Question 1

A patient is infected with a Gram-negative bacterium that is resistant to multiple antibiotics. Which feature of Gram-negative bacteria most directly contributes to this resistance?

Accepted Answer

The presence of an outer membrane that limits drug entry

Question 2

During an outbreak, a strain of E. coli acquires a plasmid carrying a toxin gene from another bacterium. What type of gene transfer is this, and what is the most likely mechanism?

Accepted Answer

Horizontal gene transfer via conjugation

Question 3

Which of the following best explains why bacteria can transcribe and translate genes simultaneously, but eukaryotes cannot?

Accepted Answer

Bacteria lack a nuclear envelope, so ribosomes can access mRNA as it is transcribed

Question 4

A mutation changes a codon from UAU (tyrosine) to UAA (stop codon). What type of mutation is this, and what is its likely effect on the protein?

Accepted Answer

Nonsense mutation; results in premature termination

Question 5

Which enzyme is required for the synthesis of cDNA from an RNA template, and in which laboratory technique is this enzyme essential?

Accepted Answer

Reverse transcriptase; essential for RT-PCR

Question 6

A researcher uses blue-white screening to identify recombinant bacteria. What does the appearance of white colonies indicate?

Accepted Answer

The bacteria contain a recombinant plasmid with the gene of interest inserted

Question 7

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

Accepted Answer

Generalized transduction transfers any bacterial gene; specialized transduction transfers only specific genes near the prophage site

Question 8

A patient is diagnosed with a persistent viral infection. Which of the following best characterizes this type of infection?

Accepted Answer

The virus remains in the host, producing low levels of virus over a long period

Question 9

Which of the following statements about prions is correct?

Accepted Answer

Prions are infectious proteins that cause disease by inducing misfolding of normal proteins

Question 10

A patient presents with a fungal infection. Which of the following features distinguishes fungi from bacteria?

Accepted Answer

Fungi have chitin in their cell walls and sterols in their membranes

Question 11

A protozoan parasite survives in the environment as a cyst and in the host as a trophozoite. What is the main advantage of the cyst form?

Accepted Answer

It enables survival in harsh environmental conditions

Question 12

Which of the following best explains why antibiotics are ineffective against viruses?

Accepted Answer

Viruses lack peptidoglycan and ribosomes, so antibiotic targets are absent

Question 13

A patient is infected with a retrovirus. Which enzyme is essential for the replication of this virus, and what is its function?

Accepted Answer

Reverse transcriptase; synthesizes DNA from an RNA template ($$RNA \rightarrow DNA)$$

Question 14

Which of the following is a key reason why horizontal gene transfer is a major concern in the spread of antibiotic resistance among bacteria?

Accepted Answer

It allows rapid sharing of resistance genes between unrelated bacteria

Question 15

A laboratory is using PCR to amplify a DNA fragment. Why must the DNA polymerase used in PCR be heat-stable?

Accepted Answer

Because PCR involves repeated heating to denature DNA, which would inactivate most enzymes

Question 16

Which of the following best distinguishes a viroid from a virus?

Accepted Answer

A viroid consists only of naked RNA without a protein coat

Question 17

A patient is diagnosed with Taenia solium infection. Which is the infective stage for humans, and what is the most common route of infection?

Accepted Answer

Larva; ingestion of undercooked pork

Question 18

Which of the following best describes the function of quorum sensing in bacteria?

Accepted Answer

It allows bacteria to coordinate gene expression based on population density

Question 19

A patient is infected with Plasmodium. Which host is definitive, and what does this mean for the parasite's life cycle?

Accepted Answer

Mosquito; sexual reproduction occurs in the mosquito

Question 20

Which of the following is a key reason why standard sterilization procedures often fail to inactivate prions?

Accepted Answer

Prions are resistant to heat and proteases due to their abnormal protein conformation

Microbiology Exam 2 Study Guide: Genetics, Microbial Agents, and Infectious Diseases

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