proteins
   4. D. Transporting mRNA out of the nucleus
7. Xist is an example of which type of non-coding RNA and what is its function?
   1. A. miRNA; promotes mRNA translation
   2. B. siRNA; cleaves viral RNA
   3. C. lncRNA; involved in X-chromosome inactivation
   4. D. tRNA; carries amino acids during translation