Q: Which of the following equations correctly represents the process of bacterial transformation efficiency ($$E$$), where $$N_{colonies} is $$the number of colonies formed, $$ng_{DNA} is $$the amount of DNA used (in nanograms), and $$V_{total} is $$the total volume of the transformation mixture, with $$V_{plated}$$ being the volume plated?

$$E = \frac{N_{colonies} \times V_{total}}{ng_{DNA} \times V_{plated}}$$

Question 1

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

Accepted Answer

It acts as a molecular memory and defense system by storing snippets of viral DNA and using them to recognize and destroy future invaders.

Question 2

A scientist wants to use CRISPR-Cas9 to correct a point mutation in a gene. Which of the following components must be provided to the cell to achieve precise correction via homology-directed repair (HDR)?

Accepted Answer

Cas9 enzyme, guide RNA, and a DNA repair template containing the correct sequence.

Question 3

Which of the following equations correctly represents the process of bacterial transformation efficiency ($$E$$), where $$N_{colonies} is $$the number of colonies formed, $$ng_{DNA} is $$the amount of DNA used (in nanograms), and $$V_{total} is $$the total volume of the transformation mixture, with $$V_{plated}$$ being the volume plated?

Accepted Answer

$$E = \frac{N_{colonies} 	imes V_{total}}{ng_{DNA} 	imes V_{plated}}$$

Question 4

A bacterium uses a restriction-modification (R-M) system to defend against phage infection. What is the primary role of methyltransferase enzymes in this system?

Accepted Answer

To add methyl groups to the host DNA, protecting it from cleavage by restriction enzymes.

Question 5

Which of the following is a plausible reason why phages evolve anti-CRISPR (Acr) proteins?

Accepted Answer

To inhibit the activity of Cas enzymes and evade bacterial adaptive immunity.

Question 6

During the process of scaling up recombinant protein production, why is it important to progress from a single colony on an agar plate to a large industrial fermenter in stages?

Accepted Answer

To ensure genetic stability, strain purity, and consistent product yield.

Question 7

Which of the following best explains why engineered bacteria are used to produce human insulin instead of extracting it from pigs or cows?

Accepted Answer

Bacterial production of human insulin reduces allergic reactions and allows for large-scale, consistent manufacturing.

Question 8

A researcher is using electroporation to transform bacteria. What is the main effect of the electric pulse applied during this process?

Accepted Answer

It creates temporary pores in the bacterial membrane, allowing DNA to enter the cell.

Question 9

Which of the following is a real-world application of engineered bacteria producing polyhydroxyalkanoates (PHAs)?

Accepted Answer

Manufacturing biodegradable plastics for packaging and medical materials.

Question 10

In the context of the Red Queen dynamic, what is the evolutionary consequence of the ongoing arms race between bacteria and phages?

Accepted Answer

It drives rapid evolution and increased biological diversity in both bacteria and phages.

Question 11

A scientist is designing a guide RNA for CRISPR-Cas9 gene editing. Which sequence must be present adjacent to the target DNA site for Cas9 to recognize and cut?

Accepted Answer

A protospacer adjacent motif (PAM), such as NGG.

Question 12

Which of the following best describes the process of 'knocking out' a gene using CRISPR-Cas9?

Accepted Answer

Introducing a double-strand break that is repaired with small insertions or deletions, disrupting the gene's function.

Question 13

Which of the following steps is NOT typically part of downstream processing in industrial microbiology?

Accepted Answer

Optimizing oxygen levels in the bioreactor.

Question 14

A phage has evolved to wrap its DNA in a protein shell after entering a bacterial cell. What is the primary advantage of this strategy?

Accepted Answer

It physically shields the viral genome from host restriction enzymes and CRISPR machinery.

Question 15

Which of the following is a key regulatory requirement for the production of recombinant medical products such as insulin?

Accepted Answer

Compliance with Good Manufacturing Practices (GMP) and strict FDA oversight.

Question 16

Which of the following best explains the principle behind affinity chromatography used in protein purification?

Accepted Answer

Proteins are separated based on their specific binding to a ligand attached to the chromatography matrix.

Question 17

A bacterial cell triggers abortive infection (Abi) upon phage attack. What is the likely outcome for the bacterial population?

Accepted Answer

The infected cell dies, but the spread of the phage to neighboring cells is prevented.

Question 18

Which of the following is a critical step in ensuring only recombinant bacteria are selected after transformation with a plasmid?

Accepted Answer

Plating cells on agar containing an antibiotic for which the plasmid confers resistance.

Question 19

Which of the following is a plausible reason why phages with high mutation rates can evade bacterial CRISPR immunity?

Accepted Answer

Frequent changes in phage DNA sequence prevent recognition by guide RNAs derived from previous infections.

lec 15:Molecular Complexity, Bacterial Defense, and Synthetic Biology: Microbial Arms Race and Biotechnology Applications

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