Micro chapter 3 from readings and quizzes

Polar aging can cause members of the population to die as they accumulate damaged proteins at the "old" end of the cell. Some types of cells overcome this issue byChoose one: A. alternating fast and slow extension of the poles. B. delaying nutrient uptake to prevent protein accumulation. C. delocalizing polar marking proteins like TipN. D. resynthesizing the whole sacculus.

A. alternating fast and slow extension of the poles. By only extending at one pole (alternating fast and slow to enable this), the resulting poles of each cell are of different ages throughout the population, preventing "very old" poles to occur. Resynthesizing the whole wall would be very uncommon and energetically expensive; TipN is used to allow polar differentiation but does not prevent aging; and delayed nutrient uptake is due to the type of cell wall, not its age.

The bacterial flagellum is most like which of the following? Choose one: A. corkscrew B. snake C. wheel D. whip E. whale tail

A. corkscrew Correct! The bacterial flagellum is a rigid, helical structure—much like a corkscrew or boat propeller. It bears very little similarity (in structure or mode of motion) to eukaryotic flagella.

A bacterial species is discovered that contains thylakoids and carboxysomes. It can be assumed from the presence of these structures that this bacterium Choose one: A. is capable of photosynthesis. B. is pathogenic. C. can orient along Earth's magnetic fields. D. can attach to a nonliving substrate.

A. is capable of photosynthesis.

Supercoiling of DNAChoose one: A. may be affected by antibiotics. B. is unnecessary to fit the DNA into the cell. C. occurs only in prokaryotes. D. is an energy-independent process that happens spontaneously.

A. may be affected by antibiotics.

Eukaryotic genomes comprise mostly __________, whereas prokaryotes have mostly __________.Choose one: A. noncoding DNA; coding DNA B. positively supercoiled DNA; negatively supercoiled DNA C. double-stranded DNA; single-stranded DNA D. circular DNA; linear DNA

A. noncoding DNA; coding DNA

As temperatures drop, membrane fluidity decreases. Which of the following changes to phospholipids will help maintain correct bacterial membrane fluidity under cold temperatures? Choose one: A. An increase in unsaturated fatty acids B. Cyclization of part of the fatty acid chain to form a planar ring C. A switch from ester linkages between fatty acids and glycerol to ether linkages D. An increase in the length of the fatty acid tails

A. An increase in unsaturated fatty acids

Why do bacteria usually contain an even number of replisomes?Choose one: A. Because replication is bidirectional, there are two replication forks emanating from the origin of replication. B. DNA is double-stranded and each single strand requires its own replisome. C. Bacteria need only one replisome; the other serves as a backup copy. D. There are two copies of the gene that codes for DNA polymerase, an important enzymatic protein component of replisomes.

A. Because replication is bidirectional, there are two replication forks emanating from the origin of replication.

Which structures connect neighboring bacterial cells to facilitate exchange of cytoplasmic contents?Choose one: A. Nanotubes B. Stalks C. Pili D. Capsules E. Membrane vesicles

A. Nanotubes Correct! Intercellular nanotubes allow sharing of nutrients, antibiotic resistance determinants, and facilitate electron transfer between neighboring cells.

The idea that the bacterial genome is "loose" in the cytoplasm is incorrect because Choose one: A. the DNA is attached to the cell envelope and organized into domains through supercoiling and DNA-binding proteins. B. the DNA is usually condensed into a chromosome. C. attached ribosomes prevent tangling of the DNA. D. bacterial cells have a nucleus.

A. the DNA is attached to the cell envelope and organized into domains through supercoiling and DNA-binding proteins.

Which statement concerning the genomes of organisms is true? Choose one: A. Archaeal genomes are larger than bacterial genomes. B. Organisms differ in their genome size. C. Organisms differ in DNA content but contain roughly the same number of genes. D. All organisms have roughly the same DNA content.

B. Organisms differ in their genome size.

Which one of the following proteins would be found in the outer membrane of Gram-negative bacteria? Choose one: A. Amino acid synthetic enzymes B. Peptide porins C. Amino acid transporters D. ATP synthase

B. Peptide porins The outer membrane is not as selective as the inner membrane. It contains porins that admit larger molecules. Both ATP synthase and amino acid transporters are found in the inner membrane. Amino acid synthetic enzymes are cytoplasmic.

Which of the following structures does not play a role in adherence of bacteria to surfaces and/or host cells?Choose one: A. flagella B. carboxysomes C. pili (fimbriae) D. extracellular polysaccharides E. stalk and holdfast

B. carboxysomes

The cell structure immediately external to the cytoplasm is the Choose one: A. periplasm. B. cell membrane. C. cell wall. D. outer membrane.

B. cell membrane. The cell membrane is in contact with the cytoplasm. All the other structures listed, if present, are external to the cell membrane.

The terms "peritrichous," "lophotrichous," and "monotrichous" describe the Choose one: A. means by which a bacterium obtains energy. B. distribution of flagella around a bacterium. C. shape of bacterial cells. D. distribution of the nucleoid within a bacterium.

B. 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.

If a bacterial species lacks a cell wall, a reasonable prediction about the environment where this species lives is that it Choose one: A. undergoes extreme temperature fluctuations. B. experiences a constant solute concentration. C. is rich in nutrients. Since the microbe can divide rapidly, a cell wall would get in the way. D. experiences a constant temperature.

B. experiences a constant solute concentration. The cell wall protects against osmotic shock. This would be unnecessary in an environment with unchanging osmotic pressure.

In most bacterial species the DNA isChoose one: A. single-stranded. B. negatively supercoiled. C. positively supercoiled. D. enclosed in a nuclear membrane called the nucleoid.

B. negatively supercoiled.

The bacterial cell wall is composed mainly of Choose one: A. chitin. B. peptidoglycan. C. cellulose. D. lipopolysaccharides.

B. peptidoglycan. Peptidoglycan is a major component of bacterial cell walls. Cellulose is found in plant cell walls and chitin in fungal cell walls. Lipopolysaccharides are found in the outer membrane of Gram-negative bacteria.

The major function of the cell wall is to Choose one: A. allow for bacterial motility. B. serve as a rigid barrier to prevent cell lysis. C. serve as a barrier to prevent entry of molecules into the cytoplasm. D. constrain bacterial cell growth.

B. 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.

Which of the following processes occurs in stalked (but not swarmer) Caulobacter cells?Choose one: A. nutrient transport B. translation C. DNA replication D. motility E. transcription

C. DNA replication The motile swarmer cell form of Caulobacter is incapable of division, but in favorable habitats, it loses its flagellum and attaches to a surface via a holdfast. The attached end then elongates into a stalk and DNA synthesis is initiated, followed by septation and release of a flagellated swarmer cell.

Which of the following is NOT a function of the cell membrane?Choose one: A. Separation of charge across the membrane B. Transport of molecules into and out of the cell C. Production of proteins D. Detection of environmental signals

C. Production of proteins

Which class of molecules can directly cross the cell membrane without the aid of transport proteins? Choose one: A. Amino acids B. Ions C. Uncharged gasses D. Sugars

C. Uncharged gasses Polar sugars and charged amino acids and ions cannot directly cross the cell membrane. Uncharged gasses can directly cross the cell membrane.

The fatty acids found in bacterial phospholipids are Choose one: A. all saturated fatty acids. B. identical to fatty acids found in eukaryotic phospholipids. C. a mix of saturated and unsaturated fatty acids. D. all unsaturated fatty acids.

C. a mix of saturated and unsaturated fatty acids.

Phospholipids with an ether link between glycerol and the fatty acids are found in Choose one: A. bacteria. B. plants. C. archaea. D. fungi.

C. archaea. 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.

Aspirin, like many pharmaceutical drugs, can access the cell because it is a weak acid. This occurs because Choose one: A. it disrupts the membrane enough to squeeze through. B. it is a small uncharged molecule. C. as a weak acid it can cross the membrane when in its uncharged form. D. it is carried by water during osmosis.

C. 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.

Bacterial flagella Choose one: A. move in a whip-like fashion. B. do not require any energy to move. C. can propel bacteria toward a food source. D. are identical in form and function to eukaryotic flagella.

C. 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.

Bacteria make extensive use of secreted extracellular signals for sensing the presence of other cells. Which of the following structures represents a more direct method of communication between individual cells? Choose one: A. fimbriae B. capsules C. nanotubes D. flagella E. pili

C. nanotubes Correct! Cytoplasmic molecules, and even some types of plasmids, can pass from one cell to another through these bridges.

The lipopolysaccharides are found in theChoose one: A. cytoplasm. B. periplasm. C. outer membrane. D. inner membrane.

C. outer membrane.

Most species of bacteria cannot be eaten by humans because the bacteria contain Choose one: A. toxic phospholipids in their membranes. B. water levels that would stress the kidneys. C. toxic levels of nucleotides. D. toxic levels of proteins.

C. toxic levels of nucleotides. Many bacterial species may be 8% by weight nucleotides, levels much higher than those found in eukaryotes. Such high levels of nitrogen-containing nucleotides are toxic to humans.

In bacterial cells, Choose one: A. transcription and translation occur together but not while DNA replication is occurring. B. transcription and DNA replication can occur together, but translation is spatially separate from transcription and replication. C. transcription, translation, and DNA replication can all occur at the same time in the same cell compartment. D. transcription, translation, and DNA replication are all spatially separate.

C. transcription, translation, and DNA replication can all occur at the same time in the same cell compartment.

Could two bacteria share protein complexes via nanotubes? What about hydrogen molecules (H2) as electron donors?

Cells have been shown to share proteins via nanotubes, such as enzymes for carbohydrate catabolism. In principle, a nanotube could be wide enough to allow transmission of ribosomes. However, nanotubes could not share dihydrogen molecules, because H2 is a gas that penetrates membranes and would escape through the nanotube walls.

A Gram-negative cell envelope contains Choose one: A. a thick layer of peptidoglycan only. B. a double membrane, but no peptidoglycan cell wall. C. a cell membrane covered by a thick layer of peptidoglycan. D. a thin layer of peptidoglycan surrounded by a cell membrane. E. an inner cell membrane, thin peptidoglycan layer, and outer membrane.

E. an inner cell membrane, thin peptidoglycan layer, and outer membrane. In contrast, a Gram-positive cell envelope contains a thicker layer of peptidoglycan surrounding its cell membrane, but lacks an outer membrane.

What do you think happens to two single-stranded DNA molecules isolated from different genes when they are mixed together at very high concentrations of salt? Hint: High salt concentrations favor bonding between hydrophobic groups.

In high salt conditions, the stacking of hydrophobic bases is so strongly favored that two single strands of DNA will form a duplex no matter what the sequence of base pairs is.

penicillin binds targets what type of proteins?

the transpeptidase that cross-links the peptides is the target

starvation stress increases bacterial production of what kinds of lipids?

those with an unusual type of phosphoryl head group like cardiolipin (a double phospholipid linked by a glycerol that concentrates at patches called domains)

what kind of microscopy reveals how cell parts fit within the cell as a whole?

transmission electron microscopy

Membrane-permeant weak acids and weak bases cross the membrane in their ______ form

uncharged (HA (weak acid) or B (weak base)) (the acids and bases dissociate inside the cell)

The most abundant molecule in the cell is Choose one: A. proteins. B. lipids. C. DNA. D. water.

water The model bacterium E. coli is about 70% water by weight.

what type of microscopy revels the location and dynamics of individual cell components?

fluorescnence microscopy

Which chemicals do we find in the greatest number in a bacterial cell? The smallest number?

greatest: inorganic ions (250 million / cell) smallest: DNA molecules (one large molecule, branched during replication)

Evidence suggests that organic carbon released in membrane vesicles by the marine cyanobacterium Prochlorococcus, contributes to their survival by attracting:Choose one: heterotrophic bacteria bacteriophage protists other cyanobacteria

heterotrophic bacteria Other proposed roles for membrane vesicles include facilitating horizontal gene transfer and acting as phage "decoys"

Why would laboratory culture conditions select for evolution of cells lacking an S-layer?

in a laboratory test tube free of predators or viruses, mutant bacteria that fail to produce the thick protein layer would save energy

is there more solute inside or outside cells?

inside (causes more water to enter the cell through osmosis)

one side (layer) of the phospholipid bilayer is called a _____

leaflet

why do some antibiotics like triclosan (from detergents and cosmetics), target enzymes like enoyl reductase which are responsible for fatty acid synthesis?

lipids are key components of bacterial cell membranes that regulate what can enter the cell. by destroying lipid makers, the anibacterial substance can enter the cell and kill it

Certain aquatic bacteria use magnetosomes to direct them to environments with optimal levels of _________

oxygen 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.

what are hopanoids

pentacylic (5-ring) hydrocarbon derivatives that fit between the fatty acid side chains of membranes and limit their motion

Binary division in seemingly symmetrical cells does not always yield identical daughter cells. For example, E. coli cells subjected to antibiotic or acid stress will sequester irreversibly damaged ______at the "older" pole. This strategy enhances survival of the younger cells in adverse conditions.

proteins By storing these defunct proteins at the older cell pole, the cell gives its younger progeny a better chance of survival.

sacculus

the bacterial cell wall

what are the benefits of the enhanced fluidity of the cell membrane from the kinked unsaturated fatty acids in phospholipids?

the enhanced fluidity of a kinked phospholipid improves the function of the membrane at low temperature; hence, bacteria can respond to cold and heat by increasing or decreasing their synthesis of unsaturated phospholipids

what is septation

the formation of the septum (the partition that divides the bacterial cell envelope) managed by a protein called divisome

what molecules can enter cells through simple diffusion

- uncharged molecules - O2 - CO2 - water (but their rate of passage can increase through aquaporins)

Suppose a cell has a defect in its ftsZ gene. What might happen to the cell during growth? How could such a mutant strain be maintained in the laboratory?

A cell with a defective ftsZ gene will fail to septate. As the cell grows, it expands and replicates its DNA, but no septum forms and the daughter cells do not separate. Eventually, the cell's nucleoids will entangle and the long, filamented cell chain will die. There are several ways to maintain an ftsZ mutant in a viable state. One is to use a temperature-sensitive mutant, in which the FtsZ protein is functional at the permissive temperature but nonfunctional at the nonpermissive temperature. Another way is to maintain a copy of the ftsZ gene fused to a promoter that can be turned on or off by the presence of an inducer molecule such as a sugar (discussed in Chapter 10).

What other ways can you imagine that bacteria might mutate to become resistant to vancomycin?

A common means of resistance to antibiotics is to pump them out of the cell. A protein pump that exports other molecules might mutate to capture vancomycin and export it from the cell. Another possibility is that an enzyme could modify the vancomycin by adding phosphoryl groups or acetyl groups, which would prevent the antibiotic from binding the alanine dipeptide. Still another possibility is that the bacteria might evolve a thicker cell wall that would exclude the vancomycin from the inner layers of peptidoglycan.

Antibiotic resistance in Mycobacterium tuberculosis is a global health concern. It can arise very rapidly in this microbe becauseChoose one: A. the process of cell division produces cells of varying age classes, each having different structural and metabolic properties, allowing different cells in the population to be resistant to different antibiotics. B. it has a very high mutation rate compared to other microbes and so antibiotics will become less effective more rapidly. C. the rapid rate of cell division overwhelms the antibiotic available. D. the complex outer envelope is always changing, making antibiotic resistance more likely.

A. the process of cell division produces cells of varying age classes, each having different structural and metabolic properties, allowing different cells in the population to be resistant to different antibiotics. M. tuberculosis has a complex outer envelope, but it is not changing rapidly and it slows cell division. The mutation rate is not likely to be greater in this group than any other.

The bacterial cytoskeletal proteins FtsZ and MreB are homologous to the eukaryotic __________ and __________, respectively. Choose one: A. tubulin; actin B. spindle; intermediate filament C. myosin; actin D. microtubule; microfilament

A. tubulin; actin The cytoskeletal proteins of bacteria are analogous to the eukaryotic tubulin and actin, which make up microtubules, intermediate filaments, and microfilaments found in eukaryotic cells. The spindle is made of microtubules. Myosin is a motor protein associated with actin filaments.

Which of the following scenarios would cause a peritrichously flagellated bacterium (like E. coli) to swim in a forward motion? A. 50% or more of the flagella rotating counterclockwise B. rotation of the flagella (direction doesn't matter) on only the "back" half of the bacterium C. 50% or more of the flagella rotating clockwise D. all flagella turning counterclockwise E. all flagella turning clockwise

Correct! Alternatively, a rotational shift (to clockwise) in the flagellar motor of even one flagellum will cause the entire bundle to fly apart, and the cell will tumble. D. all flagella turning counterclockwise

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?Choose one: A. Inner membrane phospholipids B. Periplasmic proteins C. The cell wall D. Lipopolysaccharides

D. Lipopolysaccharides

You have isolated a microorganism from seawater that contains thylakoid membranes, gas vacuoles, and carboxysomes. It is most likely Choose one: A. algae. B. Caulobacter. C. E. coli. D. a cyanobacterium. E. an ameba.

D. a cyanobacterium.

The surface layer (S-layer) of prokaryotesChoose one: A. is present all the time in all bacteria. B. is composed primarily of saccharin. C. is found only in archaea. D. may be lost from bacteria cultured in the lab.

D. may be lost from bacteria cultured in the lab. The S-layer is found in many free-living prokaryotic species. However, due to lack of selection pressure, the S-layer may be lost in cultured bacteria.

Caulobacter crescentus has asymmetrical cells, where one pole is plain and the other can have either a flagellum or a stalk. The difference between the poles isChoose one: A. the presence of nutrients at one end of the cell. B. the presence of storage granules. C. accumulated protein aggregates. D. the presence of a protein marker TipN marking the pole for a cellular extension.

D. the presence of a protein marker TipN marking the pole for a cellular extension. While old poles accumulate protein aggregates, what marks the pole for organelles in C. crescentus is the presence of the TipN protein. Nutrients can trigger which organelle is produced, and storage granules are a specialized structure unrelated to polar differentiation.

The discovery of _________ in membrane vesicles released from Prochlorococcus suggests a role for these elements in horizontal gene transfer.

DNA

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.

bacterial cells contain many enzymes that can degrade linear DNA. How, then, do linear chromosomes in organisms like Borrelia burgdorferi avoid degradation?

DNA- digesting exonucleases act on free 5' or 3' ends. The Borrelia linear chromosomes possess covalently closed hairpin ends called teloeres and do not possess free 5' or 3' groups

_________ (Gram-positive) have a thick cell wall with 3-20 layers of peptidoglycan, interpenetrated by teichoic acids (Fig. 3.15A). The phylum _________ consists of Gram-positive species such as Bacillus thuringiensis and Streptococcus pyogenes, the cause of strep throat.

Firmicutes

what are the components of a divisome and their functions

FtsZ - polymerizes to form a z ring FtsN - helps regulate the timing of constriction of the septum - without them, membranes will balloon out during cell division

________ of the phylum Actinomycetes have a complex, multilayered envelope that includes defensive structures such as mycolic acids. Examples include Mycobacterium tuberculosis (the cause of tuberculosis) and M. leprae (the cause of leprosy).

Mycobacteria

__________ (Gram-negative) have a thin cell wall with one or two layers of peptidoglycan, enclosed by an outer membrane (Fig. 3.15B). Included among these bacteria are Gram-negative species such as Escherichia coli and nitrogen-fixing Sinorhizobium meliloti.

Proteobacteria

DNA gyrase is essential to cell viability. Why, then, are nalidixic acid-resistant cells that contain mutations in gyrA still viable?

The gyrA mutations alter only the nalidixic acid-binding site on GyrA, not its gyrase activity. In other words, active DNA gyrase is still made, but the drug cannot bind to it.

the membranes of ______ or _______ may stain Gram-positive, Gram-negative, or variable

cyanobacteria an spirochetes

How do the kinetics of denaturation and renaturation depend on DNA concentration?

The speed of denaturation does not depend on DNA concentration, but the speed of renaturation does. The higher the concentration of ssDNA, the more likely it is that complementary sequences will find each other and the faster the duplex can re-form.

S-layer

a tough surface layer a crystalline sheet of thick subunits consisting of protein or glycoprotein (proteins with attached sugars) lost after repeated cell culturing

what about their membranes allows archea to survive in much higher temperatures?

all archael phospholipids replace the ester link between glycerol and fatty acid with an ether link, which is much more stable archael hydrocarbon chains are branched terpenoids - strengthens the membrane and limits movement of hydrocarbons (less movement and less fluidity is better for hot environments)

Bacteria convert unsaturated fatty acids to _______ during starvation and acid stress, conditions under which membranes require stiffening.

cyclopropane

periplasm

aqueous compartment between outer membrane and plasma membrane

The membrane lipids of ______ differ fundamentally from those of bacteria and of eukaryotes

archaea

Amino acids have acidic and basic groups that can dissociate. Why are they not membrane-permeant weak acids or weak bases? Why do they fail to cross the phospholipid bilayer?

at a neutral pH, an amino acid has both a positively charge amine and a negatively charged carboxylate charged ions CANNOT freely pass through the plasma membrane in an amino acid, if a charged group becomes neutralized by acid or base, the other group remains charged, so the molecules as a whole will never cross the membrane

Why does a cell contain 100 times as many lipid molecules as strands of RNA?

because lipids are small structural molecules, highly packed. They are a major component of the cellular membrane. RNA molecules are long macromolecules that either are packed into complexes (such as ribosomal RNA) or are temporary information carriers (messenger RNA), present only as needed to make proteins.

why are enzymes of septum biosynthesis of interest for the development of antibiotics?

because the site of septation is vulnerable because two new large enclosures must form simultaneously in order for division to occur

How does a cell distinguish itself from what is outside/ what structure defines its existance of the cell?

cell membrane

what does a bacterial cell envelope contain?

cell membrane and thick peptidoglycan cell wall (gram negative bacteria also contain outer membranes in addition)

what is a Phosphatidylglycerol

consists of glycerol with ester links to two fatty acids, and a negatively charged phosphoryl group linked to a terminal glyceride

what is a Phosphatidylethanolamine

contains a glycerol linked to two fatty acids, and a phosphoryl group with a terminal ethanolamine. The ethanolamine carries a positive charge. (so can interact with DNA)