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Smartwork Chapter 3 Problems
Terms in this set (55)
Which of the following scenarios would cause a peritrichously flagellated bacterium (like E. coli) to swim in a forward motion?
all flagella turning counterclockwise.
Upon reorienting after a tumble, an E. coli cell
points itself in a random direction.
Compared to a random walk, a biased random walk has ______________ runs and a _____________ frequency of tumbling.
longer / decreased
Aspirin, like many pharmaceutical drugs, can access the cell because it is a weak acid. This occurs because
as a weak acid it can cross the membrane when in its uncharged form.
Weak acids and bases can occur in charged and uncharged forms. When charged they cannot cross the membrane, but they can when uncharged.
The lipopolysaccharides are found in the
outer cell membrane
The lipopolysaccharides are only found in the outer membrane of Gram-negative bacteria.
In the image below of a dividing bacterium, what structure is indicated by the arrows?
septum, which forms the division between the two new cells.
can propel bacteria toward a food source
Bacterial flagella can move the bacteria in a directed fashion termed "chemotaxis." The energy for flagellar rotation is provided by the proton motive force. Bacterial flagella differ in structure from eukaryotic flagella. Bacterial flagella rotate while eukaryotic flagella move in a whip-like motion.
The major function of the cell wall is to
serve as a rigid barrier to prevent cell lysis.
The cell wall is highly porous to molecules and does not provide for bacterial mobility. It does help the bacterial cell withstand interior turgor pressure and thus helps prevent cell lysis. The cell wall continues to expand to accommodate bacterial cell growth.
Phospholipids with an ether link between glycerol and the fatty acids are found in
Archaean phospholipids contain an ether link that strengthens the membrane. In bacteria and eukaryotes, such as plants and fungi, an ester link bridges the link between fatty acids and glycerol.
Label Bacterial Lipopolysaccharide
Which portion of LPS is most responsible for its toxic effects?
Because LPS has potent immunostimulatory effects, it is also known as endotoxin.
Correct! You can see this becomes a problem when attempting to use antibiotics to treat severe infections caused by Gram-negative bacteria.
A bacterial species is discovered that contains thylakoids and carboxysomes. It can be assumed from the presence of these structures that this bacterium
The presence of thylakoids (intracellular membranes containing photosynthetic pigments) and carboxysomes (containing carbon-fixation enzymes) suggests that the organism is photosynthetic.
Which of the following structures does not play a role in adherence of bacteria to surfaces and/or host cells?
Bacteria have evolved many mechanisms that allow them to attach and grow on surfaces. In fact, it is generally the preferred mode of growth, alternating only intermittently with a free-living (planktonic) phase.
Which of the following are characteristics of archaeal cell membranes that probably help them survive at very high temperatures?
Several mycobacterial species are pathogenic for humans, including Mycobacterium leprae (the causative agent of leprosy) and Mycobacterium tuberculosis. Recent studies have shown that asymmetry during cell division results in subpopulations of either rapidly elongating or slowly elongating cells (termed "accelerators" and "alternators," respectively). Researchers are now interested in how cell polarity and resulting physiological differences may influence the effectiveness of certain antibiotics used to treat mycobacterial diseases.
Isoniazid inhibits mycolic acid synthesis and is a first-line antibiotic used to treat tuberculosis. How would you predict accelerators and alternators might vary in their sensitivity to this drug?
Accelerators should be more sensitive than alternators.
Could you also now predict whether penicillin is more effective against actively growing or dormant bacterial cells?
Why do bacteria usually contain an even number of replisomes?
Because replication is bidirectional, there are two replication forks emanating from the origin of replication.
As DNA unwinds at the origin of replication, replication proceeds in both directions around the genome. This bidirectional replication requires two replisomes, one for each replication fork. Each replisome contains two DNA polymerases, one for each strand of DNA.
Reports of disease caused by enteropathogenic E. coli and its relative, Salmonella, usually include a description of the responsible serotype. For example, in 1993, hundreds of infections from Shiga-toxin-producing E. coli resulted from undercooked hamburgers sold by Jack-in-the-Box restaurants. The outbreak was caused by the now-infamous E. coli strain O157:H7. The "O" in this designation refers to an antigen on which of the following molecules?
The O-antigen is actually part of the lipopolysaccharide (LPS) component of the outer leaflet of the outer membrane of Gram-negative bacteria such as E. coli and Salmonella. Recall that LPS is composed of a lipid portion (lipid A) embedded in the bilayer as well as sugar chains that extend away from the cell. The long O-antigen polysaccharide is connected to lipid A via a core polysaccharide. Because the "H" refers to a flagellin, O157:H7 identifies a strain with a specific combination of LPS and flagellar antigens.
All cells are made up of water and essential ions as well as small and large organic molecules. Order the following components in E. coli during balanced exponential growth from greatest to least in terms of percentage of total cellular weight.
water > Protein > Nucleic acids > Lipids > Inorganic ions
If based on molcule amount:
water > Inorganic ions > Protein > Nucleic acids > Lipids
The idea that the bacterial genome is "loose" in the cytoplasm is incorrect because
the DNA is attached to the cell envelope and organized into domains through supercoiling and DNA-binding proteins.
Prokaryotic cells like bacteria are defined by not having a nucleus, but the DNA is organized in several ways, including attachment to the envelope, supercoiling, and DNA binding proteins arranging the genome into domains. The circular chromosome may be regionally condensed, but not the whole thing. Ribosomes bind mRNA during translation to produce proteins.
Many bacteria adapt to adverse environmental conditions by modifying the composition of their cell membranes. For example, the membranes of bacteria subjected to heat stress often contain high levels of which of these compounds?
saturated fatty acids
Saturated fatty acids are able to pack closely together in the lipid bilayer, enhancing membrane rigidity. High levels of these compounds can therefore help to preserve membrane integrity under conditions of thermal stress (and accompanying increased molecular motion).
Antibiotics that weaken the peptidoglycan cell wall make a bacterium more prone to
Bacterial cells typically live in habitats of lower osmolarity (solute concentrations) than that of their internal cytoplasm. The mesh-like peptidoglycan layer prevents swelling and lysis, which would otherwise occur in dilute environments.
The terms "peritrichous," "lophotrichous," and "monotrichous" describe the
distribution of flagella around a bacterium.
Peritrichous bacteria have randomly distributed flagella, and lophotrichous bacteria have flagella at one or both ends. Monotrichous bacteria have a single flagellum.
The FtzZ protein, found in both coccoid and rod-shaped bacteria, is important for maintaining the cell's
Movement of molecular oxygen (O2) and carbon dioxide (CO2) across the cell membrane
occurs by passive diffusion.
Interestingly, certain microorganisms, such as cyanobacteria, which require CO2 for photosynthesis, also use active transport to accumulate inorganic carbon (as CO2 or HCO3-) when external levels are limiting.
The arrangement of mycolic acids in the cell envelopes of mycobacteria allows them to function as a type of
The bacterial flagellum is most like which of the following?
Unlike eukaryotes, prokaryotes do not undergo mitosis or meiosis. Instead, most prokaryotes grow by a process known as binary fission, whereby an individual cell produces two identical daughter cells, each with its own chromosome.
Order the following events as they occur from beginning to end during DNA replication in a dividing cell.
DNA at origin unzips, and two replication forks form
Replisomes synthesize daughter chromosomes bidirectionally
terminator site is replicated
Daughter cells separate
What type of enzyme in the replisome catalyzes addition of nucleotides to the growing DNA strands?
Regarding the enzyme in Part 2,
______ of these would be required if a new round of DNA replication began before the first one terminated.
Which of the following is true of the newly synthesized daughter chromosomes?
Each chromosome contains one parental and one newly synthesized DNA strand.
Which class of molecules can directly cross the cell membrane without the aid of transport proteins?
Polar sugars and charged amino acids and ions cannot directly cross the cell membrane. Uncharged gasses can directly cross the cell membrane.
A Gram-negative cell envelope contains
an inner cell membrane, thin peptidoglycan layer, and outer membrane.
Gram-positive cell envelope contains a thicker layer of peptidoglycan surrounding its cell membrane, but lacks an outer membrane.
Cells of a normally rod-shaped bacterium (e.g., Bacillus subtilis) that have completely lost the ability to produce the MreB protein would mostly likely be
Cells that are normally coccoid-shaped (e.g., Staphylococcus) do not produce MreB. Thus, the coccus can be thought of as the "default" cell shape.
A second, outer membrane is found in
The bacterial cell wall is composed mainly of
Which of the following materials are commonly stored by bacteria for future metabolic needs?
C. polyhydroxybutyrate (PHB)
D. elemental sulfur (S0)
Many bacteria also accumulate polyphosphate (a storage form of inorganic phosphate). PHB-based plastics are of commercial interest because they are nontoxic and biodegradable.
Nucleus with a nuclear membrane
DNA replication and gene expression are separated
DNA replication and gene expression can occur simultaneously
Eukaryotes & Prokaryotes
DNA is genetic material for both
Ribosomes translate mRNa into protein
An actively dividing bacterial cell (such as E. coli) typically contains two molecules of
_____ and only one molecule of
______ , each of which constitutes approximately 1% of total cell weight.
DNA , peptidoglycan
In actively growing bacterial cells, fission occurs more quickly than the genomic DNA can be completely replicated. The cell solves this problem by creating multiple replication forks such that DNA synthesis is ongoing even during division. The result is an average of two chromosomes per cell during active growth.
The peptidoglycan layer exists as a single, large, flexible molecule exterior to the plasma membrane. It provides critical strength and resilience to the cell wall.
Which of the following are characteristics of archaeal cell membranes that probably help them survive at very high temperatures?
more than one:
B. cyclopentane rings
C. membrane monolayers
E. ether-linked lipids
These membrane adaptations allow hyperthermophilic archaea to live in environments such as geothermal hot springs and hydrothermal vents. Recognize, however, that although all archaea contain terpenoids ether-linked to glycerol, the tetraethers (i.e., monolayers) are more characteristic of those inhabiting extreme environments.
Gram-negative and Gram-positive cell envelope and place the labels on the correct targets.
You have isolated a microorganism from seawater that contains thylakoid membranes, gas vacuoles, and carboxysomes. It is most likely
Bacterial plasma (cell) membranes contain which two molecules in the greatest abundance?
Membrane proteins also generate and maintain ion gradients, aid in motility, and allow the cell to sense and respond to changes in its environment, among other functions.
Label the following illustration of a bacterial cell (plasma) membrane
Which of the following statements regarding the bacterial sacculus are true?
A sacculus is another name for the bacterial cell wall. It is actually one very large molecule of peptidoglycan that surrounds the cell membrane of nearly all bacteria. It protects the cell from osmotic lysis and confers a particular shape on the bacterial cell (e.g., rod or coccus).
B. It provides protection from osmotic rupture.
D. It is also known as the cell wall.
E. It is composed of peptidoglycan.
Examine the following illustration of cross-bridge formation during construction of the peptidoglycan cell wall (in this case, from E. coli) and place the labels on the correct targets.
In bacterial cells,
transcription, translation, and DNA replication can all occur at the same time in the same cell compartment.
Certain aquatic bacteria use magnetosomes to direct them to environments with optimal levels of
Magnetotactic bacteria require environments containing little to no oxygen. By orienting to magnetic north, net movement is directed down into pond sediments, which are ideal habitats for these organisms.
Vinegar has preservative and antimicrobial properties due to the ability of the active ingredient to cross the membrane as ______________. Once in the cytoplasm, it becomes _______________, thereby, disturbing normal pH.
Which of the following cellular components is considered an endotoxin that is harmless as long as the pathogen remains intact but when released by a lysed cell overstimulates host defenses, which may result in a lethal endotoxic shock?
listed below are characteristic of all bacteria, and which are specialized structures found in only some bacteria?
If a bacterial species lacks a cell wall, a reasonable prediction about the environment where this species lives is that it
experiences a constant solute concentration.
The cell wall protects against osmotic shock. This would be unnecessary in an environment with unchanging osmotic pressure.
Penicillin's mode of action is to inhibit
cell wall cross-link formation.
Penicillin inhibits the transpeptidase that cross-links peptidoglycan peptides. Other antibiotics may target ribosomal subunits.
The most abundant molecule in the cell is
The model bacterium E. coli is about 70% water by weight.
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