Microbiology Chapter 3 HW, Microbiology Chapter 4 Part 2 HW, Microbiology Chapter 4 Part 1 HW

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

A Bacteria have a single compartment, the cytoplasm, where transcription, translation, and replication can all take place at the same time.

If a bacterium can divide once an hour, then after 5 hours, 1 bacterium will have yielded __________ bacteria. Choose one: A. 32 B. 10 C. 5 D. 50

A If N0 is the initial number of bacteria, then the number of organisms after n generations will be N0 × 2n. Since we are told the generation time is 1 hour, 5 hours yields five generations. 1 × 25 = 32.

Which of the following materials are commonly stored by bacteria for future metabolic needs? Choose one or more: A. glycogen B. polyhydroxybutyrate (PHB) C. elemental sulfur (S0) D. nanotubes E. gas vesicles

A, B, & C Many bacteria also accumulate polyphosphate (a storage form of inorganic phosphate). PHB-based plastics are of commercial interest because they are nontoxic and biodegradable.

Which of the following is true of complex media? Choose one: A. Complex media can help determine the metabolic capacity of an organism. B. All the components and their concentrations are known. C. Bacteria grow faster on complex media than on synthetic media. D. Complex media are the most difficult of all to prepare.

C Complex media provide many of the chemical building blocks that a cell would otherwise have to synthesize on its own. Hence, they grow faster on complex media. Complex media are poorly defined, nutrient-rich media. They are usually easier to prepare than precisely defined synthetic media. Defined synthetic media can be used to help determine the metabolic capacity of an organism. For example, a specific amino acid or vitamin can be added to synthetic media to support the growth of organisms that lack the ability to produce it.

An essential nutrient is one that Choose one: A. is not needed by the bacteria for proper growth. B. is always plentiful in the environment. C. bacteria need for proper growth and can make themselves. D. bacteria need for proper growth but cannot make themselves.

D Essential nutrients are needed for proper bacterial growth and must be acquired from the environment, where they may or may not be plentiful.

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

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

In the image below of a dividing bacterium, what structure is indicated by the arrows? Choose one: A. The origin of replication B. The flagellum C. The replisome D. The septum

D The septum forms the division between the two new cells.

What type of enzyme in the replisome catalyzes addition of nucleotides to the growing DNA strands?Choose one: A. helicase B. recombinase C. transcriptase D. gyrase E. polymerase

E Along with its catalytic function, DNA polymerase III holoenzyme is able to proofread and correct mismatched bases in newly synthesized DNA. Other DNA polymerases in the cell are important for repairing damaged DNA.

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

E Cyanobacteria (formerly known as blue-green algae) were originally responsible for oxygenation of Earth's atmosphere and share a common ancestor with the chloroplasts of plants and green algae.

Biofilms are defined as microbial communities growing within a self-produced extracellular matrix composed primarily of Choose one: A. peptidoglycan. B. ejected flagella. C. fimbriae. D. waxy lipids. E. polysaccharides.

E Exopolysaccharide (or EPS) forms the protective matrix that insulates the bacteria from chemicals and phagocytes and makes them difficult to remove.

Regarding the enzyme in Part 2, _________ of these would be required if a new round of DNA replication began before the first one terminated.

Twelve The ability of prokaryotes to produce multiple replication forks permits generation times much faster than those required to actually replicate the DNA.

Place the nine steps of the dilution streaking technique in the correct order. - Remove a sample of bacteria from the culture flask (of plate) using the sterile loop. - Flame the loop a third time and allow it to cool. - Inoculate a section of your agar petri dish by sweeping the loop back and forth across the surface. - Using the loop, draw cells from the second area onto another fresh section of agar. - Sterilize the loop (an allow it to cool) before using it to obtain the bacterial inoculum. - Sterilize the loop for a final time. - Using the loop, streak cells from the first area onto a fresh section of agar. - Place the petri plate in the appropriate incubator. - Flame the loop a second time and allow it to cool.

1. sterilize the loop ( & allow to cool), use it to obtain bacterial inoculum 2. remove sample bacteria from culture flask/plate using sterile loop 3. inoculate section of agar petri dish by sweeping loop back & forth across surface 4. flame loop 2nd time & allow to cool 5. using loop, streak cells from 1st area onto fresh section of agar 6. flame loop 3rd time & allow to cool 7. using loop, draw cells from 2nd area onto another fresh section of agar 8. sterilize loop final time 9. place correct petri dish plate in incubator

A food worker was preparing some macaroni salad on the same counter on which he had cut up some raw chicken. Suppose this resulted in the accidental introduction of 380 cells of E. coli into the 1 gallon container of macaroni. This careless worker then left it unrefrigerated until 6 hours later. Now consider that E. coli has a doubling (generation) time of 20 minutes when grown in a rich medium. Assuming the cells were dividing at their maximum rate in the macaroni salad, what would the level of bacterial contamination be by the time it was finally refrigerated? ________ cells

99614720 cells

Which of the following statements is true? Choose one: A. All organisms require carbon as a macronutrient. B. Most bacterial species can be cultured in the lab. C. Bacterial species use a limited number of nutrient sources. D. All bacterial species require the same nutrients for growth.

A Bacteria have evolved to be able to use a wide variety of different compounds as nutrient sources and may have different essential nutrient requirements. Many bacteria are unculturable if their specific requirements are not met in the laboratory or if their niche cannot be readily recreated, such as in the case of intracellular parasites. Carbon is the basis of organic compounds and is a macronutrient for all life forms.

You have isolated a mutant strain of Bacillus subtilis (which you designate wimP) whose endospores can be killed by boiling water. When you analyze the endospores produced by this strain, you find that compared to endospores produced by the parent (a wild-type strain), the wimP spores have significantly Choose one: A. higher water content. B. lower amounts of spore coat proteins. C. reduced amounts of germination factors. D. elevated amounts of germination factors. E. reduced amounts of small acid-soluble proteins.

A Because proteins denature more easily in moist heat, the ability of endospores to survive heat is inversely related to their water content. In fact, endospores typically contain only 10-30% of the free water that a vegetative cell does. Dipicolinic acid normally aids in the dehydration of endospores and also protects its DNA.

The cell envelopes of mycobacteria contain large amounts of these molecules, which make them "acid-fast." Choose one: A. mycolic acids B. arabinogalactans C. peptidoglycans D. fibronectin-binding proteins E. teichoic acids

A Cells containing mycolic acids are both hard to stain (usually the dye needs to be driven in with moist heat), and once stained, the cells are difficult to decolorize (even with acid).

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 Choose one: A. coccoid-shaped. B. unable to divide symmetrically. C. filamentous in form. D. stalked (like Caulobacter). E. nonflagellated.

A 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.

Part 3: What is the role of dipicolinic acid in endospore formation? Choose one: A. It aids in dehydration of the endospore and enhances heat resistance. B. It is the major component of the endospore cortex. C. It directs assymetrical septum formation. D. It lyses the mother cell during endospore release. E. It induces sporulation.

A Dipicolinic acid, complexed with Ca2+, binds free water to cause dehydration of the endospore. Having less moisture contributes to the endospore's heat resistance. The dipicolinic acid-Ca2+ complex also binds to the endospore's DNA, helping to protect it from heat denaturation.

Movement of molecular oxygen (O2) and carbon dioxide (CO2) across the cell membrane Choose one: A. occurs by passive diffusion. B. occurs only unidirectionally, such that oxygen is allowed to enter and carbon dioxide (waste) is able to leave. C. requires energy in the form of ATP or the proton motive force. D. only occurs when the O and C atoms are part of some other molecule (e.g., a sugar or amino acid). E. occurs passively, but membrane transporters are required to facilitate their movement.

A 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.

Which key enzyme directly involved in the above process is not explicitly shown in the illustration?Choose one: A. RNA polymerase B. ATP synthase C. DNA polymerase D. sortase E. transpeptidase

A Just as many ribosomes can cotranslate a given transcript, so can multiple RNA polymerases transcribe the same gene, one following behind the other.

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

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

Mature biofilms of Pseudomonas aeruginosa produce flagellated cells for what purpose? Choose one: A. to go in search of new places to colonize B. to increase water and nutrient flow through biofilm channels via flagellar rotation (like a mini motor) C. to provide additional elevation to the biofilm towers (the flagella act as stalks) D. to escape grazers that may be foraging on the biofilm E. There is no real "purpose." Because of random mutations, some revert to a flagellated form.

A When nutrients levels drop, the biofilm matrix partially dissolves to free cells that have reverted to a motile form. The flagellated cells then swim off in search of new habitats to colonize.

Cellular synthesis of which of the following would be directly affected by nitrogen limitation? Choose one or more: A. Amino acids B. Nucleotides C. Fatty acids D. Simple sugars

A & B Because amino acids each have a nitrogen-containing amine group (-NH2), and nucleotides each contain a nitrogenous base joined to a 5-carbon sugar and phosphate group, these both require nitrogen for synthesis. Thus, they would be directly affected by nitrogen limitation.

Which of the following statements regarding the bacterial sacculus are true?Choose one or more: A. It is composed of peptidoglycan. B. The crucial cross-linking reactions occur inside the cell (i.e., in the cytoplasm). C. It is also known as the cell wall. D. It provides protection from osmotic rupture. E. It is impervious to polar or charged molecules.

A, C, & D 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).

Which of the following are characteristics of facilitated diffusion?Choose one or more: A. It involves substrate-specific carrier proteins. B. It only operates unidirectionally (to move solutes into the cell). C. It represents an important uptake system for bacteria living in dilute aquatic environments. D. Solutes are chemically modified (such as by addition of a phosphate group) as they enter the cell. E. It cannot internally concentrate a solute relative to the external environment. F. It does not require energy expenditure by the cell.

A, E, & F Facilitated diffusion contributes to the selective permeability of the membrane by allowing entry of substrates that would not otherwise freely move across the lipid bilayer. Specific carrier proteins are needed that facilitate the bidirectional movement of solutes along its concentration gradient.

Which of the cell components listed below are characteristic of all bacteria, and which are specialized structures found in only some bacteria? - DNA - Ribosomes - Stalks - Phospholipids - Carboxysomes - Pili - Gas vesicles - Flagella

All bacteria: - Phospholipids - DNA - Ribosomes Some bacteria: - Stalks - Flagella - Carboxysomes - Gas vesicles - Pili Nearly all bacteria (with the exception of some obligate parasites that have lost the trait) also possess a unique cell wall molecule composed of peptidoglycan.

Water molecules are sufficiently small that they do not require specific transporters to cross biological membranes. But because they are polar, diffusion of these molecules across the phospholipid bilayer is slow. Peter Agre won the 2003 Nobel Prize in Chemistry for his discovery that the rapid movement of water into and out of cells occurs via ____________

Aquaporins Originally discovered in human erythrocytes, aquaporins were referred to as "the plumbing system for cells" by Dr. Agre. With their discovery, the question of how water moves through cells was solved.

Despite the wide range of habitats in which they may form, biofilms form in a similar progression of stages. Label the piece of art with the labels that correspond to each stage of biofilm formation by dragging them to the correct targets. - Dissolution and dispersal - Attachment by flagella - Development of microcolonies - Mature biofilm - Planktonic cells - EPS matrix produced - Environmental cue to settle

Attachment monolayer, microcolonies, EPS, mature biofilm, dissolution and dispersal, planktonic cells, environmental cue to settle

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

B 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.

Antibiotics that weaken the peptidoglycan cell wall make a bacterium more prone to Choose one: A. shrinkage in hypertonic solutions. B. osmotic lysis. C. phagocytosis by macrophages. D. detaching from surfaces. E. starvation.

B 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.

Part 2: Which of the following statements is NOT true of sporulation? Choose one: A. The resultant endospores may remain viable for thousands of years. B. It represents an important form of reproduction for some bacterial species. C. The process is long and complex, requiring 8-10 hours. D. This capability is shared by many species of Gram-positive pathogens. E. Under favorable conditions, endospores can germinate and resume vegetative growth.

B Because bacterial sporulation typically results in only one endospore produced per cell, no net increase in cell number occurs.

Which of the following is true of cells in batch culture? Choose one: A. New batches of media are added during culturing. B. Cells will not remain at a constant mass. C. Metabolic wastes do not accumulate. D. Cells never reach exponential growth rates.

B During batch culturing, no new media are added. As nutrients are depleted and metabolic wastes accumulate, cell size may be reduced and the cells will enter a stationary phase.

Bacteria as a group are incredibly metabolically diverse, but individual species are often highly specialized to reduce competition in their natural environment. This results in these species being unculturable because Choose one: A. trace elements in the water used in the laboratory prevent their growth. B. their growth may depend on necessary growth factors provided by other organisms in their natural environment. C. components in laboratory media are toxic to them. D. they cannot tolerate oxygen.

B Growth factors are specific nutrients required by a species but not by others; they may be products of other organisms' metabolism and thus would not be provided in the laboratory. Meanwhile, anaerobes can be cultured under proper conditions. And though some media can have toxins present either from the media or the water used to produce them, it is possible to tailor recipes for fastidious microbes.

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. Periplasmic proteins B. Lipopolysaccharides C. The cell wall D. Inner membrane phospholipids

B Lipopolysaccharides are of crucial medical importance because they act as an endotoxin.

Penicillin's mode of action is to inhibit Choose one: A. DNA replication by allosterically binding to DNA polymerase. B. cell wall cross-link formation. C. translation by binding to the 50S ribosomal subunit. D. translation by binding to the 30S ribosomal subunit.

B Penicillin inhibits the transpeptidase that cross-links peptidoglycan peptides. Other antibiotics may target ribosomal subunits.

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?Choose one: A. polyunsaturated fatty acids B. saturated fatty acids C. unsaturated fatty acids D. ether-linked terpenoids E. cholesterol

B 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).

The major factor limiting bacterial growth in nature is Choose one: A. space. B. nutrients. C. antibacterial agents. D. temperature extremes. E. oxygen.

B The ability to find and acquire sufficient nutrients for growth is the major challenge faced by microorganisms.

Choose the pair of words that correctly completes the following sentence: Biofilms preferentially form in __________ environments with __________ levels of nutrients. Choose one: A. dry / high B. moist / high C. moist / low D. dry / low

B The ability to form biofilms allows bacteria to remain in places with good nutrient availability. Virtually any submerged or moist surface can encourage their formation (such as a rock in a stream, your teeth, or your dog's water bowl after a few days!).

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

B The cell membrane has many functions but protein production is not one of them. Ribosomes are responsible for the production of proteins.

Organisms that need to ingest reduced carbon are called Choose one: A. autotrophs. B. heterotrophs. C. lithotrophs. D. phototrophs.

B While autotrophs are self-feeding (meaning they assimilate CO2 as a carbon source, reducing it to make cell constituents), heterotrophs need to ingest reduced carbon. Lithotrophs generate ATP from reduced inorganic compounds, and phototrophs generate ATP using light. Lithotrophs and phototrophs may be either autotrophs or heterotrophs.

Which portion of LPS is most responsible for its toxic effects? Choose one: A. fatty acids B. lipid A C. disaccharide diphosphate D. O-antigen polysaccharide E. core polysaccharide

B You can see this becomes a problem when attempting to use antibiotics to treat severe infections caused by Gram-negative bacteria.

The dilution streaking technique can take a bit of practice to master. Which of the following represent sources of error that would likely result in failure to obtain isolated colonies? Choose one or more: A.forgetting to sterilize the loop prior to obtaining the inoculum B. flaming the loop immediately after obtaining the bacterial sample C. forgetting to flame the loop before streaking sequential sections of the plate D. allowing the loop to cool for too long before proceeding E.not creating a small section of overlap across sequential sections

B, C, & E It is important to remember to flame your loop between sections and allow it to cool sufficiently before contacting the cells again. Also, a small amount of overlap between sequential sections is necessary if the cells are to be "diluted" onto a fresh secton of agar. Finally, always remember to incubate your plate at the appropriate temperature for the cells to grow into colonies.

Which of the following statements are true regarding the early stages of biofilm formation? Choose one or more: A. Cells at this stage are very resistant to antibiotics. B. Cells may initially explore the substrate via twitching motility. C. Initial attachment involves cell surface structures (such as flagella, fimbriae, pili, and LPS). D. It requires communication between two or more bacterial species. E. Early colonists coat the surface with glycoproteins to recruit more cells. F. Environmental cues, such as pH and temperature, signal planktonic cells to settle.

B, C, E, & F Biofilms can be single species, and communication only occurs after microcolonies have formed. Cell surface structures such flagella, pili, fimbriae, and even LPS may function in initial attachment. Enhanced resistance to antibiotics develops later as the cells become encased in the matrix.

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

C 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.

Active transport is required for bacterial cells to Choose one: A. bring any charged molecule into the cell. B. move large polar solutes along their concentration gradient. C. transport solutes against their concentration gradient. D. move to environments with a higher nutrient concentration. E. exchange oxygen and carbon dioxide with the environment.

C Energy is required to move any molecule against its concentration gradient. Because the concentration of solutes is typically lower outside the cell relative to the cytoplasm, active transport represents an essential process for bacterial nutrition.

Recall from the introductory chapter how Louis Pasteur provided compelling evidence against the theory of spontaneous generation using his famous swan-necked flasks. But consider how the results might have been different if Pasteur had used a sample of soil containing Bacillus endospores! In fact, John Tyndall was unable to replicate Pasteur's experiments using hay infusion (containing spores). Further, before the current method of steam sterilization was introduced, Tyndall found a way to destroy them. John Tyndall discovered that intermittent boiling (cycles of heating and cooling) can kill bacterial endospores. This is a result of Choose one: A. accelerated degradation of the endospore cortex. B. cellular autolysins that are activated and degrade the endospore cell wall. C. endospores germinating into vegetative cells during the cooling phase. D. generation of toxic oxygen species that penetrate and kill the endospore. E. eventual depletion of nutrients in the treated medium.

C In the presence of sufficient nutrients, endospore germination would produce growing (vegetative) cells during the cooling phase. And if the solution were to be reheated at this point, it would kill the vegetative cells. By keeping the time between subsequent heating and cooling phases shorter than the amount of time required to form endospores, the solution become sterile (free of any living cells and/or endospores).

A complex medium is one that Choose one: A. is designed to specifically inhibit the growth of either Gram-negative or Gram-positive cells. B. contains specified amounts of five to ten known chemical components. C. is nutrient-rich, but the amounts and identity of specific nutrients are unknown. D. distinguishes among microorganisms based on some enzymatic or metabolic ability. E. is difficult and time consuming to make.

C Ingredients in complex media may include digests of yeast cells, animal proteins or tissues, and so on.

While adding nutrients to a culture medium in a glass container, which of the following would LEAST likely need to be added?Choose one: A. Nitrogen B. Magnesium C. Zinc D. Phosphorous

C Magnesium, nitrogen, and phosphorous are all macronutrients and would be needed in larger quantities than the micronutrient zinc.

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?Choose one: A. osmoregulatory proteins B. outer membrane lipoprotein C. lipopolysaccharide D. outer membrane porins E. capsular oligosaccharide

C The O-antigen polysaccharide is connected to the lipid A in LPS 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.

Consider a typical growth curve of a bacterial batch culture grown in the laboratory. Which of the following phases would be shortened, or absent entirely, if the culture was started using an inoculum from a log-phase culture (in the same medium)? Choose one: A. log phase B. stationary phase C. lag phase D. death phase

C The lag phase occurs when the cells in an inoculum gear up for growth in a new medium. Also, inocula taken from older cultures or agar plates usually contain a lot of dead or dormant cells. This phase would therefore be absent if an actively growing population of cells was transferred to a fresh medium of the same composition. Now consider what would happen if the new medium had a different carbon source.

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

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

If an organism has a mean growth rate constant (k) of 1/hour, then the mean generation time, g, is Choose one: A. 30 minutes. B. 120 minutes. C. 60 minutes. D. impossible to determine.

C The number of generations per hour, k, is the reciprocal of g.

The dilution streaking technique is probably the most common procedure performed by microbiologists on a daily basis. It is not, however, particularly useful for Choose one: A. isolating colonies from a mixed culture containing different bacterial species. B. transferring bacteria from a petri plate (as opposed to liquid culture as shown in the video). C. calculating the concentration of viable cells in a culture. D. culturing bacteria that stick together or grow as chains or clusters (such as Streptococcus and Staphylococcus).

C This technique is not quantitative.

Which of the following would not be included in the formulation of a defined medium? Choose one: A. potassium phosphate B. glucose C. tryptone D. magnesium sulfate E. sodium chloride

C Tryptone is a pancreatic digest of milk proteins. It provides a good source of amino acids and peptides for bacterial growth. The exact composition is unknown.

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. Choose one: A. CH3COOH, protonated B. CH3COO-, deprotonated C. CH3COOH, deprotonated D. CH3COO-, protonated

C Vinegar is about 5%-20% acetic acid, which in its uncharged form (CH3COOH) diffuses across lipid bilayers. It becomes deprotonated on the other side of the membrane, thus lowering the intracellular pH and causing acid stress. Vinegar has been used as a food preservative (e.g., in pickling) for thousands of years.

Which of the following is true of the newly synthesized daughter chromosomes? Choose one: A. One consists of a double helix of two new DNA strands, whereas the other is entirely parental. B. They remain single-stranded until after septation. C. Each chromosome contains one parental and one newly synthesized DNA strand. D. Each strand on each chromosome contains interspersed segments of new and parental DNA. E. They are both double-stranded, but nonidentical, because of crossing over.

C Just as in eukaryotes, DNA replication in prokaryotes is semiconservative.

The composition and health effects of the human microbiome are currently topics of extensive interest and research. For example, it is becoming increasingly apparent that the initial development of a robust intestinal microflora is dependent on many factors in a newborn's life, beginning with the mode of delivery (vaginal vs. cesarean section). Other potential influences include premature birth, exposure to antibiotics, and even mode of feeding. Suppose you were interested in the effect of breastfeeding versus formula feeding on the composition of gut flora in newborns. As part of your experiment, stool samples from healthy babies in the study get plated on various agar media. You notice that greater numbers of colonies are recovered when samples are plated on blood agar compared to Luria Bertani (LB) agar. After some diligent subculturing, you isolate several bacterial species capable of slow growth on the blood but not on the LB agar. You correctly surmise that these organisms Choose one: A. should be classified as beta-hemolytic. B. are Gram-positive and, thus, inhibited by the ingredients in LB agar. C. are opportunistic blood pathogens. D. have extensive and complex nutritional requirements not met by LB agar. E. grow because the blood agar suppresses the growth of faster-growing bacteria.

D Blood agar is an example of an enriched medium and is useful for cultivating certain bacteria (especially those that have become dependent upon a host organism) that are unable to grow on a regular complex medium such as LB.

Part 2: Which of the following early events in biofilm formation by Pseudomonas aeruginosa involves the extension and retraction of a specific pilus? Choose one: A. tethering adjacent cells together B. extracellular matrix production C. quorum sensing D. twitching motility E. genetic exchange between cells

D Cells of Pseudomonas aeruginosa lose their flagella early in the process of biofilm formation. Instead they translocate across the surface with the aid of specialized (type IV) pili.

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

D The lipopolysaccharides are only found in the outer membrane of Gram-negative bacteria.

Why are elements such as cobalt, copper, manganese, molybdenum, nickel, and zinc referred to as micronutrients? Choose one: A. They are required by microscopic organisms but not by most macroscopic organisms. B. If present, these will enhance growth, but they are not required. C. Care must be taken to add each of these elements to bacterial growth media. D. All cells require these elements in trace amounts. E. Their atomic numbers are lesser than those of most other nutrients.

D Yes, these elements are required by all cells, but they needn't be added to culture formulations; sufficient levels are found in the water and glassware used to prepare media.

Order the following events as they occur from beginning to end during DNA replication in a dividing cell. - Replisomes synthesize daughter chromosomes bidirectionally - Terminator site is replicated - DNA at origin unzips, and two replication forms form - Daughter cells separate - Septum forms

DNA at origin unzips, and two replication forms form Replisomes synthesize duaghter chromosomes bidirectionally Terminator site is replicated Septum forms Daughter cells separate In addition, remember that unlike eukaryotes, prokaryotes can carry out transcription and translation at the same time that their DNA is being replicated. This is one reason why bacteria can grow so fast.

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.

The FtzZ protein, found in both coccoid and rod-shaped bacteria, is important for maintaining the cell's ______ - turgor pressure - diameter - virulence - polarity - H+ gradient

Diameter FtsZ also plays a crucial role in cell division. In fact, it was originally identified because mutants in this gene exhibit a "filamentous temperature-sensitive" phenotype.

Which of the following features related to chromosomes and gene expression are characteristic of eukaryotes and/or prokaryotes? (Rare exceptions may occur.) - Haploid - Diploid - DNA replication and gene expressions are separated - Nucleoid - DNA is genetic material - DNA replication and gene expression can occur simultaneously - Nucleus with nuclear membrane - Ribosomes translate mRNA into protein

EUK: Nucleus with nuclear membrane, diploid, DNA replication and gene expression are separated PRO: Haploid, nucleoid, DNA replication and gene expressions can occur simultaneously BOTH: DNA is genetic material, ribosomes translate mRNA into protein All living cells contain DNA as their genetic material. With few exceptions, the prokaryotic genome consists of a single circular chromosome (so they are haploid), which is centrally condensed in a region known as the nucleoid. In contrast, eukaryotes are typically diploid and confine their multiple chromosomes in a membrane-bound nucleus. In all domains of life, the process of gene expression involves production of RNA transcripts and translation of the messenger RNA into protein by ribosomes. In prokaryotes, these processes can occur simultaneously with DNA replication, whereas eukaryotes spatially and temporally separate replication from gene expression.

The diameter of bacterial cells is controlled by the 1 _____ protein

FtsZ This protein, which is homologous to eukaryotic tubulin, is also required for formation of the septum during binary division. In fact, it was discovered and named after a strain of E. coli (Filamenting temperature-sensitive mutant Z) that did not divide normally because of a deficiency in this protein.

Part 1: Pseudomonas aeruginosa represents a well-studied model organism for single-species biofilm formation. This research is also of direct medical significance because of the propensity of these bacteria to form biofilms in the _________ of patients with cystic fibrosis. - Stomach - Nasal passages - Intestines - Lungs - Esophagus

Lungs Unfortunately, patients with cystic fibrosis are prone to lung infections by Pseudomonas aeruginosa. The biofilms are persistent and, over a period of time, produce significant damage.

All of the following organisms can cause some form of pneumonia or walking pneumonia. Some of them are vulnerable to the antibiotic penicillin. Imagine you are conducting an experiment to see which will survive in the presence of penicillin. Choose the graph below that best matches your predicted results. The organisms used in the experiment include the following: 1) the firmicute Streptococcus pneumoniae, 2) the proteobacterium Escherichia coli, 3) the fungus Candida albicans, and 4) Mycoplasma pneumoniae, a bacterium with no cell wall.

Only the Gram-positive and Gram-negative organisms have peptidoglycan cell walls.

Many biofilm-specific phenotypes are controlled by "quorum sensing." This system allows bacteria to regulate gene expression according to the concentration of _______ in its immediate environment. - Antibiotics - Oxygen - Phagocytes - Other bacteria - Nutrients

Other bacteria After the formation of microcolonies, signal molecules, which are normally constitutively produced by the bacteria, accumulate and stimulate transcription of genes required for development of the mature biofilm (matrix production, towers and channels, physiological resistance to antibiotics, and so on).

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.

Part 1: The Hawaiian bobtail squid Euprymna scolopes harbors a dense population of symbiotic, bioluminescent Vibrio fischeri in specialized light organs. An adult squid contains about 5 × 108 symbionts, and the light they produce provides counterillumination to help the squid avoid predation at night when it is foraging above the sand flats. The squid returns to the sand by daybreak, and at this time 95% of the symbiont population is expelled back into the environment. Assuming the remaining bacteria divide at a constant rate of growth, how many generations must take place to repopulate the organ by nightfall (12 hours later)? ______ generations Part 2: Based on your answer to Part 1, do you think the bacteria are dividing rapidly during the daytime? Find out by calculating the generation (doubling) time and enter it here: ______ minutes

Part 1: 4.3 Part 2: 167

Part 1: Label the four phases of the bacterial growth curve pictured here by dragging the labels to the correct targets. - Stationary phase - Lag phase - Death phase - Log phase Part 2: Suppose the researcher who ran this experiment also measured growth of the culture by taking optical density readings using a spectrophotometer. During which phase would the data be least proportional to that in the above graph (obtained using numbers of viable cells)? Choose one: A. log phase B. death phase C. lag phase D. stationary phase

Part 1: lag, log, stationary, death Just remember, this type of curve is only characteristic of bacteria growing in closed systems (such as a culture flask). Part 2: B Because dead cells still scatter light, the actual loss of viable cells would decrease at a faster rate than the turbidity.

For which organisms would this type of membrane lipid be most adaptive? (Isoprene cyclized to cyclopentane) Choose one: A. Mycobacterium tuberculosis in human lung tissues B. Archaea living in sea ice C. Archaea in a volcanic hot spring D. Bacteria in acidic mine run-off E. E. coli cells that are starved for nutrients

The the ability of archaeal membrane lipids to form monolayers by linking the tails of two terpenoid chains together, along with the presence of cyclopentane rings confers enhanced stability in extremely hot environments such as volcanic hot springs and hydrothermal vents

Part 1: Which of the following are characteristic of a vegetative cell, endospore, or both? - Uses central septation site - Small acid soluble proteins (SASPs) - Chromosome - Transcriptionally active - Binary division - Dipicolonic acid - Double membrane - Proteins - Peptidoglycan - Resistant to heat, UV light, desiccation, etc. - Metabolically active - Ribosomes

Vegetative cell - Metabolically active - Transcriptionally active - Uses central septation site - Binary division Endospore - Small acid soluble proteins (SASPs) - Resistant to heat, UV light, desiccation, etc. - Dipicolinic acid - Double membrane Both - Peptidoglycan - Chromosome - Proteins - Ribosome The unique structure, chemical composition, and metabolic inactivity of the endospore allow it to survive conditions that would kill vegetatively growing cells.

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. - Inorganic ions - Nucleic acid (DNA + RNA) - Lipids - Protein - Water

Water > Protein > Nucleic acid > Lipids > Inorganic ions Realize, however, that the order would be slightly different if we were to rank solely on the basis of number of molecules per cell. Water would still be most abundant (20 billion molecules per cell), but at roughly 250 million total, the number of inorganic ions (e.g., protons, potassium, magnesium, and phosphate) outnumbers lipids by 10:1, proteins by 100:1, and total nucleic acids by 1000:1!