Microbiology Chapter 3 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.
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.
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.
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 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 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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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!
