AP Biology Questions on CRISPR-Cas9 Gene Editing

🧬 Quick Study Guide

• 🎯 CRISPR-Cas9 Basics: CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a gene-editing technology derived from a bacterial defense system. Cas9 is an enzyme that acts like molecular scissors.
• ✂️ Mechanism: A guide RNA (gRNA) directs the Cas9 enzyme to a specific DNA sequence in the genome. The Cas9 enzyme then cuts the DNA at that location.
• 🔧 DNA Repair Pathways: After the DNA is cut, cells use either Non-Homologous End Joining (NHEJ), which is error-prone and can disrupt a gene, or Homology-Directed Repair (HDR), which uses a template to precisely repair or insert a gene.
• 📝 Guide RNA (gRNA): The gRNA is a short RNA sequence complementary to the target DNA sequence. It guides the Cas9 protein to the correct location in the genome.
• 🔬 Applications: CRISPR-Cas9 is used in various applications, including gene knockout, gene editing, gene therapy, and disease modeling.
• 🌱 Ethical Considerations: The use of CRISPR-Cas9 raises ethical concerns about germline editing (modifying DNA that can be passed to future generations) and the potential for off-target effects.
• 🌡️ Key Enzymes: Cas9 is the most commonly used enzyme, but other Cas enzymes (e.g., Cas12a, Cas13) are also used for different applications.

🧪 Practice Quiz

1. Which of the following is the primary function of the Cas9 protein in CRISPR-Cas9 gene editing?
   1. A. To synthesize new DNA strands
   2. B. To guide RNA to the ribosome
   3. C. To cut DNA at a specific location
   4. D. To transport mRNA out of the nucleus
2. What is the role of the guide RNA (gRNA) in CRISPR-Cas9?
   1. A. To provide the Cas9 protein with energy
   2. B. To direct the Cas9 protein to a specific DNA sequence
   3. C. To repair the DNA after it is cut
   4. D. To prevent off-target effects
3. Which DNA repair pathway is most likely to result in a gene knockout due to insertions or deletions (indels)?
   1. A. Homology-Directed Repair (HDR)
   2. B. Non-Homologous End Joining (NHEJ)
   3. C. Base Excision Repair (BER)
   4. D. Mismatch Repair (MMR)
4. What is a major ethical concern associated with CRISPR-Cas9 gene editing?
   1. A. The high cost of the technology
   2. B. The potential for off-target effects
   3. C. The lack of scientific publications on the topic
   4. D. The limited availability of Cas9 proteins
5. In Homology-Directed Repair (HDR), what is required to achieve precise gene editing?
   1. A. A guide RNA with a random sequence
   2. B. A template DNA sequence with the desired edit
   3. C. An absence of DNA ligase
   4. D. A high concentration of Cas9 protein
6. Which of the following is NOT a common application of CRISPR-Cas9 technology?
   1. A. Gene knockout
   2. B. Gene therapy
   3. C. Protein synthesis
   4. D. Disease modeling
7. What type of molecule is Cas9?
   1. A. A carbohydrate
   2. B. A lipid
   3. C. A protein
   4. D. A nucleic acid