Practice Test Exam 2

Microbiology

In feedback inhibition of a biosynthetic pathway, the end product most commonly:

Binds an allosteric site on the first enzyme, changing its conformation so the substrate cannot bind

A researcher discovers a bacterial secretion apparatus that consists of a long needle-like structure extending from the bacterial surface and is evolutionarily related to the bacterial flagellum. Which secretion system is most likely being studied?

Type III secretion system

A researcher wants to determine whether a bacterial strain can acquire a new antibiotic-resistance gene from purified DNA added directly to the growth medium. Which experiment would be most appropriate?

Add purified DNA containing the resistance gene to the bacterial culture and test for resistant cells

A bacterial strain is unable to acquire DNA from its surroundings even though the DNA is present in large quantities. Which cellular property is most likely missing?

Competence

Two bacterial strains are mixed. The donor contains a plasmid carrying antibiotic resistance , while the recipient does not. After incubation, some recipient cells become resistant. When the researchers prevent physical contact between the two bacterial populations using a membrane that allows DNA and proteins to pass but prevents the cells from touching, resistance transfer does not occur. Which mechanism is most consistent with these observations?

Conjugation

A bacteriophage infects a bacterial cell and accidentally packages a fragment of bacterial chromosomal DNA into a newly formed phage particle. The particle then infects another bacterium and delivers that bacterial DNA. Which process has occurred?

Transduction

A bacterial population contains a prophage integrated at a specific location in its chromosome. During excision the prophage accidentally removes neighboring bacterial genes and carries them into a new bacterial cell during a subsequent infection. Which type of horizontal gene transfer is most consistent with this scenario?

Specialized transduction

A researcher identifies a bacterial secretion apparatus that is structurally related to the machinery used by bacteria to assemble and rotate their flagella. The apparatus allows the bacterium to deliver proteins directly into a eukaryotic host cell. Which secretion system is most likely involved?

Type III secretion system

A bacterial pathogen possesses a functional Type III secretion system but produces a mutant version of one of its secreted effector proteins. Which result would best demonstrate that the effector, rather than the secretion apparatus itself, is responsible for a particular virulence phenotype?

The mutant bacteria can still secrete proteins but no longer produce the specific host-cell alteration caused by that effector

A newly discovered bacterium possesses a secretion system that can transfer proteins between bacterial cells and is also capable of transferring DNA under certain circumstances. Which existing secretion system is most consistent with these observations?

Type IV secretion system

A researcher studies a bacterial community and observes that one species kills neighboring bacterial cells using a contact-dependent secretion apparatus. Which observation would most strongly support the hypothesis that a Type VI secretion system is responsible?

The bacteria inject toxic proteins into neighboring bacterial cells after making physical contact

A bacterium has a mutation that prevents CheA from autophosphorylating but all of the other chemotaxis proteins and the flagellar motor are functional. The bacterium is placed in a uniform environment with no attractant or repellent. Which phenotype would you most likely observe?

CheY remains unphosphorylated, causing the flagellum to rotate primarily counterclockwise and reducing tumbling

A researcher compares two bacterial populations growing under identical conditions. Population A has low intracellular c-di-GMP, whereas Population B has high intracellular c-di-GMP. Which observation would provide the strongest evidence that c-di-GMP is influencing the populations as expected?

Population B forms a stronger biofilm, produces more extracellular polysaccharide, and displays reduced motility

In a bacterial operon with 3 genes, if gene 1 is actively being expressed, what can you say about gene 3?

It is also being expressed

What is a common feature of DNA that is bound by proteins?

It has inverted repeats

Which molecule acts as a corepressor for the Tryptophan biosynthesis operon?

Tryptophan

Which component of a two-component system is present in the cell membrane and acts as a receptor protein?

Sensor Kinase

Which of the following is commonly a quorum sensing molecule?

Acyl homoserine lactones

Aliivibrio fischeri is used for which of the following?

Produces visible light in a light organ in an animal symbiosis

If given the choice between metabolizing lactose or glucose, bacteria will utilize which sugar first? |

Glucose

Like P. aeruginosa, P. fluorescens uses cyclic-di-GMP as an intracellular signaling molecule to determine whether or not to form a biofilm. However, P. fluorescens also senses __________ as an indicator of nutritional content which controls expression of surface proteins important for attachment.

Phosphate levels

DnaA binds to _______________ DNA more tightly than DnaA.

Methylated

What is the opposite of sporulation?

Germination

Which is a good target for an antibiotic?

Peptidoglycan, Bacterial ribosomes, Bacterial transcription, Bacterial translation

A Caulobacter mutant that cannot make crescentin would be expected to:

grow as straight rods rather than curved cells

In Caulobacter, which regulator, when phosphorylated in the swarmer cell, activates flagellar genes and blocks initiation of DNA replication by binding the origin?

CtrA

Why are cells growing in a biofilm often more resistant to antibiotics than planktonic cells of the same strain?

Multidrug efflux pump genes (e.g. AcrAB-TolC in E. coli) are upregulated, and matrix polysaccharides can limit antibiotic penetration

A mutation that introduces a different amino acid in the polypeptide that the gene encodes is a ___________ mutation.

Missense

Which of these indicates a bacterium that previously had an F plasmid integrated into the chromosome, but upon excision from the chromosome, took some chromosomal DNA with it?

F’

Which of these can be a recipient of an F plasmid?

F−

Which statement correctly distinguishes the Sec and Tat translocases?

Sec exports unfolded proteins, whereas Tat transports folded proteins, including those that carry cofactors

Which statement about an operon is correct?

Two or more genes are transcribed from one promoter, so they are regulated together

A regulatory protein is a homodimer. Why is this useful for binding an inverted repeat?

Each identical polypeptide has a DNA-binding domain that contacts one half of the inverted repeat

A mutant E. coli has a lacI mutation that prevents LacI from binding the operator. Cells are grown with neither glucose nor lactose. What do you expect for lac operon expression?

High expression, because no repressor blocks the operator and cAMP is high enough for CRP to activate transcription

A cheR mutant cannot methylate its MCPs. Which phenotype do you predict?

The cells stay strongly responsive to attractants and insensitive to repellents

Why might quorum-sensing disruptors be useful as drugs?

They could prevent virulence gene expression and help disperse biofilms

Small regulatory RNAs (sRNAs) can do all of the following EXCEPT:

Methylate promoter DNA to recruit RNA polymerase

How does an anti-sigma factor regulate gene expression?

It binds a sigma factor and inactivates it

A Bacillus mutant cannot phosphorylate Spo0A. What do you expect when the cells are starved?

The cells will not proceed to sporulation

In Caulobacter, after CtrA is degraded, which protein rises and triggers DNA replication?

DnaA

Which of the following is NOT one of the four classes of genetically encoded antibiotic resistance mechanisms?

Increased uptake of the antibiotic

In replica plating, colonies from a master plate containing histidine are transferred to a plate lacking histidine. Which colony is a His− auxotroph?

One that grows on the master plate but not on the replica plate

A recipient strain has a nonfunctional copy of a gene. A plasmid carrying a functional wild-type copy restores the wild-type phenotype. This restoration is called:

Complementation

Why can a generalized transducing particle not cause a lytic infection in the recipient cell?

It contains host bacterial DNA instead of a phage genome, so it is defective

An F+ donor is mixed with an F− recipient. After conjugation, which statement is true?

Both cells carry a complete F plasmid