Q: A student is mapping bacterial genes using conjugation and finds the following order: Pro, His, Lys, Trp, Ile. If the time between Pro and His is 14 minutes, and between His and Lys is 10 minutes, what is the total time from Pro to Ile?

$$14 + 10 + 10 + 11 = 45$$ \text{ minutes}$

Question 1

Which enzyme was critical in proving that DNA is the 'transforming principle' in the classic Avery-MacLeod-McCarty experiment?

Accepted Answer

DNase

Question 2

In the context of bacterial conjugation, what is the primary function of the F plasmid?

Accepted Answer

It allows for the transfer of genetic material between bacteria via a pilus.

Question 3

Which of the following best describes generalized transduction?

Accepted Answer

Transfer of any gene from a donor to a recipient cell due to random packaging of host DNA by a phage.

Question 4

A filterable agent (FA) in Zinder and Lederberg's experiment was hypothesized to be a bacteriophage because:

Accepted Answer

It could pass through a .45 micron filter but not a .22 micron filter.

Question 5

Which of the following is a key feature of Gram-positive bacterial transformation?

Accepted Answer

DNA enters the recipient cell in single-stranded form.

Question 6

In specialized transduction, which genes are most likely to be transferred?

Accepted Answer

Genes that are closely linked to the phage integration site.

Question 7

Why is transduction considered a rare event in bacterial populations?

Accepted Answer

It depends on the accidental packaging of host DNA by a phage.

Question 8

Which of the following best explains why the human intestine is a 'caldron of HGT'?

Accepted Answer

It has high bacterial cell density and mixed-species biofilms, enabling frequent genetic exchange.

Question 9

A student is mapping bacterial genes using conjugation and finds the following order: Pro, His, Lys, Trp, Ile. If the time between Pro and His is 14 minutes, and between His and Lys is 10 minutes, what is the total time from Pro to Ile?

Accepted Answer

$$14 + 10 + 10 + 11 = 45$$ 	ext{ minutes}$

Question 10

Which experiment would best distinguish between transformation and transduction as the mechanism of genetic exchange in bacteria?

Accepted Answer

Using a filter that allows only viruses to pass but not cells, and observing if genetic exchange still occurs.

Question 11

During generalized transduction, what is the fate of the bacterial DNA that is mistakenly packaged into a phage particle?

Accepted Answer

It can recombine with the recipient's chromosome, introducing new genetic traits.

Question 12

Which of the following statements about the transformasome complex in Gram-positive bacteria is correct?

Accepted Answer

It is responsible for the active uptake of single-stranded DNA.

Question 13

If a bacterium acquires antibiotic resistance through horizontal gene transfer in the gut, which mechanism is LEAST likely to be involved?

Accepted Answer

Binary fission

Question 14

Which of the following best describes the difference between generalized and specialized transduction?

Accepted Answer

Generalized transduction can transfer any gene, while specialized transduction transfers only genes near the phage integration site.

Question 15

Which of the following is NOT a requirement for bacterial transformation to occur?

Accepted Answer

Direct cell-to-cell contact is required.

Question 16

A bacterium is exposed to a mixture of DNA fragments from a lysed cell. Which process allows it to incorporate a new gene for lactose utilization?

Accepted Answer

Transformation

Question 17

Which of the following best explains why antibiotic exposure in the gut may increase horizontal gene transfer?

Accepted Answer

Antibiotics induce stress responses that can increase DNA uptake and gene exchange.

Question 18

Which of the following is a direct consequence of the headful packaging mechanism in generalized transduction?

Accepted Answer

Host chromosomal DNA can be mistakenly packaged into phage heads.

Question 19

Which of the following is the best definition of the 'transforming principle' as discovered in the 1940s?

Accepted Answer

A nucleic acid (DNA) that can transfer genetic information between cells.

Microbial Genetics II: Mechanisms of Genetic Exchange in Bacteria

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