Chapter 27: Bacteria and Archaea Flashcards

Comprehensive practice flashcards covering structural features, metabolism, genetics, phylogenetic diversity, and ecological impacts of Bacteria and Archaea based on lecture notes.

How do prokaryotic cells compare in size to eukaryotic cells?

Prokaryotic cells are typically $0.5\text{–}5\,\mu\text{m}$ in diameter, which is significantly smaller than eukaryotic cells ($10\text{–}100\,\mu\text{m}$).

What key structural component forms the cell wall of Bacteria, and how does Archaea differ?

Bacterial cell walls contain peptidoglycan, a network of sugar polymers and polypeptides. Archaea cell walls lack peptidoglycan and are composed of other polysaccharides and proteins.

What structural cell wall difference distinguishes Gram-positive bacteria from Gram-negative bacteria?

Gram-positive bacteria have a thick cell wall composed of peptidoglycan that stains a darker color. Gram-negative bacteria have a thinner peptidoglycan layer located between the plasma membrane and an outer membrane containing lipopolysaccharides.

How do capsules and slime layers differ, and what are their primary survival functions?

A capsule is a dense and well-defined sticky layer of polysaccharide or protein, whereas a slime layer is not well organized. Both function in adherence, protection, and preventing dehydration.

What are endospores, and under what conditions do prokaryotes form them?

Endospores are metabolically inactive, protected copies of a bacterium's chromosome formed when water or nutrients are lacking. They can withstand extreme conditions and remain viable for centuries.

What are the primary survival functions of fimbriae, pili, and flagella in prokaryotes?

Fimbriae allow prokaryotes to attach to substrates or other cells; pili pull cells together enabling DNA exchange during conjugation; flagella provide motility for directional movement toward or away from stimuli (taxis).

How is genetic material stored and organized inside a prokaryotic cell?

Prokaryotic genetic material is stored as a single circular chromosome located in a membrane-less nucleoid region, along with small, independently replicating rings of DNA called plasmids.

What mechanisms enable prokaryotic populations to adapt rapidly to new environmental pressures?

Rapid reproduction via binary fission with short generation times (dividing every $1\text{–}3\,\text{hours}$ optimal) allows random mutations to accumulate quickly across large populations, facilitating swift natural selection.

How do transformation, transduction, and conjugation differ as mechanisms of horizontal gene transfer?

Transformation involves taking up foreign DNA from the surroundings; transduction is the viral transfer of bacterial genes by bacteriophages; conjugation is the direct transfer of DNA (such as a plasmid) between two temporarily joined bacterial cells.

What distinguishes an Hfr donor cell from an F+ donor cell during bacterial conjugation?

An $F^+$ cell carries the F factor on a separate plasmid and donates a plasmid. An Hfr cell has the F factor integrated into its main circular chromosome and can donate chromosomal DNA.

What typically happens to an F- recipient cell following conjugation with an Hfr donor cell?

The recipient cell typically remains an $F^-$ cell because the mating bridge usually breaks before the entire chromosome containing the full F factor is transferred, resulting in a recombinant $F^-$ cell.

How are prokaryotic organisms categorized based on their energy and carbon sources?

Photoautotrophs use light for energy and $CO_2$ (or related compounds) for carbon; Chemoautotrophs use inorganic chemicals (such as $H_2S$, $NH_3$, or $Fe^{2+}$) for energy and $CO_2$ for carbon; Photoheterotrophs use light for energy and organic compounds for carbon; Chemoheterotrophs use organic compounds for both energy and carbon.

How do obligate aerobes, obligate anaerobes, and facultative anaerobes respond to oxygen?

Obligate aerobes require $O_2$ for cellular respiration; obligate anaerobes are poisoned by $O_2$ and live by fermentation or anaerobic respiration; facultative anaerobes can use $O_2$ when present or carry out fermentation/anaerobic respiration when $O_2$ is absent.

What is nitrogen fixation, and why is it ecologically vital?

Nitrogen fixation is the conversion of atmospheric nitrogen ($N_2$) into ammonia ($NH_3$). It is essential because it provides usable nitrogen required for the synthesis of amino acids and nucleic acids across the biosphere.

What specialized cells in filamentous cyanobacteria are dedicated to nitrogen fixation?

Heterocysts.

What metabolic modes are represented within the bacterial clade Proteobacteria?

Proteobacteria is a vast group of Gram-negative bacteria that includes photoautotrophs, chemoautotrophs, and heterotrophs.

What pathogenic heterotrophic proteobacteria cause gonorrhea, cholera, and stomach ulcers?

Neisseria gonorrhoeae causes gonorrhea, Vibrio cholerae causes cholera, and Helicobacter pylori causes stomach ulcers.

What are the defining structural characteristics and lifestyle of Chlamydias?

Chlamydias are Gram-negative bacteria that survive exclusively as obligate intracellular parasites inside animal cells.

Which bacterium causes nongonococcal urethritis, the most common STI in the United States?

Chlamydia trachomatis.

What are Spirochetes, and how do they move through their environment?

Spirochetes are helical Gram-negative heterotrophs that spiral through the environment by rotating internal filaments.

Which pathogenic Spirochetes cause syphilis and Lyme disease?

Treponema pallidum causes syphilis, and Borrelia burgdorferi causes Lyme disease.

Why are Cyanobacteria evolutionarily significant to plant evolution and Earth's atmosphere?

Cyanobacteria are Gram-negative photoautotrophs that were the first organisms to release significant quantities of $O_2$ into Earth's atmosphere and are the likely endosymbiotic ancestors of modern plant chloroplasts.

What are Actinomycetes, and why is the genus Streptomyces clinically important?

Actinomycetes are colony-forming Gram-positive bacteria; Streptomyces is cultured as a major source of medical antibiotics.

Which characteristics distinguish Domain Archaea from Bacteria and Eukarya?

Archaea lack peptidoglycan in their cell walls, have several kinds of RNA polymerase, use Methionine as the initiator amino acid for protein synthesis, contain some branched hydrocarbon membrane lipids, and lack a nuclear envelope and membrane-enclosed organelles.

What defines extreme halophiles and extreme thermophiles within Domain Archaea?

Extreme halophiles tolerate or require highly saline environments; extreme thermophiles possess adaptations that stabilize their DNA and proteins at temperatures above $100^\circ\text{C}$.

What are Methanogens, and in what types of environments are they found?

Methanogens are obligate anaerobes that produce methane ($CH_4$). They live in diverse anaerobic environments such as under kilometers of ice in Greenland, in swamps and marshes, and in the guts of cattle and termites.

Which archaeal clades make up the TACK supergroup?

Thaumarchaeota, Aigarchaeota, Crenarchaeota (which includes most extreme thermophiles), and Korarchaeota.

How do exotoxins differ from endotoxins in pathogenic bacteria?

Exotoxins are proteins secreted by bacteria that cause disease even if the bacteria are not present (e.g., Vibrio cholerae). Endotoxins are outer membrane components of Gram-negative bacteria released only when bacteria die and their cell walls break down (e.g., Salmonella).

Which mutualistic gut bacterium in human intestines synthesizes carbohydrates, vitamins, and other essential nutrients?

Bacteroides thetaiotaomicron.

In the long-term evolution experiment by Cooper and Lenski, what happened to Escherichia coli populations over 20,000 generations?

The experimental E. coli populations evolved an increased population growth rate relative to the ancestral population as a result of beneficial mutations accumulating over time.

What were the findings regarding the novel antibiotic teixobactin compared to vancomycin in treating MRSA infections in mice?

Teixobactin, isolated from unculturable soil bacteria, reduced the number of MRSA (Staphylococcus aureus) colonies just as effectively as vancomycin at both low ($1.0\,\text{mg/kg}$) and high ($5.0\,\text{mg/kg}$) doses.

In the evolutionary tree of lizards shown, what is the sister taxon to iguanas?

The group consisting of monitor lizards and glass lizards.

What role do R plasmids play in bacterial populations?

R plasmids carry genes for antibiotic resistance and enable the rapid spread of resistance within and among bacterial species via conjugation.

What term describes the use of organisms to remove pollutants from the environment?

Bioremediation.