Prokaryotic and Eukaryotic Microorganisms and Acellular Infectious Agents

Comprehensive practice flashcards detailing cell biology, comparative structural morphology, taxonomy, and acellular agents across prokaryotes, eukaryotes, viruses, viroids, and prions.

How do prokaryotic and eukaryotic cells differ in typical cell size?

Prokaryotic cells typically range from $1-10\,\mu\text{m}$ in size, whereas eukaryotic cells typically range from $10-200\,\mu\text{m}$ in size.

How is chromosomal DNA compacted and stored in prokaryotic versus eukaryotic cells?

Prokaryotes compact their DNA via supercoiling into a single circular chromosome located in the cytoplasm (nucleoid), whereas eukaryotes wrap linear DNA around histone proteins to form chromatin and chromosomes enclosed inside a membrane-bound nucleus.

What are the sedimentation coefficients and subunit compositions of prokaryotic versus eukaryotic ribosomes?

Prokaryotes possess $70\text{S}$ ribosomes composed of a $50\text{S}$ large subunit ($23\text{S}$ and $5\text{S}$ rRNAs, $34$ proteins) and a $30\text{S}$ small subunit ($16\text{S}$ rRNA, $21$ proteins). Eukaryotes possess $80\text{S}$ ribosomes composed of a $60\text{S}$ large subunit ($28\text{S}$, $5.8\text{S}$, and $5\text{S}$ rRNAs, ~$45$ proteins) and a $40\text{S}$ small subunit ($18\text{S}$ rRNA, ~$30$ proteins).

How do the chemical linkages and fluidity-regulating lipids of cell membranes differ among bacteria, archaea, and eukaryotes?

Bacteria and eukaryotes utilize ester linkages in their phospholipids and regulate membrane fluidity using hopanoids (bacteria) or cholesterol (eukaryotes). Archaea utilize ether linkages in their phospholipids.

How do passive transport and active transport differ in terms of cellular energy and solute movement?

Passive transport (diffusion, facilitated diffusion via channels or carrier proteins, and osmosis) moves solutes down their concentration gradient without requiring ATP. Active transport moves solutes against their concentration gradient and requires ATP.

What are the primary chemical components of the cell walls in bacteria, archaea, fungi, and algae?

Bacterial cell walls contain peptidoglycan (murein); archaeal cell walls contain pseudopeptidoglycan (pseudomurein); fungal cell walls contain chitin; and algal cell walls contain cellulose, pectins, and agar.

In the archaeal cell wall component pseudopeptidoglycan, which two alternating amino sugars form the polysaccharide backbone?

N-acetylglucosamine (NAG) and N-acetyltalosaminuronic acid (NAT).

What structural and operational differences distinguish prokaryotic flagella from eukaryotic flagella?

Prokaryotic flagella are composed of flagellin, spin like a propeller, and are powered by a $\text{Na}^+$ or $\text{H}^+$ proton gradient. Eukaryotic flagella are composed of microtubules, move in a wave-like pattern, and are driven by $\text{ATP}$.

What three main structural regions compose the bacterial flagellum shown in this diagram?

The filament, the hook, and the basal apparatus (which anchors into the cell wall and plasma membrane).

What four unique prokaryotic surface structures are used specifically for attachment?

Fimbriae, pili (including conjugation pili), capsules, and slime layers.

What are the five sequential stages of biofilm formation depicted in this life cycle diagram?

(1) Attachment to surface, (2) Formation of monolayer and production of matrix, (3) Microcolony formation, multi-layer, (4) Mature biofilm, with characteristic "mushroom" formed of polysaccharide, and (5) Detachment and reversion to planktonic growth, starting a new cycle.

What is quorum sensing and what role does it play in biofilm development?

Quorum sensing is a bacterial communication process in which bacteria secrete and detect chemical signaling molecules that coordinate collective behaviors, triggering bacterial congregation and biofilm formation once a population threshold is reached.

What survival advantages do biofilms provide to prokaryotes, and what is their annual economic cost to the U.S. oil and gas industry?

Biofilms protect prokaryotes from predators and provide resistance to chemicals including antibiotics, disinfectants/antiseptics, and biocides. They cause equipment corrosion that costs the U.S. oil and gas industry between $\$5$ and $\$12\text{ billion per year}$.

Which bacterium forms biofilms in cystic fibrosis patients that lead to fatal lung infections?

Pseudomonas aeruginosa.

What are the specific functions of inclusion bodies, plasmids, and endospores in prokaryotes?

Inclusion bodies store/hoard nutrients and materials; plasmids carry accessory non-essential genes that confer extra phenotypic traits (such as antibiotic resistance); and endospores are dormant, highly resistant structures produced to survive extreme stressors (heat, starvation, desiccation, antiseptics/disinfectants).

What are the primary functions of the Golgi body, lysosome, and peroxisome in eukaryotic microbes?

The Golgi body is responsible for packaging, modifying, and shipping cellular products; the lysosome is responsible for cellular digestion; and the peroxisome breaks down toxic peroxides.

What major contribution did Carl Woese make to biological classification?

He discovered the Archaea and pioneered ribosomal RNA/DNA-based phylogenetic studies, establishing that all cellular life diverged from a common ancestor into three distinct domains: Bacteria, Archaea, and Eukarya.

What rules govern the binomial nomenclature system established by Carolus Linnaeus?

Organisms receive a two-part Latin name: the genus name comes first, is capitalized, and underlined/italicized; the species name comes second, is in lowercase, and underlined/italicized.

What are the etymological origins of the names Escherichia coli and Staphylococcus aureus?

Escherichia coli is named honorarily after Theodor Escherich and descriptively for its habitat (the colon). Staphylococcus aureus is named descriptively for clustered spherical cells ("staphyle" = grape cluster, "coccus" = circle) and gold-pigmented colonies ("aureus" = gold).

Which two scientists are honored in the binomial name Shigella flexneri?

Kiyoshi Shiga and Simon Flexner.

What are the distinct structural features of Gram-positive, Gram-negative, and acid-fast bacterial cell walls shown in this comparative diagram?

Gram-positive cell walls have a thick peptidoglycan layer containing teichoic and lipoteichoic acids over a single inner membrane (stains purple). Gram-negative cell walls have a thin peptidoglycan layer, a periplasmic space, and an outer membrane containing LPS and porins (stains red/pink). Acid-fast cell walls contain a lipid-rich layer of mycolic acids, arabinogalactan, and lipoarabinomannan anchored to peptidoglycan.

What percentage of bacterial species have been discovered, and what percentage of all bacteria are pathogenic?

Only about $1\%$ of bacterial species have been discovered, and less than $1\%$ of known bacteria are pathogenic.

What distinguishes the bacterial species Mycoplasma pneumoniae from typical bacteria?

Mycoplasma pneumoniae naturally lacks a cell wall entirely, possessing only a plasma membrane as its outer boundary.

What ecological role is performed by the marine bacterium Alcanivorax?

Alcanivorax feeds on crude oil and secretes natural emulsifiers that break up oil droplets at the oil-water interface.

What specialized photosynthetic pigment allows some Archaea to perform autotrophic energy generation?

Bacteriorhodopsin.

Which two archaeal genera exhibit irregular and flat box-like cellular morphologies, respectively?

Thermoplasma possesses an irregular shape, and Haloquadratum possesses a flat, box-like (square) shape.

What are the defining environmental characteristics and genus examples of the archaeal phyla Crenarchaeota and Euryarchaeota?

Crenarchaeota are mostly hyperthermophiles growing above $80^\circ\text{C}$ in sulfur-rich environments (examples: Sulfolobus, Thermoproteus, Pyrolobus). Euryarchaeota include a broad mix of hyperthermophiles, extreme halophiles, methanogens, and acidophiles (examples: Thermoplasma, Halobacterium, Methanobacterium).

How do yeasts and molds differ in cellularity and reproduction?

Yeasts are unicellular fungi that typically reproduce asexually via budding, whereas molds are multicellular fungi composed of filamentous hyphae forming mycelia that reproduce via sexual and asexual spores.

Which zygomycete species typically causes opportunistic fungal infections in patients with diabetes or leukemia?

Rhizopus.

What toxin is produced by Aspergillus species, on what foods does it accumulate, and what pathology does it cause?

Aspergillus produces aflatoxin on contaminated peanuts and grains, which causes cancer; the mold also causes opportunistic pulmonary infections in cancer patients.

What fungal division do edible mushrooms belong to, and what is their characteristic spore-producing club structure called?

Basidiomycetes ("club fungi"), which produce sexual basidiospores on club-shaped structures called basidia.

Identify the primary locomotion and feeding extension indicated on this amoeba diagram.

Pseudopod.

What are the distinct clinical features and transmission modes of the protozoans Giardia lamblia and Trichomonas vaginalis?

Giardia lamblia (a diplomonad) produces durable cysts, is transmitted via untreated drinking water from lakes/streams, and causes "hiker's diarrhea." Trichomonas vaginalis (a parabasalid) does not produce cysts, is transmitted sexually, and causes burning urination/vaginal discharge, though many men are asymptomatic. Both lack mitochondria and are flagellated.

Which insect vectors transmit African sleeping sickness and Chagas disease caused by Trypanosoma species?

The tsetse fly transmits African sleeping sickness, and the kissing bug transmits Chagas disease.

What structural feature provides motility in Paramecium species, and how many nuclei do they possess?

Paramecium species move via cilia and possess two nuclei (a macronucleus and a micronucleus).

Which non-motile group of protozoa causes malaria, toxoplasmosis, and cryptosporidiosis?

Apicomplexans.

What commercial polysaccharide products are harvested from red algae and brown algae (kelp)?

Agar is harvested from red algae, and alginate is harvested from brown algae.

What group of armored algae with two perpendicular flagella causes red tides and paralytic shellfish poisoning?

Dinoflagellates.

Why are Oomycetes (water molds) classified with algae rather than true fungi?

Although Oomycetes form filamentous hyphae and produce sporangiospores similar to fungi, their DNA sequence analysis shows they are most closely related to brown algae.

How are the three major parasitic helminths in the roundworm (nematode) group characterized clinically?

Pinworms live in the digestive tract, cause perianal itching, and represent the most common worm infection in the U.S. (enterobiasis). Hookworms dwell in soil in the southern U.S. and cause anemia and protein deficiency. Heartworms infect the hearts of dogs and cats via mosquito bites.

What vector transmits infective microfilariae/larvae to dogs and cats in the heartworm life cycle shown?

Mosquitoes.

What two therapeutic pharmaceutical agents are co-administered to treat canine heartworm infections?

Immiticide (melarsomine dihydrochloride) and doxycycline.

According to Table 3.1, how do viruses differ from cellular organisms regarding growth, reproduction, responsiveness, and metabolism?

Viruses do not undergo growth in size, rely entirely on a host cell to replicate, exhibit responsiveness only as reactions to host cells in some species, and do not possess independent metabolism, utilizing host cell machinery instead.

What two essential components are present in all viruses at minimum?

A protein coat called a capsid and a nucleic acid genome (either DNA or RNA).

Provide representative viral examples for each of the four possible viral genetic material configurations: dsDNA, ssDNA, ssRNA, and dsRNA.

dsDNA: Variola virus (smallpox); ssDNA: Parvovirus; ssRNA: Influenza virus, Norovirus, and Covid-19; dsRNA: Rotavirus.

What do the terms viral host range and viral tropism describe?

Host range refers to the breadth of host species a virus can infect (e.g., broad for influenza/SARS-CoV-2, narrow for most bacteriophages). Tropism refers to the specific tissue or cell types within a host that a virus infects (e.g., hepatitis targeting liver hepatocytes, Ebola targeting endothelial, ocular, and hepatic cells).

How do bacteriophage lytic and lysogenic replication pathways differ?

In the lytic cycle, the phage injects its DNA, directs synthesis of virions, and lyses the bacterial host cell. In the lysogenic cycle, phage DNA recombines into the bacterial chromosome as a latent prophage, replicating passively during cell division until induced to excise and enter the lytic pathway.

What two unique steps distinguish animal virus replication from bacteriophage replication?

Animal viruses enter the host cell as entire virions (rather than injecting naked genome) and must undergo an uncoating step to release the nucleic acid from the capsid inside the cytoplasm.

How does HIV establish a permanent chronic persistent infection in animal host cells?

HIV uses reverse transcriptase to transcribe its ssRNA genome into dsDNA, which stably integrates into the host chromosome to form a provirus that continuously sheds new virions without releasing or excising the integrated proviral sequence.

What is the defining clinical characteristic of latent persistent viral infections like Herpes simplex and Varicella-Zoster virus (VZV)?

They undergo periodic asymptomatic phases of dormancy (latency) during which virions are undetectable, punctuated by episodic flare-ups where virions replicate, shed, and cause recurrent disease symptoms.

Match the following viral infection terms with their exact definitions: virulent virus, persistent virus, latent virus, fusogenic virus, and oncogenic virus.

Virulent virus: lyses its host cell (e.g., Influenza, Norovirus); Persistent virus: continuously shed from host cells over time (e.g., HIV); Latent virus: goes dormant with periodic reactivation (e.g., Herpes, VZV); Fusogenic virus: promotes cell-cell fusion into giant multinucleated cells (e.g., RSV); Oncogenic virus: causes cancer (e.g., human papillomaviruses).

What cytopathic process is illustrated where viral fusion proteins cause neighboring uninfected cells to merge into a single multinucleated mass?

Syncytium formation (characteristic of fusogenic viruses like RSV).

What clear visible zones indicate bacteriophage replication on a lawn of host bacteria in a petri plate?

Plaques.

What is a viroid and how does its structural composition differ from a conventional virus?

A viroid is an infectious circular piece of naked RNA that completely lacks a protein coat (capsid).

What are prions and what neuropathological structures do they form in brain tissue?

Prions are infectious, improperly folded proteins that induce misfolding of normal neurological proteins, destroying neurons and aggregating into dense masses termed amyloids.

What are the specific animal hosts for Scrapie, Bovine Spongiform Encephalopathy (BSE), Chronic Wasting Disease (CWD), and Creutzfeldt-Jakob Disease (CJD)?

Scrapie infects sheep; BSE infects cattle; CWD infects deer; and CJD infects humans.

What are seven confirmed clinical routes by which human prion diseases can be acquired or transmitted?

(1) Genetic inheritance, (2) consumption of infected food products, (3) administration of cadaveric pituitary growth hormone, (4) surgical implantation of cadaveric dura mater, (5) contaminated neurosurgical instruments, (6) corneal grafts, and (7) blood transfusions.