Question 1

Which of the following best describes the function of the CRISPR-Cas9 system in bacteria?

Accepted Answer

It acts as a molecular memory bank, storing fragments of viral DNA to recognize and destroy future invaders.

Question 2

During the adaptation (spacer acquisition) phase of the CRISPR-Cas mechanism, what occurs?

Accepted Answer

A short piece of foreign DNA is inserted into the CRISPR array between repeat sequences.

Question 3

What is the role of the PAM (Protospacer Adjacent Motif) sequence in the CRISPR-Cas9 system?

Accepted Answer

It ensures that Cas9 only cuts foreign DNA and not the bacterial genome.

Question 4

A researcher wants to knock out a gene in a mouse using CRISPR-Cas9. Which DNA repair pathway is most likely to introduce small insertions or deletions at the target site?

Accepted Answer

Non-homologous end joining (NHEJ)

Question 5

Which of the following is NOT a component required for CRISPR-Cas9 genome editing in eukaryotic cells?

Accepted Answer

trp operon

Question 6

In the context of CRISPR-Cas9, what is the function of the guide RNA (gRNA)?

Accepted Answer

It directs Cas9 to the specific DNA sequence to be cut by base pairing with the target DNA.

Question 7

A scientist introduces a donor DNA template along with CRISPR-Cas9 into a cell. Which DNA repair pathway is being utilized to insert a new gene at the target site?

Accepted Answer

Homology-directed repair (HDR)

Question 8

Which of the following equations best represents the process of a double-strand break (DSB) induced by Cas9 at a specific genomic locus?

Accepted Answer

$$DNA_{target} + Cas9:gRNA \rightarrow DNA_{target}^{DSB}$$

Question 9

Which real-world application of CRISPR-Cas9 is most directly related to agricultural biotechnology?

Accepted Answer

Developing pest-resistant or drought-tolerant crops

Question 10

A bacterial cell has survived a phage infection and now contains a new spacer in its CRISPR array. What is the most likely consequence if the same phage infects the cell again?

Accepted Answer

The crRNA will guide Cas9 to recognize and cleave the phage DNA, providing immunity.

Question 11

Which step in the CRISPR-Cas mechanism involves the processing of a long precursor RNA into individual guide RNAs?

Accepted Answer

Expression (crRNA biogenesis)

Question 12

Why is the PAM sequence critical for the specificity of Cas9-mediated DNA cleavage?

Accepted Answer

Cas9 requires the PAM sequence to distinguish foreign DNA from self DNA, preventing autoimmunity.

Question 13

Which of the following best explains why CRISPR-Cas9 is considered a 'revolutionary' tool in modern biology?

Accepted Answer

It allows precise, targeted modifications of DNA sequences in living cells.

Question 14

A scientist wants to use CRISPR-Cas9 to correct a point mutation in a human gene. Which of the following must be provided to the cell to achieve precise correction?

Accepted Answer

A donor DNA template with the correct sequence

Question 15

Which of the following is a potential medical application of CRISPR-Cas9 technology?

Accepted Answer

Therapeutic management of AIDS by editing immune cells

Question 16

In a CRISPR-Cas9 experiment, a double-strand break is introduced at a specific locus. If the cell repairs the break using non-homologous end joining (NHEJ), what is the most likely outcome?

Accepted Answer

Small insertions or deletions (indels) that may disrupt gene function

Question 17

Which of the following best describes the structure of a mature crRNA in the CRISPR-Cas system?

Accepted Answer

It contains a piece of the repeat sequence and a spacer sequence matching viral DNA.

Question 18

A company wants to engineer bacteria to produce a pharmaceutical compound using CRISPR-Cas9. Which step is essential for ensuring the new gene is inserted at the correct location?

Accepted Answer

Providing a donor DNA template with homology arms for HDR

Question 19

Which of the following is a correct sequence of events in the CRISPR-Cas immune response to viral infection in bacteria?

Accepted Answer

Spacer acquisition → crRNA biogenesis → Target destruction

CRISPR and Genomic Editing: Mechanisms and Applications

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