Prokaryote Biology EXAM ONE

Spring 26', Dr. Lessner, UARK PRO. BIO

In bacterial glycerophospholipids, how does a cell typically compensate for an increase in environmental temperature to maintain membrane fluid balance?

A.

By switching from ester-linked to ether-linked lipids to prevent hydrolysis.

B.

By incorporating more cis-unsaturated fatty acids to increase rigidity.

C.

By decreasing the concentration of hopanoids at the cell poles.

D.

By increasing the proportion of saturated fatty acids in the bilayer.

D.

By increasing the proportion of saturated fatty acids in the bilayer.

That's right!

Saturated fatty acids allow for tighter packing and higher melting points, which prevents the membrane from becoming excessively leaky or fluid at elevated temperatures.

What is the primary mechanism by which Type IV pili facilitate 'twitching motility' in bacteria?

A.

A biased random walk regulated by the phosphorylation of basal body proteins.

B.

The secretion of a polysaccharide slime that reduces friction for gliding.

C.

The repetitive extension and ATP-dependent retraction of the protein filament.

D.

The rapid rotation of the pilus base powered by the Proton Motive Force (PMF).

C.

The repetitive extension and ATP-dependent retraction of the protein filament.

Right answer

Twitching motility relies on the pilus attaching to a surface and then retracting, effectively pulling the cell body forward across that surface.

Why is pseudomurein, found in certain archaeal cell walls, unaffected by the administration of penicillin?

A.

Archaeal cells lack the specific transpeptidase enzyme that penicillin mimics.

B.

It contains β 1,3-glycosidic bonds instead of β 1,4-glycosidic bonds.

C.

Archaea utilize ether-linked sugars that penicillin cannot cleave.

D.

The thick S-layer prevents penicillin from reaching the underlying pseudomurein layer.

A.

Archaeal cells lack the specific transpeptidase enzyme that penicillin mimics.

Right answer

Penicillin functions by acting as a structural analog to the D-Ala-D-Ala peptide found in bacterial peptidoglycan, which is absent in pseudomurein.k

Which component is uniquely responsible for anchoring the peptidoglycan layer to the cytoplasmic membrane in Gram-positive bacteria while providing a net negative charge to the cell surface?

A.

Braun Lipoprotein

B.

Lipopolysaccharide (LPS)

C.

Meso-diaminopimelic acid (m-DAP)

D.

Teichoic acids

D.

Teichoic acids

That's right!

Teichoic acids and lipoteichoic acids extend through the peptidoglycan, anchoring it to the membrane and contributing significantly to the cell's surface charge.

In the Gram-negative cell envelope, what is the specific function of the Braun Lipoprotein?

A.

It covalently links the outer membrane to the underlying peptidoglycan layer.

B.

It is the primary endotoxin responsible for triggering Toxic Shock Syndrome.

C.

It acts as a sensor to trigger the PMF-driven flagellar motor.

D.

It functions as a non-specific porin for the transport of small cations.

A.

It covalently links the outer membrane to the underlying peptidoglycan layer.

That's right!

This abundant protein provides structural integrity by anchoring the outer membrane to the murein sacculus, maintaining the periplasmic space.

Lipid A, a crucial component of the lipopolysaccharide (LPS) layer, is medically significant because it acts as:

A.

The site where O-antigen attaches to the peptidoglycan.

B.

A selective porin that prevents the entry of large antibiotic molecules.

C.

An endotoxin that can cause a severe systemic immune response.

D.

An enzyme that degrades penicillin-like antibiotics.

C.

An endotoxin that can cause a severe systemic immune response.

Right answer

When Gram-negative bacteria die and lyse, the release of Lipid A into the bloodstream can trigger inflammation, fever, and shock.

Bacteria and Archaea can both possess fimbriae and pili. What is a key functional difference between a typical fimbria and a sex pilus?

A.

Fimbriae are used for genetic exchange, while pili are used solely for attachment.

B.

Only fimbriae are genetically encoded, while pili are acquired from the environment.

C.

Fimbriae facilitate surface adherence, whereas sex pili mediate horizontal gene transfer.

D.

Sex pili are powered by the PMF, while fimbriae are powered by ATP.

C.

Fimbriae facilitate surface adherence, whereas sex pili mediate horizontal gene transfer.

Right answer

Fimbriae allow bacteria to stick to tissues or surfaces, while sex pili facilitate conjugation between donor and recipient cells.

How does a flagellated bacterium achieve a 'biased random walk' toward an attractant concentration gradient?

A.

By physically steering the flagellar hook toward the chemical source.

B.

By lengthening the duration of 'runs' when moving up the concentration gradient.

C.

By utilizing magnetosomes to align with the chemical field of the nutrient.

D.

By increasing the frequency of 'tumbles' as it moves toward higher concentrations.

B.

By lengthening the duration of 'runs' when moving up the concentration gradient.

That's right!

When sensing an increase in an attractant, the cell suppresses the signal to change direction, allowing it to move longer in the favorable direction.

What is the primary role of porins in the Gram-negative outer membrane?

A.

To bind specifically to iron-containing magnetites in the environment.

B.

To generate the Proton Motive Force (PMF) for ATP synthesis.

C.

To allow for the passive diffusion of low-molecular-weight hydrophilic compounds.

D.

To actively pump antibiotics out of the periplasmic space.

C.

To allow for the passive diffusion of low-molecular-weight hydrophilic compounds.

That's right!

Porins act as channels that permit the passage of nutrients and small molecules through the otherwise impermeable lipid bilayer of the outer membrane.

The antibiotic Vancomycin inhibits cell wall synthesis by which mechanism?

A.

Inhibiting the synthesis of the core oligosaccharide in the periplasm.

B.

Cleaving the β 1,4-glycosidic bonds between NAG and NAM.

C.

Binding to the transpeptidase enzyme to block its active site.

D.

Binding directly to the D-Ala-D-Ala terminus of the pentapeptide.

D.

Binding directly to the D-Ala-D-Ala terminus of the pentapeptide.

Right answer

By capping the D-Ala-D-Ala tail, Vancomycin sterically hinders the transpeptidase enzyme from accessing its substrate, preventing cross-bridge formation.

Which of the following is a characteristic feature of archaeal membrane lipids that distinguishes them from bacterial and eukaryotic lipids?

A.

The use of fatty acids linked to glycerol via ester bonds.

B.

A bilayer structure that is always required for membrane integrity.

C.

The presence of branched isoprene-derived chains instead of straight-chain fatty acids.

D.

The incorporation of hopanoids to regulate membrane fluidity.

C.

The presence of branched isoprene-derived chains instead of straight-chain fatty acids.

That's right!

Archaeal lipids are synthesized from isoprene units (terpenes), leading to branched hydrophobic tails that contribute to membrane stability.

What serves as the energy source for the rotation of the bacterial flagellar motor?

A.

Phosphorylation of the FliG protein by GTP.

B.

The degradation of storage granules like poly-β-hydroxybutyrate.

C.

The flow of protons through the basal body driven by the PMF.

D.

Direct hydrolysis of ATP at the basal body.

C.

The flow of protons through the basal body driven by the PMF.

That's right!

The Proton Motive Force (PMF) provides the electrochemical energy required to turn the rotary motor embedded in the cell envelope.

During the Gram stain procedure, why do Gram-negative cells appear pink/red after the final step?

A.

The O-antigen on the LPS has a natural affinity for basic dyes like safranin.

B.

Their thick peptidoglycan layer traps the safranin counterstain permanently.

C.

Teichoic acids in the membrane react with safranin to produce a red color.

D.

The alcohol wash removes the crystal violet-iodine complex from their thin cell walls.

D.

The alcohol wash removes the crystal violet-iodine complex from their thin cell walls.

Right answer

The thin peptidoglycan and outer membrane of Gram-negative cells do not retain the primary stain during decolorization, allowing them to take up the counterstain.

Magnetosomes are specialized bacterial structures that allow cells to:

A.

Fix atmospheric nitrogen into ammonia for protein synthesis.

B.

Protect their DNA from ionizing radiation in deep-sea vents.

C.

Store iron for use as an alternative energy source during starvation.

D.

Orient themselves along Earth's magnetic field to find low-oxygen environments.

D.

Orient themselves along Earth's magnetic field to find low-oxygen environments.

That's right!

Magnetotactic bacteria are typically anaerobes that use internal magnetite crystals to swim downward toward sediment where oxygen levels are lower.

Which of Koch’s Postulates requires the researcher to grow the suspected pathogen in a 'pure culture'?

A.

Postulate 3: The same disease must occur when introduced to a healthy host.

B.

Postulate 1: The microbe is found in all cases of disease.

C.

Postulate 2: The microbe is isolated from the diseased host and grown.

D.

Postulate 4: The microbe must be re-isolated from the newly diseased host.

C.

Postulate 2: The microbe is isolated from the diseased host and grown.

That's right!

This step ensures that the specific organism can be studied independently of other microbes found in the host.

Carl Woese redefined the Tree of Life into three domains based on the sequence comparison of which molecule?

A.

Cytochrome c oxidase

B.

Peptidoglycan precursors

C.

16S ribosomal RNA (rRNA)

D.

Messenger RNA (mRNA)

C.

16S ribosomal RNA (rRNA)

That's right!

This molecule is found in all living organisms, is functionally constant, and evolves slowly, making it an ideal 'molecular chronometer'.

Why is Horizontal Gene Transfer (HGT) significant when constructing phylogenetic trees using genes like Glutamine Synthetase (GS)?

A.

It ensures that the GS tree perfectly matches the rRNA tree.

B.

It eliminates the need for PCR in genome sequencing.

C.

It can make distantly related organisms appear closely related.

D.

It prevents the acquisition of antibiotic resistance genes.

C.

It can make distantly related organisms appear closely related.

That's right!

If a gene is transferred between domains (e.g., from Bacteria to Plants), the phylogeny of that gene will reflect the transfer event rather than vertical ancestry.

What is the primary evolutionary advantage for a prokaryote to maintain a small cell size (e.g., high S/V ratio)?

A.

It maximizes the rate of nutrient uptake and waste diffusion.

B.

It protects the nucleoid from viral DNA injection.

C.

It allows for the storage of more complex organelles like mitochondria.

D.

It facilitates the formation of multicellular biofilms.

A.

It maximizes the rate of nutrient uptake and waste diffusion.

That's right!

A higher surface-area-to-volume ratio allows the cell to support its internal metabolic needs more efficiently through its outer membrane.

Which cytoskeletal-like protein is responsible for determining the rod-like shape of bacteria such as E. coli?

A.

Braun Lipoprotein

B.

MreB

C.

Crescentin (CreS)

D.

Tubulin

B.

MreB

That's right!

This actin analog forms a coil-like structure inside the cell to maintain the cylindrical 'rod' shape; its deletion leads to spherical cells.

What happens to the S-layer of a bacterium when it is repeatedly subcultured in a rich laboratory medium over many generations?

A.

The S-layer proteins begin to fix nitrogen for the cell.

B.

The bacteria may stop producing it to conserve energy.

C.

It transforms into a glycocalyx to improve surface attachment.

D.

It becomes thicker to protect against the high nutrient concentration.

B.

The bacteria may stop producing it to conserve energy.

That's right!

In a stable, 'perfect' environment without selective pressure (like predators or immune systems), cells favor energy conservation over-producing expensive protective layers.

In the context of the Endosymbiosis Theory, why are mitochondria and chloroplasts considered to have bacterial origins?

A.

They contain ether-linked lipids in their membranes.

B.

They possess their own circular genomes and 16S rRNA.

C.

They use methanogenesis to produce energy for the host cell.

D.

They are sensitive to the same viruses that infect modern Archaea.

B.

They possess their own circular genomes and 16S rRNA.

Right answer

The presence of bacterial-like DNA and ribosomes within these organelles provides strong evidence that they were once free-living prokaryotes.

Which enzyme is responsible for the 'transpeptidation' reaction during cell wall synthesis, and what is its substrate?

A.

Lysozyme; it acts on β 1,4-glycosidic bonds.

B.

eta-lactamase; it acts on the penicillin molecule.

C.

RNA polymerase; it acts on the NAG-NAM sugar backbone.

D.

Transpeptidase; it acts on the D-Ala-D-Ala terminus of the peptide side chain.

D.

Transpeptidase; it acts on the D-Ala-D-Ala terminus of the peptide side chain.

That's right!

This enzyme catalyzes the cross-linking of peptide chains, providing the cell wall with its essential structural rigidity.

How do methanogens, a group of Archaea, impact the Earth's climate?

A.

They degrade hopanoids in sedimentary rock, releasing trapped carbon.

B.

They produce methane (CH4​), a greenhouse gas that warmed the early Earth.

C.

They consume CO2​ and release O2​, cooling the planet.

D.

They form the ozone layer through the fixation of atmospheric nitrogen.

B.

They produce methane (CH4​), a greenhouse gas that warmed the early Earth.

That's right!

Pre-dating the rise of oxygen, methanogens released methane which helped trap heat, preventing the early Earth from freezing.

The bacterial nucleoid differs from a eukaryotic nucleus primarily because:

A.

It is located within a specialized protein compartment called a carboxysome.

B.

It contains linear chromosomes instead of circular ones.

C.

It lacks a surrounding membrane and is in direct contact with the cytoplasm.

D.

It uses RNA as the primary genetic material instead of DNA.

C.

It lacks a surrounding membrane and is in direct contact with the cytoplasm.

That's right!

Prokaryotic DNA is organized in a localized region of the cytoplasm without a membrane barrier, allowing for coupled transcription and translation.

Why is the use of 16SrRNA sequencing referred to as 'metagenomics' in the context of the Human Microbiome Project?

A.

It allows for the study of the entire genetic content of a microbial community without isolation.

B.

It allows researchers to create new species of Archaea in the lab.

C.

It is used to identify the specific magnets produced by E. coli.

D.

It specifically targets the genes responsible for insulin production in pathogens.

A.

It allows for the study of the entire genetic content of a microbial community without isolation.

That's right!

Metagenomics bypasses the need for pure cultures (which are often difficult to grow), providing a profile of all organisms present in a sample like the human gut.

Which of the following is the most accurate estimate of the number of prokaryotic cells currently existing on Earth, as cited in the source material?

A.

10^9

B.

10^31

C.

10^18

D.

10^21

B.

10^31

That's right!

Microbiologists estimate this massive quantity of prokaryotic cells, vastly outnumbering sand grains and human intestinal cells.

According to the geological evidence provided, approximately when did cellular life first originate, and when did eukaryotes emerge?

A.

Cellular life: 3.5 Gyr; Eukaryotes: 1 Gyr

B.

Cellular life: 4.5 Gyr; Eukaryotes: 2 Gyr

C.

Cellular life: 3.5 Gyr; Eukaryotes: 3.5 Gyr

D.

Cellular life: 2.5 Gyr; Eukaryotes: 0.5 Gyr

A.

Cellular life: 3.5 Gyr; Eukaryotes: 1 Gyr

That's right!

The source identifies the origin of cellular life around 3.5 billion years ago, with eukaryotes following significantly later at 1 billion years ago.

During the early Earth's climate development, which group of Archaea was responsible for warming the planet by producing CH4​ prior to the Great Oxidation Event?

A.

Cyanobacteria

B.

Hyperthermophiles

C.

Proteobacteria

D.

Methanogens

D.

Methanogens

That's right!

These Archaea produced methane gas, a potent greenhouse gas that helped maintain Earth's early temperature.

Which specific morphological term describes prokaryotes that appear as bent rods?

A.

Vibrios

B.

Cocci

C.

Bacilli

D.

Spirochetes

A.

Vibrios

Right answer

The term vibrio is used specifically to categorize bacteria with a curved or bent-rod morphology.

In the context of microbial metabolism, why is the Surface-to-Volume (S/V) ratio critical for small prokaryotic cells?

A.

Smaller cells have a lower S/V ratio, allowing them to store more nutrients.

B.

A high S/V ratio supports faster metabolic and growth rates due to efficient nutrient transport.

C.

A low S/V ratio is preferred by big cells to decrease the energy required for maintenance.

D.

The S/V ratio is irrelevant to growth rates as long as the cell has flagella.

B.

A high S/V ratio supports faster metabolic and growth rates due to efficient nutrient transport.

Right answer

A large surface area relative to a small volume ensures that nutrients can enter and waste can exit the cell rapidly enough to support high metabolic activity.

Carboxysomes are bacterial microcompartments that facilitate the concentration of which two essential components for autotrophy?

A.

Methane and methanogens.

B.

Sulfur and hydrolytic enzymes.

C.

Oxygen and ATP synthase.

D.

CO2​ and the enzyme RuBisCO.

D.

CO2​ and the enzyme RuBisCO.

That's right!

The protein shell of the carboxysome concentrates CO2​ near RuBisCO to increase the efficiency of the Calvin Cycle and prevent CO2​ loss.

What is the biological significance of gas vesicles in aquatic cyanobacteria?

A.

They prevent the cell from bursting under high osmotic pressure.

B.

They provide a reservoir of oxygen for aerobic respiration at night.

C.

They act as 'scaffolds' for the assembly of the flagellar motor.

D.

They provide buoyancy, allowing the cell to remain in the photic zone.

D.

They provide buoyancy, allowing the cell to remain in the photic zone.

That's right!

By regulating their density with gas-filled protein spindles, these bacteria can maintain their vertical position in the water column to maximize light absorption.

The 'Great Oxidation Event' approximately 2.4 billion years ago was primarily driven by which group of microorganisms?

A.

Hyperthermophiles

B.

Methanogens (Archaea)

C.

Cyanobacteria

D.

Proteobacteria

C.

Cyanobacteria

Right answer

Cyanobacteria evolved oxygenic photosynthesis, using water as a substrate and releasing O2​ as a byproduct, fundamentally changing Earth's atmosphere.

Which component of the Gram-negative cell envelope is known as an 'endotoxin' and can trigger toxic shock syndrome in humans?

A.

Porins

B.

Lipid A

C.

Braun lipoprotein

D.

Teichoic acid

B.

Lipid A

That's right!

Lipid A is the anchor of the lipopolysaccharide (LPS) in the outer membrane and acts as a powerful toxin when released.

If a bacterium like E.coli is moved from a cool environment to a high-temperature incubation (>50∘C), how will its membrane lipid composition likely change to maintain stability?

A.

Increase the proportion of saturated fatty acids.

B.

Convert all lipids into a monolayer.

C.

Decrease the amount of hopanoids present.

D.

Increase the proportion of unsaturated fatty acids.

A.

Increase the proportion of saturated fatty acids.

That's right!

Saturated fats pack more tightly, increasing rigidity and preventing the membrane from becoming too fluid or leaky in the heat.

Vancomycin resistance can occur in some Gram-positive bacteria through the modification of the peptidoglycan precursor. What is the typical substitution made?

A.

Substitution of L-Alanine for D-Alanine.

B.

Substitution of D-Ala-D-Ala with D-Ala-lactate.

C.

Substitution of m−DAP with Lysine.

D.

Substitution of NAM with NAG.

B.

Substitution of D-Ala-D-Ala with D-Ala-lactate.

That's right!

By changing the terminal sequence to a depsipeptide like D-Ala-lactate, the bacteria prevent Vancomycin from binding and inhibiting cell wall synthesis.

What happens to specialized surface layers, such as the Glycocalyx or S-layer, when pure cultures are grown continuously in optimal laboratory conditions?

A.

They transition from an S-layer to a thick capsule for better motility.

B.

They undergo horizontal gene transfer to share the trait with other lab strains.

C.

They become thicker to protect against the abundance of nutrients.

D.

The bacteria stop producing them because they are energetically unfavorable in the absence of selective pressure.

D.

The bacteria stop producing them because they are energetically unfavorable in the absence of selective pressure.

That's right!

Microbes are energy conservers; if protection or attachment isn't needed (as in a lab), the trait is often lost.

Why is the Glutamine Synthetase (GS) phylogenetic tree considered a contradiction to the universal tree of life based on 16S rRNA?

A.

Because GS is only found in Eukarya, making the comparison impossible.

B.

High levels of Horizontal Gene Transfer (HGT) and ancient gene duplications obscure the true vertical phylogeny.

C.

Because rRNA evolves much faster than the GS gene.

D.

Because the GS tree only accounts for psychrophiles.

B.

High levels of Horizontal Gene Transfer (HGT) and ancient gene duplications obscure the true vertical phylogeny.

That's right!

Lateral transfer of GS genes between distantly related species makes them appear more closely related than they are on an rRNA basis.

Which bacterial cytoskeletal protein is responsible for forming a coil inside rod-shaped cells to maintain their morphology?

A.

MreB

B.

FtsZ

C.

Flagellin

D.

CreS (Crescentin)

A.

MreB

Right answer

MreB is an actin analog that forms a helical coil to define and maintain the rod (bacillus) shape.

In the mechanism of bacterial chemotaxis, how does an organism 'bias' its movement toward an attractant?

A.

By increasing the frequency of counterclockwise (CCW) rotation as the concentration of the attractant increases.

B.

By only rotating the flagella in a clockwise (CW) direction when a repellent is present.

C.

By pointing its poles directly at the highest concentration of amino acids.

D.

By stopping all rotation and drifting with the current.

A.

By increasing the frequency of counterclockwise (CCW) rotation as the concentration of the attractant increases.

That's right!

CCW rotation results in 'runs' (straight swimming); increasing the duration of these runs based on a gradient directs the cell toward the source.

Which internal bacterial structure contains the enzyme RuBisCO and serves to concentrate CO2​ for fixation?

A.

Gas Vesicles

B.

Magnetosomes

C.

Thylakoids

D.

Carboxysomes

D.

Carboxysomes

That's right!

These protein-enclosed microcompartments house RuBisCO to facilitate the Kelvin cycle and prevent CO2​ loss.

What is the primary function of Magnetosomes in motile anaerobic bacteria?

A.

To store excess iron (Fe2+) for metabolic energy.

B.

To facilitate the transfer of DNA during conjugation.

C.

To generate a magnetic field that repels competing microbes.

D.

To orient the cell to Earth's magnetic field, allowing it to swim toward low-oxygen environments at the bottom of water columns.

D.

To orient the cell to Earth's magnetic field, allowing it to swim toward low-oxygen environments at the bottom of water columns.

That's right!

Magnetosomes act as internal compasses that guide anaerobes away from oxygen-rich surface waters.

Poly-β-hydroxybutyrate (PHB) and sulfur granules are examples of which type of bacterial component?

A.

Microcompartments

B.

Gas Vesicles

C.

Storage Granules

D.

Cytoskeletal elements