CRISPR/CAS9 Flashcards
(16 cards)
What role does Cas9 play in the CRISPR/Cas9 system?
A) It repairs damaged DNA.
B) It cuts DNA at specific target sites.
C) It synthesizes RNA.
D) It acts as a guide to target DNA.
Cas9 is a DNA endonucleaseor protein or enzyme that makes precise cuts in the DNA at locations specified by the guide RNA.
What is the function of guide RNA (gRNA)?
A) To degrade viral DNA.
B) To direct Cas9 to the target DNA sequence.
C) To repair double-stranded breaks.
D) To bind to PAM sequences directly.
The guide RNA directs Cas9 to the target DNA sequence by complementary base pairing with the DNA, ensuring precision in editing.
What is a PAM sequence(5’-NGG-3’), and why is it important?
A) It protects the target DNA from being cut.
B) It is required for Cas9 to recognize and bind to the target DNA.
C) It encodes the guide RNA.
D) It triggers non-homologous end joining.
The PAM sequence (5’-NGG-3’) is essential for Cas9 to bind and cut DNA at the correct location. It is located immediately downstream of the target DNA.
Which of the following processes repairs double-strand breaks caused by CRISPR/Cas9?
A) Non-homologous end joining (NHEJ)
B) Homology-directed repair (HDR)
C) Both A and B
D) Neither A nor B
NHEJ is a quick repair mechanism but prone to errors, while HDR is more precise and uses a repair template to fix the break.
(C)
How does CRISPRa (CRISPR activation) function?
A) By cutting DNA at specific sites
B) By using dCas9 fused to activator proteins to enhance gene transcription
C) By fusing dCas9 with repressor proteins to block gene expression
D) By repairing DNA double-strand breaks
CRISPRa uses deactivated Cas9 (dCas9) fused to activator proteins to upregulate gene expression without cutting DNA.
What is the role of dCas9 in CRISPRi (CRISPR interference)?
A) It activates gene expression.
B) It repairs mutated genes.
C) It silences genes by blocking transcription.
D) It introduces single base changes.
In CRISPRi, dCas9 is fused with repressor proteins like KRAB to prevent transcription and silence the target gene.
What makes base editing different from standard CRISPR/Cas9 editing?
A) It targets RNA instead of DNA.
B) It changes single DNA bases without cutting both DNA strands.
C) It edits proteins directly.
D) It deletes entire genes
Base editing allows single-base changes (e.g., C to T or A to G) without introducing double-strand breaks in the DNA.
B
Which component is essential for prime editing?
A) A deactivated Cas9 (dCas9) protein
B) A prime editing guide RNA (pegRNA)
C) A reverse transcriptase enzyme
D) Both B and C
Prime editing relies on pegRNA to specify the edit and reverse transcriptase to synthesize the new DNA strand.
What is epigenome editing?
A) Changing DNA sequences permanently.
B) Modifying chemical tags on DNA or histones to regulate gene expression.
C) Replacing defective DNA with healthy DNA.
D) Silencing genes by cutting their promoter regions.
Epigenome editing uses modified CRISPR systems to alter histones or DNA modifications od chemical tags on DNA influencing gene expression without changing the DNA sequence.
What does CRISPR screening aim to do?
A) Identify essential genes for specific traits or functions.
B) Repair mutations in individual genes.
C) Modify RNA sequences.
D) Enhance protein synthesis
CRISPR screening helps discover genes responsible for traits or diseases by editing many genes and analyzing the resulting phenotypes.
What is the difference between in vivo and ex vivo CRISPR therapy?
A) In vivo is done inside the body, while ex vivo is done outside the body.
B) In vivo modifies RNA, and ex vivo modifies DNA.
C) In vivo edits germline cells, while ex vivo edits somatic cells.
D) There is no difference between them.
In vivo therapy involves editing directly inside the patient’s body, while ex vivo therapy modifies cells outside the body and reinserts them into the patient.
How is a guide RNA (gRNA) designed for Cas9?
A) By selecting a 20-base-pair sequence downstream of the PAM site.
B) By selecting a 20-base-pair sequence upstream of the PAM site.
C) By designing a sequence complementary to the PAM.
D) By inserting random sequences near the target DNA.
The guide RNA targets a 20-base-pair sequence upstream of the PAM to guide Cas9 to the correct DNA site.
What is a potential limitation of CRISPR/Cas9?
A) It only works in bacteria.
B) Off-target DNA cleavage can cause unintended mutations.
C) It cannot edit genes in human cells.
D) It cannot repair double-strand breaks.
Off-target effects occur when Cas9 cuts DNA at unintended sites, which could lead to harmful mutations or side effects.
What is the role of homology-directed repair (HDR) in CRISPR?
A) To fix double-strand breaks using a template for precise edits.
B) To quickly rejoin broken DNA ends without a template.
C) To prevent Cas9 from cutting DNA.
D) To insert random mutations in the DNA.
HDR uses a DNA template to accurately repair double-strand breaks, enabling precise editing, such as adding or replacing sequences.
What is the primary difference between somatic and germline gene editing?
A) Somatic editing modifies cells involved in reproduction, while germline editing modifies all other body cells.
B) Somatic editing affects the individual but is not passed to offspring, while germline editing affects future generations.
C) Germline editing is done outside the body, while somatic editing is done inside the body.
D) Germline editing only repairs damaged DNA, while somatic editing replaces genes entirely.
Somatic editing targets non-reproductive cells, affecting only the individual, and cannot be passed to offspring.
Germline editing targets reproductive cells (eggs, sperm) and can affect future generations by passing changes to descendants.
(B)
Compare and contrast base editing and prime editing
Similarities:
- both do not cut DNA
Differences:
- base editing :
cuts a single base and uses Casnickase/Cas fused to deaminase.
- prime editing does insertions, deletions, or replace specific dna sequences and uses cas9nickase fused to pegRNA
