Question 1

Which of the following best describes the difference between transcription and translation in prokaryotic cells?

Accepted Answer

Transcription synthesizes mRNA from a DNA template in the cytoplasm, while translation synthesizes proteins from mRNA at ribosomes.

Question 2

A scientist is studying a gene that is always expressed at a constant level, regardless of environmental conditions. This gene is most likely:

Accepted Answer

A constitutively expressed gene, which provides a constant supply of its product.

Question 3

Which of the following statements correctly compares repressible and inducible operons?

Accepted Answer

A repressible operon is usually on and can be turned off by a co-repressor, while an inducible operon is usually off and can be turned on by an inducer.

Question 4

In the lac operon, what is the role of catabolite repression?

Accepted Answer

It prevents the use of lactose when glucose is available by inhibiting cAMP production, which is required for CAP activation of the lac operon.

Question 5

A base substitution mutation that changes a codon from $$	ext{UAC} ($$tyrosine) to $$	ext{UAA} ($$stop codon) is best described as:

Accepted Answer

A nonsense mutation

Question 6

Which of the following best explains the purpose of the Ames test?

Accepted Answer

To assess the mutagenic potential of chemical compounds using auxotrophic bacteria.

Question 7

Horizontal gene transfer in bacteria is significant because:

Accepted Answer

It enables bacteria to acquire new genetic traits, such as antibiotic resistance, from other organisms.

Question 8

Which of the following is NOT a type of horizontal gene transfer in bacteria?

Accepted Answer

Binary fission

Question 9

During bacterial conjugation, which type of cell contains the F plasmid integrated into its chromosome and can transfer chromosomal genes to a recipient?

Accepted Answer

Hfr cell

Question 10

A plasmid is best described as:

Accepted Answer

A small, circular DNA molecule that can replicate independently and can be transferred by conjugation, transformation, or transduction.

Question 11

What is an R factor, and why is it important in medical microbiology?

Accepted Answer

A plasmid carrying antibiotic resistance genes, contributing to the spread of antibiotic resistance among bacteria.

Question 12

Which of the following statements about transposons is correct?

Accepted Answer

Transposons are segments of DNA that can move from one location to another within a genome, facilitating horizontal gene transfer.

Question 13

According to Woese’s three-domain system, which of the following is NOT a domain?

Accepted Answer

Protista

Question 14

Which of the following is the correct way to write the full scientific name of a species?

Accepted Answer

Escherichia coli

Question 15

Which classification method relies on the analysis of ribosomal RNA sequences?

Accepted Answer

Molecular methods

Question 16

A clinical laboratory uses the MALDI-TOF technique to identify a bacterial isolate. What is the principle behind this method?

Accepted Answer

It measures the mass-to-charge ratio of proteins to generate a unique spectral fingerprint.

Question 17

Which of the following best differentiates a dichotomous key from a cladogram?

Accepted Answer

A dichotomous key is used for stepwise identification based on observable traits, while a cladogram illustrates evolutionary relationships.

Question 18

A patient is infected with a bacterial strain that has acquired resistance to multiple antibiotics. Which genetic element is most likely responsible for this trait, and how could it have been acquired?

Accepted Answer

An R factor plasmid acquired through horizontal gene transfer such as conjugation.

Question 19

A frameshift mutation is most likely to result from which of the following genetic changes?

Accepted Answer

The insertion or deletion of one or more nucleotides that is not a multiple of three.

Question 20

Which of the following best describes the use of auxotrophs in the Ames test?

Accepted Answer

Auxotrophs are used because they require a specific nutrient, and reversion to prototrophy indicates a mutation has occurred.

Microbial Genetics and Classification Study Guide

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