Microbio Ch. 3

Order the following events as they occur from beginning to end during DNA replication in a dividing cell.

1. DNA at origin unzips and two replication forks form 2. Replisomes synthesize daughter chromosomes bidirectionally 3. Terminator site is replicated 4. Septum forms 5. 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.

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.

1. Water 2. Protein 3. Nucleic acid (DNA + RNA) 4. Lipids 5. 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!

The following illustration depicts a cell that is synthesizing membrane transporters. Correctly label each of the targets with the corresponding item on the right. Ribosome DNA-binding protein Nascent membrane protein RNA Signal recognition particle (SRP) DNA Origin of replication Which key enzyme directly involved in the above process is not explicitly shown in the illustration? A. DNA polymerase B. sortase C. transpeptidase D. RNA polymerase E. ATP synthase

A) Ribosome E) Signal recognition particle (SRP) C) Nascent membrane protein D) RNA B) DNA-binding protein G) Origin of Replication F) Signal recognition particle (SRP) RNA polymerase In addition to coupling transcription and translation, bacteria can simultaneously traffic proteins using signal recognition particles (SRPs). These RNA-polypeptide complexes bind to N-terminal sequences on nascent membrane proteins (and those destined for the periplasm or secretion). The act to direct the proteins to their intended destinations as well as to prevent premature folding of the nascent polypeptide. Just as many ribosomes can cotranslate a given transcript, so can multiple RNA polymerases transcribe the same gene, one following behind the other.

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

A. It provides protection from osmotic rupture. C. It is also known as the cell wall. D. It is composed of peptidoglycan. 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).

Penicillin (directly or indirectly) targets which of the following? Choose one or more: A. cell wall synthesis B. cross-linking of peptidoglycan peptides C. biosynthesis of the cell membrane D. porin assembly E. biosynthesis of lipopolysaccharides F. transpeptidase activity

A. cell wall synthesis B. cross-linking of peptidoglycan peptides F. transpeptidase activity Penicllin targets the formation of peptide bonds in the peptidoglycan cell wall by attaching to the transpeptidase enzyme and preventing it from forming peptide cross-links.

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

A. glycogen C. elemental sulfur (S0) E. polyhydroxybutyrate (PHB) 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 cell components listed below are characteristic of all bacteria, and which are specialized structures found in only some bacteria?

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.

Which of the following organisms have peptidoglycan? A. an archaeon such as Methanococcus jannaschii B. Bacillus subtilis C. an amoeba D. Pseudomonas aeruginosa

B. Bacillus subtilis D. Pseudomonas aeruginosa Peptidoglycan is a distinguishing trait in bacteria. Archaea sometimes have an analogous cell wall made of pseudo-peptidoglycan. However, eukaryotes do not have peptidoglycan.

Examine and correctly label the various portions of bacterial lipopolysaccharide as shown here. O-antigen polysaccharide Core polysaccharide Disaccharide diphosphate Lipid AFatty acids

Because LPS has potent immunostimulatory effects, it is also known as endotoxin.

Why do bacteria usually contain an even number of replisomes? A. There are two copies of the gene that codes for DNA polymerase, an important enzymatic protein component of replisomes. 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. Because replication is bidirectional, there are two replication forks emanating from the origin of replication.

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.

Select the option from the list that contains the missing words from the following sentences. 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. A. CH3COOH, deprotonated B. CH3COO-, protonated C. CH3COOH, protonated D. CH3COO-, deprotonated

CH3COOH, deprotonated 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.

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. a) RNA b) DNA c) biosynthetic precursors d) LPS a) phospholipid b) peptidoglycan c) polyamine d) periplasm

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

Each chromosome contains one parental and one newly synthesized DNA strand. Just as in eukaryotes, DNA replication in prokaryotes is semiconservative.

Which of the following features related to chromosomes and gene expression are characteristic of eukaryotes and/or prokaryotes? (Rare exceptions may occur.)

Eukaryotes -Nucleus with nuclear membrane -Diploid -DNA replication and gene expression are separated Prokaryotes -Haploid -Nucleoid -DNA replication and gene expression can occur simultaneously Both -DNA is genetic material -Ribosomes translate mRNA into proteins Prokaryotes can even begin a subsequent round of DNA replication before a current one has been completed. Would this be possible for a eukaryotic cell?

The diameter of bacterial cells is controlled by the __________ protein a) OmpF b) MreB c) CreS d) RodZ e) FtsZ

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.

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.

Graph A Streptococcus pneumoniae & Escherichia coli die after adding penicillin while Candida albicans, and Mycoplasma pneumoniae survive Only the Gram-positive and Gram-negative organisms have peptidoglycan cell walls.

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

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

Examine the following illustrations of a Gram-negative and Gram-positive cell envelope and place the labels on the correct targets. Inner membrane Lipoprotein LPS Cell membrane Periplasm Membrane proteins Teichoic acids Outer membrane S-layer Peptidoglycan Glycosyl chains Porin

Most cultured bacteria can be described as either Gram-positive or Gram-negative on the basis of their cell wall structure and corresponding appearance in the Gram stain. However, differences in the cell walls of other bacteria and archaea render them difficult to distinguish by this staining method. One example is "acid-fast" bacteria such as Mycobacterium spp., which have high concentrations of waxy lipids in their cell envelopes.

Certain aquatic bacteria use magnetosomes to direct them to environments with optimal levels of a) oxygen b) iron c) pH d) CO2 e) nutrients

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.

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

Production of proteins The cell membrane has many functions but protein production is not one of them. Ribosomes are responsible for the production of 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? A. unsaturated fatty acids B. ether-linked terpenoids C. cholesterol D. polyunsaturated fatty acids E. saturated fatty acids

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).

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

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

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

A new antibiotic has been created to target bacterial peptidoglycan in the cell wall. It is a small antibiotic that can fit in porins and can can thus get past the outer membrane of Gram-negative organisms. Which of the following would NOT be targeted by this new antibiotic? Choose one: A. a Gram-positive such as Clostridium difficile B. a Gram-negative such as Pseudomonas aeruginosa C. a bacterium with no cell wall such as species of the genus Mycobacterium D. Escherichia coli

a bacterium with no cell wall such as species of the genus Since this new antibiotic targets the cell wall, it will only impact organisms with a cell wall such as the two Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa and the Gram-positive Clostridium difficile. Without a peptidoglycan cell wall, Mycoplasma species will not be impacted by this new antibiotic.

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

a cyanobacterium 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.

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

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.

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 a) ABC transporters b) antiporters c) hopanoids d) aquaporins e) aquachelins

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.

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

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.

For which organisms would this type of membrane lipid be most adaptive?

archaea in a volcanic hot spring 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.

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

cell wall cross-link formation. Penicillin inhibits the transpeptidase that cross-links peptidoglycan peptides. Other antibiotics may target ribosomal subunits.

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

coccoid-shaped 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.

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

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

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

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

lipopolysaccharide 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.

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

mycolic acids 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).

Movement of molecular oxygen (O2) and carbon dioxide (CO2) across the cell membrane 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. occurs passively, but membrane transporters are required to facilitate their movement. E. only occurs when the O and C atoms are part of some other molecule (e.g., a sugar or amino acid).

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.

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

osmotic lysis 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 lipopolysaccharides are found in the A. periplasm. B. inner membrane. C. cytoplasm. D. outer membrane.

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

What type of enzyme in the replisome catalyzes addition of nucleotides to the growing DNA strands? A. polymerase B. helicase C. gyrase D. recombinase E. transcriptase Regarding the enzyme in Part 2, twelve of these would be required if a new round of DNA replication began before the first one terminated.

polymerase 12 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. The ability of prokaryotes to produce multiple replication forks permits generation times much faster than those required to actually replicate the DNA.

Septum

the new cell wall that forms between two daughter cells as a result of cell division

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

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

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

transport solutes against their concentration gradient. 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.