Microbial Genetics: Lecture and Textbook Chapter 8

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Questions and Answers

A microbial geneticist is studying a newly discovered bacterium with a unique genome structure. They find that the bacterium contains a chromosome composed of DNA as well as several plasmids. If the bacterium suffers a mutation that inactivates DNA gyrase, what is the most likely consequence?

The bacterium's DNA will become overwound, inhibiting replication and transcription. (correct)
The bacterium will be unable to synthesize proteins.
The bacterium will exhibit increased antibiotic resistance due to plasmid integration into the chromosome.
The bacterium's chromosome will degrade due to increased susceptibility to exonucleases.

During a detailed analysis of the phosphodiester bonds in a bacterial DNA molecule, a research scientist discovers a novel modification where sulfur atoms replace some of the oxygen atoms in the phosphate backbone. Which of the following is the most likely consequence of this modification?

Increased susceptibility to hydrolysis by nucleases.
Enhanced binding affinity of histones, leading to chromatin condensation.
Increased rate of DNA replication due to improved polymerase processivity.
Altered DNA flexibility and interaction with DNA-binding proteins. (correct)

In a synthetic biology experiment, researchers engineer a bacterial strain to incorporate a modified nucleotide base that forms four hydrogen bonds with its complementary base, instead of the usual two or three. How would this modification most likely affect the DNA's properties and cellular processes?

Increased replication fidelity, but reduced accessibility for transcription factors.
Increased transcription rate due to easier strand separation.
Decreased melting temperature ($T_m$) and reduced stability of the DNA molecule.
Enhanced thermal stability and increased resistance to denaturation. (correct)

A research team is studying a bacterial species isolated from an extreme environment. They discover that its DNA polymerase has an unusual proofreading mechanism that corrects errors at a rate 100-fold higher than E. coli. What is the most likely evolutionary trade-off associated with this enhanced fidelity?

Slower replication rate and reduced adaptability to new environments. (B) Signup and view all the answers

A team of molecular biologists is investigating a novel bacterium discovered in a deep-sea vent. They observe that during DNA replication, the lagging strand synthesis frequently terminates prematurely, resulting in shorter Okazaki fragments than those observed in E. coli. Which of the following molecular defects could explain this observation?

Reduced processivity of DNA polymerase on the lagging strand template. (C) Signup and view all the answers

Consider a scenario where a bacterial cell is engineered to express an exogenous RNA molecule complementary to the 5' untranslated region (UTR) of a specific mRNA. This RNA molecule binds with high affinity but does not trigger degradation of the mRNA. What is the most likely outcome of this interaction?

Reduced translation of the target mRNA by blocking ribosome binding. (B) Signup and view all the answers

A research team discovers a novel bacterial species that utilizes a modified form of RNA polymerase which is resistant to rifampicin and functions with a higher processivity than E. coli. However, this polymerase lacks the sigma ((\sigma)) subunit. What is the most likely consequence for the bacterium?

Random initiation of transcription and reduced regulation of gene expression. (C) Signup and view all the answers

A scientist is studying a bacterial strain undergoing nutrient starvation and observes an increase in the production of small non-coding RNAs (sRNAs) that base-pair with specific mRNAs. These sRNAs do not cause mRNA degradation but alter protein expression. What is the most probable mechanism by which these sRNAs modulate protein expression?

Blocking ribosome binding sites or altering mRNA secondary structure. (B) Signup and view all the answers

During the translation of a mRNA molecule in a bacterial cell, a rare modified nucleoside is incorporated into the anticodon loop of a specific tRNA. This modification enhances the tRNA's ability to recognize and bind to its corresponding codon, but also significantly reduces its interaction with elongation factor Tu (EF-Tu). What is the most probable outcome of this situation?

Stalled ribosomes and reduced protein synthesis due to inefficient tRNA delivery. (A) Signup and view all the answers

A mutation occurs in a bacterial gene encoding a tRNA that recognizes the codon UAG (a stop codon) and inserts the amino acid glutamine instead of terminating translation. What is the most likely consequence of this mutation?

Synthesis of elongated proteins with C-terminal extensions beyond the normal stop codon. (D) Signup and view all the answers

A team of researchers is studying a bacterial strain that exhibits a significantly elevated mutation rate. They discover that the strain has a loss-of-function mutation in a gene encoding a protein with structural homology to eukaryotic RecQ helicases. What is the most likely role of the mutated bacterial protein?

Essential for resolving stalled replication forks and preventing DNA breaks. (D) Signup and view all the answers

Consider a bacterial cell exposed to a mutagen resulting in a specific base modification that causes the DNA polymerase to stall during replication. The cell's DNA repair mechanisms recognize the modified base, but instead of excising it, the repair system inserts a chemically similar, but non-native, base analog. What is the most likely outcome of this repair process?

Fixation of a novel mutation due to the incorporation of a non-natural base. (A) Signup and view all the answers

A bacterial strain has evolved a novel mechanism to resist a specific antibiotic. The resistance is due to a mutation that alters the ribosome structure, preventing the antibiotic from binding. However, this altered ribosome also reduces the efficiency of translation initiation for a subset of essential genes. Which of the following secondary mutations would most likely compensate for the fitness cost associated with the antibiotic resistance?

A mutation that increases the affinity of the altered ribosome for the Shine-Dalgarno sequence. (B) Signup and view all the answers

A bacterial cell integrates a new plasmid containing a gene that encodes a small RNA (sRNA) molecule that is antisense to a chromosomal mRNA transcript. This sRNA is also engineered to contain a sequence that recruits an RNase to degrade the targeted mRNA. What is the most likely outcome?

Selective degradation of the targeted chromosomal mRNA, leading to gene silencing. (B) Signup and view all the answers

A microbiologist is studying a bacterial species capable of undergoing natural transformation. The species contains a highly active restriction-modification system that efficiently degrades foreign DNA. What evolutionary advantage could explain the maintenance of natural competence in this species, despite the presence of an apparently counteractive DNA degradation system?

Natural transformation provides a mechanism for DNA repair, utilizing homologous sequences from the environment to correct chromosomal damage. (A) Signup and view all the answers

During a conjugation experiment, an E. coli F+ strain carrying a lacZ gene is mated with an F- strain lacking the lacZ gene. However, the F+ strain also carries an IS element near the lacZ gene on the F plasmid. Following conjugation, it is observed that the recipient strain not only acquires the lacZ gene, but also exhibits a chromosomal insertion of the IS element. What specific mechanism is most likely responsible for this observation?

Hfr conjugation, where the F plasmid integrates into the donor chromosome via the IS element, followed by transfer of chromosomal DNA to the recipient. (A) Signup and view all the answers

A research team is investigating a bacterial pathogen that exhibits unusually high rates of horizontal gene transfer (HGT). They discover that this species contains a novel class of integrative conjugative elements (ICEs) that can efficiently excise from the chromosome, transfer to new hosts, and integrate into diverse genomic locations. However, these ICEs lack a functional integrase gene. How do these ICEs most likely facilitate their integration into the host chromosome?

Hijacking host-encoded recombinases and utilizing short regions of homology for site-specific integration. (C) Signup and view all the answers

A bacterial geneticist is studying a temperate phage known to integrate into specific sites on the host chromosome. The phage also carries a bacterial virulence gene. During lysogeny, a mutation occurs within the phage integrase gene, abolishing its function. What is the most likely outcome of this mutation during subsequent lytic cycles?

The phage will continue to replicate lytically, but will lose the ability to integrate into the host chromosome, potentially curing the host of the virulence factor. (C) Signup and view all the answers

A researcher is investigating a bacterial population that exhibits an unusually high frequency of transduction. They discover that the causative phage has a mutation that eliminates its ability to discriminate between host DNA and phage DNA during packaging. However, the phage retains all other functions. What is the most likely consequence of this mutation.

The rate of generalized transduction will increase, while the phage's ability to perform productive infections will decrease. (A) Signup and view all the answers

A researcher is studying a bacterial species producing a restriction enzyme that recognizes a six-base-pair sequence not found in its own genome. The team discovers that the gene for this enzyme was recently acquired via horizontal gene transfer from a distantly related species. What is the most plausible explanation for how this bacterium avoids self-cleavage, given that the restriction site is absent from its chromosome?

The incoming DNA was mutated to prevent the restriction enzyme from acting on its DNA. (B) Signup and view all the answers

Flashcards

What is genetics?

The science of heredity, studying genes and how traits are passed down.

What is Molecular Biology?

The science that deals with the study of DNA and protein synthesis.