Question 1

Which of the following best explains why DNA polymerase cannot initiate DNA synthesis de novo during replication?

Accepted Answer

It requires a free 3'-OH group provided by an RNA primer to add nucleotides.

Question 2

A bacterial cell is exposed to both glucose and lactose. Which of the following best describes the expected transcriptional activity of the lac operon?

Accepted Answer

Transcription is minimal due to catabolite repression caused by low cAMP levels.

Question 3

A scientist isolates a mutant E. coli strain that cannot grow on minimal media lacking tryptophan. Which genetic mechanism most likely explains this phenotype?

Accepted Answer

A mutation in the trp operon structural genes prevents tryptophan biosynthesis.

Question 4

During the lytic cycle of a bacteriophage, which step immediately follows biosynthesis?

Accepted Answer

Maturation (assembly of viral components)

Question 5

A patient develops a secondary infection with Candida albicans after a course of broad-spectrum antibiotics. Which concept best explains this phenomenon?

Accepted Answer

Disruption of normal microbiota reduces microbial antagonism, allowing opportunistic pathogens to proliferate.

Question 6

Which of the following equations correctly represents the antiparallel orientation of DNA strands?

Accepted Answer

$$5' \rightarrow 3'$$ and $$3' \rightarrow 5'$$

Question 7

A researcher is studying a virus with a (-) ssRNA genome. Which enzyme must be present in the virion for successful infection of a host cell?

Accepted Answer

RNA-dependent RNA polymerase

Question 8

Which of the following best describes the process of transformation in bacteria?

Accepted Answer

Uptake of free, extracellular DNA fragments from the environment by competent cells.

Question 9

A patient is diagnosed with sepsis. Which of the following best defines this condition?

Accepted Answer

A systemic inflammatory response due to active multiplication of pathogens in the blood.

Question 10

Which of the following scenarios best illustrates the concept of herd immunity?

Accepted Answer

A high percentage of a population is vaccinated, reducing the spread of measles even among unvaccinated individuals.

Question 11

Which of the following is a key difference between prokaryotic and eukaryotic protein synthesis?

Accepted Answer

Prokaryotes use formylmethionine (fMet) as the initiator amino acid, while eukaryotes use methionine (Met).

Question 12

A viral genome is found to be composed of both DNA and RNA. Based on your knowledge, what is the most likely explanation?

Accepted Answer

This is not possible; viruses contain either DNA or RNA, never both.

Question 13

Which of the following best describes the function of DNA ligase during DNA replication?

Accepted Answer

It creates covalent phosphodiester bonds to join Okazaki fragments on the lagging strand.

Question 14

A patient presents with cold sores that recur periodically. Which type of viral infection does this represent?

Accepted Answer

Latent infection

Question 15

Which of the following best explains why selective toxicity is difficult to achieve with antiviral drugs?

Accepted Answer

Viruses rely on host cell metabolic machinery for replication.

Question 16

A researcher is using replica plating to identify auxotrophic mutants. Which of the following best describes this technique?

Accepted Answer

Transferring colonies from a master plate to minimal and enriched media to identify mutants unable to synthesize specific nutrients.

Question 17

Which of the following is the correct sequence of events for animal virus replication?

Accepted Answer

Attachment → Penetration → Uncoating → Biosynthesis → Maturation → Release

Question 18

Which of the following best describes the role of allosteric regulation in metabolic pathways?

Accepted Answer

The end-product binds to an allosteric site on an early enzyme, causing a conformational change that inhibits enzyme activity.

Question 19

A hospital patient acquires a new infection with a multidrug-resistant bacterium during their stay. This is best classified as:

Accepted Answer

A healthcare-associated infection (HAI)

Question 20

Which of the following best describes the function of transposase in bacterial cells?

Accepted Answer

It cuts and reseals DNA at insertion sequences, enabling transposon movement.

BIO 1570 Microbiology Exam 2 Study Guide: Microbial Genetics, Virology, and Epidemiology

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