Microbio Exam 2
differentiate bacteriostatic agents from bactericidal agents. Provide examples of bacteriostatic and bactericidal antimicrobial measures
bacteriostatic: slow or stop metabolism or reproduction, but are not necessarily lethal; inhibit bacterial growth bactericidal: lethal effects; kill bacteria
compare and contrast boiling, autoclaving, and pasteurization. Explain how moist heat compares to dry heat methods
boiling: kills vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses within 10 minutes at sea level; boiling time is the critical factor; temperature cannot exceed 100C at sea level; steam carries some heat away; water boils at lower temperatures at higher elevations; requires longer boiling time; endospores, protozoan cysts, and some viruses can survive boiling autoclaving: pressure applied to boiling water prevents steam from escaping; boiling temperature increases as pressure increases; 121C, 15psi, 15-20 minutes pasteurization: heat treatment invented by Pasteur in 1864 to kill bacteria that cause spoilage in fermenting beer and wine, without affecting the texture, color, or taste; not sterilization: heat-tolerant microbes survive; these do not cause spoilage prior to consumption, generally not pathogenic moist heat: more effective than dry heat because water is a better conductor of heat than air dry heat: used for materials that cannot be sterilized with moist heat; denatures proteins and oxidizes metabolic and structural chemicals; requires higher temperatures for longer time than moist heat; incineration is ultimate means of sterilization
compare and contrast broad-spectrum antibiotics and narrow-spectrum antibiotics, including when it is most appropriate to use each type
broad spectrum: effective against many organisms; may allow for secondary or superinfections to develop, killing of normal flora reduces microbial antagonism narrow-spectrum: effective against few organisms; use when you know what the infection is
Describe how AZT and HAART treatment impact HIV's lifecycle
-AZT is a nucleoside reverse transcriptase inhibitor (base analog that halts elongation); reverse transcriptase has an extremely high mutation rate, so HIV quickly becomes resistant to AZT monotherapy -HAART: Highly Active Antiretroviral Therapy; drugs inhibit multiple steps; triple combination or cocktail therapy; more difficult for HIV to become simultaneously resistant to 3 drugs 1. fusion/entry inhibitors 2. reverse transcriptase inhibitors 3. integrase inhibitors 4. protease inhibitors -severe side effects in some patients: diabetes, pancreatitis, lipodystrophy, lactic acidosis, diarrhea -drug resistant HIV strains -expensive and requires complicated medical care. NOT a cure. Life-long therapy required. Viral levels quickly rebound if therapy is stopped
describe the form and motility of ameba, and provide examples of diseases caused by the ameba
-Amebas move using pseudopods. Loped amebas have large, lobular pseudopods, whereas filamentous amebas have needle-shaped pseudopods. -Entamoeba histolytica: causes intestinal amebiasis. The amebas develop into cysts that are expelled in feces and remain dormant for long periods in water -Naegleria fowleria: causes meningoencephalitis, an infection of the brain; enter through nose while swimming -Acanthamoeba: infects the keratin layers of the cornea (keratitis), wwhich becomes inflamed and clouded. Commonly results from improperly cleaned contact lenses.
provide examples of antibiotics that target protein synthesis
-Aminoglycosides (streptomycin): affects aerobic bacteria (Gram-positive and Gram-negative) via 30S subunit: binds 16S rRNA at A site; interfere with incoming aminoacly-tRNA. Also affects envelope stability -Tetracyclines: affects bacteria via 30S subunit: blocks incoming aminoacyl-tRNA from binding A site. -Macrolides(erythomycin): affects bacteria via 50S subunit: Binds peptide release tunnel and blocks translocation from A site to P site -Oxazolidinones(linezolid): affects gram-positive bacteria via 50S subunit: binds 23S rRNA near P site; inhibits translation
explain the steps of replication by DNA polymerase, including initiation, elongation, and termination
-Bacterial DNA replication begins at the origin and is bidirectional -DNA polymerase III adds nucleotides to hydroxyl group at 3' end of nucleic acid; replicates DNA in 5' to 3' direction -because strands are antiparallel, new strands are synthesized differently; leading strand synthesized continuously, lagging strang synthesized discontinuously -replication ends at the terminus as DNA polymerase I fills in the gaps to create a continuous DNA molecule
explain the steps necessary to engineer a human gene into a bacterial plasmid
-Bacterial plasmids can be engineered to express human genes -insert a eukaryotic DNA sequence for a product of interest into a plasmid (introns must be removed) -insert a piece of DNA into a plasmid or viral DNA cut with the same restriction enzyme. -the DNA backbone is sealed with DNA ligase -the inserted piece of DNA has a gene that can be expressed by a cell containing the recombinant plasmid or infected by a recombinant virus
explain why fungi may perform both asexual and sexual reproduction, using the life cycle of the ascomycete fungi Aspergillus as an example
-Filamentous fungi can expand at great length by asexual division (mitosis) -eventually they run out of nutrients, and the cells undergo meiosis to form gametes -the gametes develop into spores for dispersal -in Aspergillus, the tips of the diploid mycelium undergo meiosis and develop into haploid ascospores within a pod called an ascus -the ascospores disperse until they germinate in a region of fresh resources -each ascus undergoes cell divisions to form a haploid mycelium, which is male or female -the male and female structures fuse, followed by migration of all the male nuclei into the female structure -the paired nuclei then undergo several rounds of mitotic division while migrating into the growing mycelium -in the mycelial tips, the paired nuclei finally fuse (becoming 2n) and re-form a diploid mycelium -overall, the diploid-haploid life cycle enables a fungus to respond genetically to environmental change by reassorting its genes through meiosis and by recombining them through fertilization -gene reassortment and recombination provide new genotypes, some of which may increase survival in the changed environment
describe the major capsid morphologies and explain the importance of a capsid
-Helical capsid: usually formed from one protein that interlocks to form a helix-like structure around the viral genome. Can vary in length to accommodate different lengths of nucleic acid. -Icosahedral: radial symmetry; a polyhedron with 200 identical triangular faces. Often formed by either one to three repeating subunits of capsid proteins -Complex: icosahedral head + helical tail; think bacteriophage; not found in plant of animal viruses
describe the ribosomal steps of initiation, elongation, and termination during translation
-Initiation: occurs wwhen the 30s subunit binds mRNA. The formylmethionyl-tRNA binds to an AUG codon of the first gene in the mRNA. Binding of the 50S site completes initiation -Elongation: comprises aminoacyl-tRNA entry and peptide bond formation. Each new aminoacyl-tRNA binds the A site, with anticodon-codon pairing. If the pairing is correct, the 50S subunit catalyzes peptide bond formation. The mRNA translocates one position, so that now the "new" tRNA (holding onto the growing peptide) occupies the P site -Termination: occurs when a stop codon in the mRNA enters the A site. The completed peptide is released, and the 30S and 50S ribosomal subunits fall off, to commence translation elsewhere.
define phytoplankton and explain the role of algae in the environment
-Major photosynthetic producers are the algae; in aquatic and marine ecology, the algae, together with photosynthetic bacteria, are known as phytoplankton -they fix most of Earth's carbon and produce most of the oxygen we breathe
explain the different kinds of mutations and how they occur
-Missense Point Mutation: single nucleotide is changed in a DNA sequence, leading to the expression of an altered protein -Nonsense Point mutation: single nucleotide is changed in a DNA sequence, replacing an amino acid codon with a codon that specifies no amino acid and terminates translation -Insertion Frameshift - addition of one or more nucleotides that shifts the reading frame of the codons -Deletion Frameshift - removal of one or more nucleotides that shifts the reading frame of the codons
list the major cellular processes targeted by antibiotics and provide examples of antibiotics for each category
-Peptidoglycan synthesis (cell wall inhibitors) - penicillins, cephalosporins, vancomycin, bacitracin, monobactams; (cell membrane inhibitors) - polymyxins -metabolic inhibitors - sulfonamides, trimethoprim -DNA replication inhibitors - quinolones -RNA Polymerase Inhibitors - Rifampin, Pyronins -Protein Synthesis inhibitors (50S ribosome subunit) - Chloramphenicol, Macrolides, Clindamycin, Oxazolidinones, Streptogramins (30S ribosome subunit) - Aminoglycosides, Tetracyclines
describe the steps involved in PCR, and provide examples of beneficial applications of PCR
-Place the DNA to be copied in a tube -Add DNA primers (oligonucleotides) that have complementary sequences to the sequences on either side of the region of DNA to be copied (e.g. on either side of a gene) -Add Taq polymerase (A DNA polymerase that won't denature at high temperatures; isolated from the hyperthermophile Thermophilus aquaticus) -Program the thermocycler to repeat the following steps 20-40 times: 1. denaturation: heat to 95C to separate the DNA strands (break hydrogen bonds between nucleotides) 2. annealing: cool to 55C so the primers hybridize to the complementary sequence on the DNA 3. Extension/elongation: heat to 72C for the optimal Taq polymerase replication of the DNA, resulting in exponential replication of the DNA region of interest. -viral/bacterial burden below detectable levels -presence of antibiotic resistance genes -microbial population analysis -amplification of DNA at a crime scene -genetic screening
describe the different kinds and functions of RNA products that are made from DNA
-RNA primers: needed for DNA replication -Messenger RNA: encodes genes for translation into proteins -Ribosomal RNA: translational machinery -Transfer RNA: carry amino acids to the ribosome
explain the function of a viral envelope, including how the envelope helps mediate entrance and exist from the host cell
-a viral envelope can help the virus avoid the host's immune system and ease fusion with the host plasma membrane -acquired from host cell during viral replication or release (envelope consists, in part, of the host membrane) -composed of phospholipid bilayer and proteins (some proteins are virally-encoded glycoproteins (spikes)) -envelope proteins and glycoproteins often play role in host recognition
distinguish between a trophozoite and a cyst
-amebas are usually ingested in the form of cycts, dormant cells encased in a tough coating (resting stage for unfavorable conditions) -once they reach favorable conditions, they can excyst and devlop into trophozoites, amebas with pseudopods that phagocytose prey (active feeding stage)
outline the complex life cycle of Plasmodium falciparum, the parasite that causes malaria
-caused by apicomplexan parasites Plasmodium falciparum and P. vivax -carried by mosquitoes, which transmit the parasite to humans when the insect's proboscis penetrates the skin -transmitted parasites invade the liver, where they develop into the "merozoite" form, which invades red blood cells -the merozoite first contacts a red blood cell through interaction between its apical complex (the structure at the penetrating tip of the cell) and receptor proteins on the red blood cell -the apical complex contains a pair of secretory organelles that are capped by a ring of microtubules and that inject enzymes that facilitate invasion. -eventually, the entire merozoite enters the host cell, leaving no traces of the parasite on the host cell surface -thus, the internalized parasite becomes invisible to the immune system until its progeny burst out -some progeny are then picked up by mosquitoes, where they undergo a sexual life cycle and are transmitted to new hosts
explain how egress differs for an enveloped virus compared to a naked virus
-enveloped viruses place viral proteins in the host cell plasma membrane, dock to them, and 'bud' out of the cell, taking a portion of the plasma membrane with them -naked viruses almost always exit by lysis of host cell
describe the steps involved in genetic sequencing, and provide examples of beneficial applications of genetic sequencing
-essentially uses PCR but wwith some fluorescently-labeled dideoxyribonucleotides (ddNTPs) -DNA polymerase can't build on ddNTP -end result: whenever one of the fluorescently tagged nucleotides is added, further elongation of that strand is stopped -the fragments can then be separated by length, with the fluorescent tag at the end of the fragment revealing which nucleotide occurs at that point -used to characterize microbial pathogens and track their evolution and spread -used to characterize which types of microbes are present in an environment, e.g. human microbiome project -identifies genetic polymorphisms associated with disease -forensic identification -paternity testing
describe how filtration controls microbial growth and give several examples of where filters are commonly found
-for heat-sensitive media or chemical additives -filtration through filter with a pore size of 0.2 nm removes bacteria and bacterial endospores, yeasts, mold spores, algae, and protozoa, but not viruses -to remove viruses, filters with pore sizes of 20nm are necessary (1nm = 000.1um) -HEPA filters are present in biosafety cabinets, in the air ducts of operating rooms, and in the rooms of highly contagious patients
explain what a dimorphic fungus is, and provide examples of dimorphic fungi important in human disease
-fungi that can exist in the form of both mold and yeast -Candida albicans: important member of human vaginal biota, but also an opportunistic pathogen, causing infections such as thrush in the mouth of patients with AIDS -Blastomyces dermatitidis: the cause of blastomycosis, a type of pneumonia; forms a mycelium in culture and in soil environments but grows as a yeast within the infected lung
describe how host range (tissue tropism) is determined, and compare and contrast a specialist to a generalist
-host range: the species or cell type that a virus can infect is usually very specific. The ability for a virus to infect a cell relies on the virus's ability to attach to the cell and gain entry inside the cell.; host range is dictated by the interaction between viral attachment proteins and host cell receptor molecules; host cell receptors are often molecules critical for cellular function -generalist: infects many kinds of cells in many different hosts
using the terms DNA replication, transformation, transcription, and translation, explain how a recombinant DNA plasmid expressing the insulin gene could produce human insulin
-isolate eukaryotic processed RNA containing the human insulin gene -convert the RNA into DNA using the HIV enzyme reverse transcriptase -insert eukaryotic DNA sequence for insulin into a plasmid -insert plasmid containing recombinant DNA into bacterial cell such as E. Coli via transformation -the E. coli cell will undergo DNA replication, transcription, and translation to produce numerous insulin products
describe the lytic and lysogenic replication cycle of bacteriophages
-lysis occurs when the phage genome reproduces progeny phage particles, as many as possible, and then lyses the cell to release them -lysogeny occurs when the phage genome integrates itself into that of the host. The phage genome is replicated along with that of the host cell. The phage DNA, however, can direct its own excision. This excised phage genome then initiates a lytic cycle
explain the concept of selective toxicity and how this relates to the relative availability of antibacterial drugs compared to antiviral or antifungal drugs
-more toxic to an infectious microbe than to the host/host cells -antibacterial drugs are the easiest to develop because the are the least similar to human cells
describe the structure of a bacterial genome, and explain how it differs from a eukaryotic genome
-most bacteria have a genome in the form of a circular chromosome containing several million base pairs; the information determining when a gene is expressed is contained in a DNA control sequence called a promoter. In bacteria, genes often exist in a series, in a unit called an operon. All genes in an operon are lined up head to tail on the chromosome, and their expression (RNA synthesis) is controlled by a single promoter located in front of the first gene. Bacterial genomes are packed with genes that encode proteins, with very little unused sequence between them; Bacteria may have additional smaller pieces of DNA called plasmids which may enter of leave a bacterial cell without changing the species -the human genome contains 95% noncoding sequences. The human coding genes are usually single, but they may be interrupted by noncoding introns. Eukaryotic genes are separated by large stretches of noncoding DNA
compare the mechanisms used by enveloped animal viruses, non-enveloped viruses, and bacteriophages to gain entry into host cells
-non-enveloped animal viruses: usually enter via receptor-mediated endocytosis 1. the virus attaches to the cell receptor 2. endocytosis is initiated 3. an endosome forms with the virus inside 4. the nucleocapsid escapes to the cytoplasm and uncoats to release the genome -enveloped viruses usually enter by fusing with the host cell's plasma membrane 1. the virus attaches to the cell receptor 2. a conformational change in the attachment protein and bound receptor initiates membrane fusion 3. the viral envelope fuses with plasma membrane 4. the nucleocapsis enters the cytoplasm and uncoats to release the genome -bacteriophages weaken the bacterial cell wall and then directly penetrate the plasma membrane to insert its viral genome 1. tail fibers attach to receptors 2. conformational change in tail fibers bring base of the tail in contact with host cell surface 3. rearrangement of tail proteins allows inner core tube proteins to extend down into cell wall 4. contact with the plasma membrane initiates transfer of DNA through a pore formed in the lipid bilayer
explain what a plasmid is and describe the role of plasmids in the spread of antibiotic resistance genes
-plasmids are small, circular molecules of non-essential DNA -can confer survival advantages: F plasmids carry genes for conjugation pilus construction, R plasmids carry genes for antibiotic resistance
describe how Tamiflu impacts influenza's lifecycle
-prevents influenza virus from leaving the cell by inhibiting neuraminidase, which leaves host receptor, releasing virion to bud out
describe the key cellular structures in algae, and distinguish among green, red, and brown algae
-protists that conduct photosynthesis by using chloroplasts which evolved from ingested cyanobacteria through the process of endosymbiosis -unicellular or multicellular -photosynthetic -simple reproductive structures -classification based on the basis of pigmentation, storage products, and composition of cell wall -do not infect humans Green algae (Chlorophyta): unicellular, share characteristics with plants; have chlorophylls a and b; use sugar and starch as food reserves Red algae (Rhodophyta): red accessory pigment phycoerythrin; use the storage molecule glycogen; cell walls composed of agar or carrageenan-both are used as thickening agents Brown algae (Phaeophyta): produce chlorophylls a and c, carotene, and xanthophylls; use laminarin and oils as food reserves; cell walls are composed of cellulose and alginic acid
contrast schizogony with the reproductive process conjugation in protozoa
-schizogony: asexual reproduction in some protozoa, occurs within red blood cells and liver cells; multiple mitoses form multinucleate Schizont; after cytokinesis results in uninucleate Merozoites -conjugation: sexual reproduction in some protozoa; two different mating types fuse, diploid micronuclei go through meiosis to produce haploid nuclei, and the cells exchange micronuclei
explain how RNA polymerase copies a sequence of DNA to form mRNA and explain the role of a sigma factor
-sigma factors bound to RNA polmerase core enzyme (only one type in bacteria) direct the combined holoenzyme to a promoter -different sigma factors can direct core RNA polymerase enzyme to different genes as needed -1 sigma factor can help activate multiple genes -once RNA polymerase is situated, the sigma factor dissociates and RNA polymerase begins transcribing RNA from ribonucleoside triphosphates (rNTPS)
describe how reproduction occurs in a yeast
-some yeasts are asexual, whereas others alternate between diploid (2n) and haploid (n) forms. Both haploid and diploid forms are single cells -the haploid (n) cells undergo several generations of mitosis and budding (vegetative growth) -at some point, various stress conditions, such as nutrient limitation, may lead the haploid cells to develop into gametes -the gametes are of two mating types -cells of the two mating types may fertilize each other by fusing together and combining their nuclei to make a diploid (2n) zygote -the diploid cell, like the haploid cell, may undergo vegetative budding and reproduction -under stress, however, a 2n cell may undergo meiosis, regenerating haploid cells -the haploid progeny possess chromosomes reassorted and recombined from those of their "parental" gametes
describe the structure of the fungal mycelium in filamentous fungi
-thallus - non-reproductive body -filamentous fungi form branching tufts called a mycelium -their tough cell walls are composed of chitin, consisting of polymers of N-acetylglucosamine (NAG) -NAG of chitin is target of antifungal agents (Nikkomycin Z) -grow by extending multinucleate cells called hyphae -as a hypha extends, its nuclei divide mitotically without cell division
describe the traits of trypanosomes, and provide examples of diseases caused by trypanosomes
-trypanosomes are obligate parasites with a single flagellum and large single mitrochondria. Trypanosome undergo complex life cycles. They cause sleeping sickness (Trypanosoma brucei), Chagas' disease (trypanosoma cruzi), and leishmaniasis (Leishmania donovani)
list the levels of gene regulation and explain why it is useful to regulate gene expression at different levels
1. Control of transcription - activators and repressors 2. Translational control - translation initiation sequences in the mRNA, which recognize specific translational repressor proteins 3. Posttranslational control - activity of proteins can be controlled by modifying their structure (protein cleavage, phosphorylation, methylation) microbes sense their environment and regulate gene expression to optimize growth and survival.
compare and contrast the categories of antimicrobial agents
1. Phenol and Phenolics: intermediate to low-level disinfectants; denature proteins and disrupt cell membranes; effective in presence of organic matter and remain active for prolonged time; commonly used in health care settings, labs, and homes (lysol, triclosan) 2. alcohols: intermediate-level disinfectants; denature proteins and disrupt cytoplasmic membranes; more effective than soap in removing bacteria from hands; swabbing skin with 70% alcohol prior to injection removes most microbes (but more by physical action (degerming) than be chemical action) - water helps penetrate membrane and slows down how fast it evaporations 3. Halogens: include iodine, chlorine, bromine, and fluorine; intermediate-level antibicrobial chemicals; damage proteins by denaturation; widely used in numerous applications, iodine tablets, iodophors, chlorine treatment, bleach, bromine disinfection, and the addition of fluoride to water and toothpastes (Betadine, an iodophor, slowly releases iodine) 4. Oxidizing agents: peroxides, ozone, and peracetic acid; kill by oxidation of microbial enzymes; high-level disinfectants and antiseptics; hydrogen peroxide can disinfect and sterilize surfaces (not useful in treating open wounds because of catalase activity); ozone treatment of drinking water; peracetic acid is effective sporicide used to sterilize equipment 5. surfactants: "surface active" chemicals, reduce surface tension of solvents; soaps and detergents, soaps have hydrophilic and hydrophobic ends, good degerming agents but not antimicrobial; detergents are positively charged organic surfactants, quaternary ammonium compounds (quats): low-level disinfectants that disrupt cellular membranes, ideal for many medical and industrial applications 6. heavy metals: heavy-metal ions denature proteins; low-level bacteriostatic and fungistatic agents; 1% silver nitrate once commonly used to prevent blindness caused by N. gonorrhoeae; thimerosal used to preserve vaccines; copper controls algal growth 7. Gaseous agents: microbicidal and sporicidal gases used in closed chambers to sterilize items, e.g. ethylene oxide; denature proteins and DNA by cross-linking functional groups; used in hospitals and dental offices: disadvantages: can be hazardous to people, often highly explosive, extremely poisonous, potentially carcinogenic 8. Enzymes: antimicrobial enzymes act against microorganisms,; human tears contain lysozyme, digests peptidoglycan cell wall of bacteria; uses of enzymes to control microbes in the environment: lysozyme is used to reduce the number of bacteria in cheese, prionzyme can remove prions on medical instruments
explain how disinfectants are compared
1. Use-dilution test: most effective agents entirely prevent growth at highest dilution; current standard test in the US -metal cylinders dipped into broth cultures of bacteria -contaminated cylinder immersed into dilution of disinfectant -cylinders removed, washed, and placed into tube of medium 2. In-use test: accurate determination of proper strength and application procedure for each specific situation -swabs taken from objects before and after application of disinfectant or antiseptic -swabs inoculated into growth medium and incubated -medium monitored for growth 3. Phenol coefficient: evaluates efficacy of disinfectants and antiseptics; compares to phenol an agent's ability to control microbes; greater than 1.0 indicates agent is more effective than phenol; has been replaced by newer methods
explain the basis of the Baltimore Classification system
1. genome type provides information about how a virus will generate mRNA and replicate its genome and gives you insight into its lifecycle even if you know nothing else about the virus
explain how antimicrobial resistance can be retarded
1. maintain high concentration of drug in patient for sufficient time (kills all sensitive cells and inhibits others so immune system can destroy resistant cells) 2. use antimicrobial agents in combination (synergism versus antagonism) 3. use antimicrobials only when necessary 4. develop new variations of existing drugs (second-generation drugs, third-generation drugs) 5. search for new antibiotics, semisynthetics, and synthetics (bacteriocins, design drugs complementary to the shape of microbial proteins to inhibit them)
describe the factors that dictate which route of administration is selected
1. toxicity: cause of many adverse reactions is poorly understood, drugs may be toxic to kidneys, livers, or nerves, consideration needed when prescribing drugs to pregnant women 2. allergies: allergic reactions are rare but may be life threatening, anaphylactic shock 3. Disruption of normal microbiota: may result in secondary infections, overgrowth of normal flora, causing superinfections, of greatest concern for hospitalized patients
compare and contrast how protozoa and algae acquire their nutrition
Algae: all algae are protists with chloroplasts that conduct photosynthesis. Green and red algae are autotrophic photosynthesizers; brown algae show "mixotrophic" nutrition, involving both photosynthesis and heterotrophy Protozoa: Chemoheterotrophic: obtain nutrients by phagocytizing bacteria, decaying organic matter, phagocytozing protozoa, and invading tissues of host; few absorb nutrients from surrounding water; dinoflagellates and euglenoids are photoautotrophic
describe the distinctive traits of ciliates, dinoflagellates, and apicomplexans
All alveolates: Cell form is highly structured. "alveolate" refers to the flattened vacuoles called alveoli within the outer cortex. ciliates: heterotrophic protists that consume algae and smaller protists and are in turn consumed by amebas. Consists of a single cell covered with large numbers of stubble-like cilia containing microtubules powered by ATP. Cilia serve functions in cell propulsion and food acquisition. The cell maintains to types of nuclei: the micronucleus, hose genes maintain genetic fidelity for sexual reproduction; and the macronucleus, containing multiple gene copies that express gene products throughout the large cell. During asexual reproduction, both micronuclear and macronuclear chromosomes undergo replication. For sexual reproduction, a ciliate undergoes conjucation. Dinoflagellates: major group of marine algae, essential to marine food chains. Blooms of red dinoflagellates cause the famous "red tide", release toxins that can be absorbed by shellfish, poisoning human consumers months or years later. Stiff alveolar plates on cortex, composed of proteins or calcified polysaccharides; possess just two long flagella, one of which wraps along a crevice encircling the cell; contain chloroplast and photosynthesize; also phagocytose prey Apicomplexans: form a major group of parasites of humans and other animals. Name derives from the "apical complex", a specialized structure that facilitates entry of the parasite into a host cell. Possess an elaboarate cortex composed of alveoli, pores, and microtubules; but as parasites, they have undergone extensive reductive evolution, losing their flagella and cilia; tubular mitochondria; chemoheterotrophs
describe the major mechanisms by which a bacterium achieves resistance against an antibiotic
Antibiotic resistance genes can be plasmid-borne or they can be part of the chromosome. A specific antibiotic resistance gene will carry out only one of the four: 1. modify the target so that it no longer binds the antibiotic 2. destroy the antibiotic before it gets into the cell 3. add modifying groups that inactivate the antibiotic 4.pump the antibiotic out of the cell using specific transport proteins (for example, tetracycline export) or non-specific transport proteins
describe the different classes of viral genomes, and give an example of each
Class I: dsDNA genome - Human herpesvirus Class II: ssDNA genome - Parvoviruses Class III: dsRNA genome - Reoviruses Class IV: ssRNA genome, positive sense - Poliovirus Class V: ssRNA genome, negative sense - Influenza viruses Class VI: ssRNA genome, DNA intermediate - HIV Class VII: dsDNA genome, RNA intermediate - Hepatitis B Virus
define decimal reduction time and explain how determining the D-value helps in complete sterilization
D-value: time required to kill 90% of the cells, i.e. time required for viable cell count to drop by one log10 unit the longer you wait, the more that will die
define recombinant DNA
DNA produced by combining DNA from different sources
describe the tests used to measure antimicrobial drug efficacy (diffusion susceptibility, MIC, MBC)
Kirby-Bauer assay (diffusion susceptibility): uses a series of round filter paper disks impregnated with different antibiotics; a dispenser delivers up to 12 disks simultaneously to the surface of an agar plate covered by a bacterial lawn; inhibit growth of the lawn to different distances; zones of inhibition vary in width, depending on which antibiotic is used, the concentration of drug in the disk, and the susceptibility of the organism to the drug; the diameter of the zone around an antibiotic disk correlates to the MIC of that antibiotic against the organism tested; standardized to ensure reproducibility MIC: (the lowest concentration of the drug that will prevent the growth of an organism); antibiotic is serially diluted along a row of test tubes containing nutrient broth; after dilution, the organism to be tested is inoculated at identical low population densities into each tube, and the tubes are inoculated overnight; growth is seen as turbidity; the tube containing the MIC is the tube with the lowest concentration of drug that shows no growth; very useful for estimating a single drug's effectiveness against a single bacterial pathogen, but not practical when trying to screen 20 or more different drugs MBC: neither of the others can tell you whether a drug is bactericidal; to determine the minimum bactericidal concentration (MBC) of an antibiotic, a tube dilution test is performed and then the antibiotic is removed; antibiotic can be removed by pelleting cells in the "no growth" tubes by centrifugation and replacing the antibiotic-containing medium with fresh medium. If cells grow, they were not killed. The lowest concentration tube that still does not show growth represents the MBC almost any antibiotic can be both bactericidal at a high concentration (MBC) and bacteriostatic at a lower concentration (MIC). A drug, however, is deemed to have a bactericidal mode of action if its MBC is no more than four times its MIC
explain why mammalian viruses "uncoat" their genome and why bacteriophages do not
Mammalian viruses must disassemble their capsid to release genetic material once they are inside the host cell. A bacteriophage attaches to the cell surface by its tail fibers and then contracts to inject its DNA. the empty capsis remains outside as a "ghost"
List the key cellular structures in a eukaryotic cell and describe the function of each structure
Nucleus: "control center" of the cell Smooth Endoplasmic Reticulum: makes cellular products like hormones and lipids Rough Endoplasmic Reticulum: contains ribosomes on the surface responsible for the assembly of many proteins during translation Endoplasmic reticulum (genera)l: transport within the cell, lipid synthesis Lysosome: breakdown of nutrients, self-destruction of damaged or aged cells Peroxisome: neutralization of toxins Mitochondrion: aerobic ATP production Plasma Membrane: protect the cell from its surroundings Ribosomes: protein synthesis Golgi: exocytosis, secretion
explain how bidirectional semiconservative DNA replication copies bacterial chromosomes during cell division
Replication is called semiconservative because one parental strand is conserved and inherited by each daughter cell genome. It is called bidirectional because it begins at a fixed origin and progresses in opposite directions
describe how DNA transfer occurs during transformation, conjugation, transduction, and transposition
Transformation: the uptake by living cells of free-floating DNA from dead, lysed cells Conjugation: a DNA transfer process mediated by a transferable plasmid that requires cell-cell contact and formation of a protein complex between mating cells Transduction: the process hereby bacteriophages transfer fragments of bacterial DNA from one bacterium to another. Phage accidentally packages host genomic DNA instead of phage DNA. Host genomic DNA can now be transduced into another bacterium and incorporated into its genome Transposition: transposons (segments of DNA that move from one location to another in the same or different molecule) move by site-specific recombination from one DNA molecule to another. Composite transposons can carry a variety of genes, including antibiotic resistance genes. Result is a kind of frameshift insertion. Transposons all contain palindromic sequences at each end
explain how dessication and osmotic pressure control microbial growth
desiccation (drying) inhibits growth due to removal of water; used to preserve foods for thousands of years, does not prevent all microbial growth osmotic pressures: high concentrations of salt or sugar in foods to inhibit growth; cells in hypertonic solution of salt or sugar lose water; fungi have greater ability than bacteria to survive hypertonic environments
describe how dsDNA, ssDNA, dsRNA, +RNA, -RNA, and retroviruses replicate their genomes and translate their proteins
dsDNA: double-stranded DNA is transcribed to mRNA ssDNA: generates a double-stranded form within the host cell, which is transcribed to mRNA dsRNA: makes mRNA by using RNA-dependent RNA plymerase +RNA: single-stranded RNA (+) makes a complementary (-) strand, which is transcribed to mRNA -RNA: single-stranded RNA (-) is transcribed to mRNA retroviruses: single-stranded RNA (+) is reverse-transcribed to DNA, which is transcribed to mRNA
Distinguish the key traits of fungi, algae, amebas, alveolates, and tyrpanosomes
fungi: filaments or yeasts that usually lack motility; tough cell walls made of polysaccharides; heterotrophs by absorptive nutrition; include decomposers and parasites algae: chloroplast-containing protists that conduct photosynthesis amebas: heterotrophic protists with amorphous shape; motile with pseudopods alveolates: protists with flagella (flagellates) or cilia (ciliates); free-living prodators and host-dependent parasites; include ciliates, dinoflagellates, and apicomplexans tyrpanosomes: parasites with complex life cycles (typically two ore more hosts)
explain how antibiotic resistance spreads within bacterial communities
horizontal gene transfer: transformation, conjugation, transduction, and transposition
describe how ionizing and non-ionizing radiation affect microbial survival
ionizing: electron beams, gamma rays, X rays; destroys DNA; shorter wavelength equals more energy and greater penetration nonionizing: ultraviolet light; formation of thymine dimers inhibits DNA transcription and replication; UV light does not penetrate well; suitable for disinfecting air, transparent fluids, and surfaces of objects
describe transcriptional regulation of the lac operon and trp operon, and explain how the repressor's role differs in an inducible vs a repressible operon
lac operon: an Inducible Operon -default is "off": no lactose: repressor binds to operator and blocks transcription, with lactose: lactose binds to repressor, repressor fails to bind operator, transcription occurs; -lactose acts as an inducer; transcription ONLY occurs if an inducer is present trp operon: a Repressible Operon -default is "on": if corepressor (tryptophan) is present, the repressor protein binds to the promoter, blocking transcription. Transcription will always occur UNLESS tryptophan is present
explain the levels of disinfection (low, intermediate, high) and when it would be appropriate to use each level
low: kill vegetative bacteria, fungi, protozoa, and some viruses; used to disinfect items that contact skin only intermediate: kill fungal spores, protozoan cysts, viruses, and pathogenic bacteria; used to disinfect instruments that contact mucous membranes but are non-invasive high: kill all pathogens, including endospores; used to disinfect invasive instruments (e.g. scalpel)
compare and contrast refrigeration, freezing, and lyophilization
refrigeration and freezing: decrease microbial metabolism, growth, and reproduction; chemical reactions occur more slowly at low temperatures, liquid water not available refrigeration halts growth of most pathogens slow freezing is more effective than quick freezing; ice crystals puncture cell membranes during slow freezing lyophilization: bacteriostatic; used for long-term preservation of microbial cultures; rapid freezing that removes water through sublimation, prevents formation of damaging ice crystals
distinguish between sterilization, disinfection, antisepsis, and sanitation
sterilization: destruction of ALL living cells, spores, and/or viruses disinfection: removal of disease-causing microorganisms from inanimate surfaces; does not necessarily result in sterilization antisepsis: removal of disease-causing microorganisms from living tissues, such as skin or mucous membrane; does not necessarily result in sterilization sanitation: reduction of microbe numbers to "safe" levels to meet public health standards; does not necessarily result in sterilization
explain the relationship between transcription and translation in bacteria, and explain how this differs from eukaryotes
transcription and translation can occur simultaneously in prokaryotes; ribosomes attach at mRNA ribosome-binding sites and start synthesizing protein before transcription of gene is complete. in eukaryotes, RNA transcription occurs in the nucleus; mRNA is modified after transcription: 5' cap added, Poly(A) tail added, and introns spliced out: to prepare mRNA for exit into cytosol
