Biol 121- Impact of microbes

What are the three domains of life?

Bacteria, Archaea, and Eukaryotes.

How do Archaea differ from Bacteria in terms of cell wall composition?

Archaea lack peptidoglycan cell walls, whereas Bacteria possess them.

Why do smaller cells generally exhibit faster growth rates?

Smaller cells have a higher surface-to-volume ratio, which allows for a faster rate of nutrient exchange.

What are the four primary functions of the bacterial cell membrane?

Separation from the environment, acting as a selectively permeable barrier, serving as the site for respiration and photosynthesis, and energy conservation via the proton motive force.

What are the two main functions of the bacterial cell wall?

Determining/maintaining cell shape and protecting the cell from osmotic lysis.

What is the primary structural difference between Gram-positive and Gram-negative cell walls?

Gram-positive walls are ~90% peptidoglycan; Gram-negative walls have a thin peptidoglycan layer covered by an outer membrane of lipids, proteins, and lipopolysaccharides (LPS).

What color do Gram-positive and Gram-negative bacteria appear after a Gram stain?

Gram-positive appear purple; Gram-negative appear pink/red.

What are the two sugar components of peptidoglycan?

N-Acetylglucosamine (G) and N-Acetylmuramic acid (M).

How do lysozymes affect bacterial cells?

They break the bonds between N-Acetylglucosamine and N-Acetylmuramic acid, causing the cell to burst.

What is the function of a bacterial capsule?

Protection from host defenses and harsh environmental conditions, and attachment to surfaces.

What is the difference between fimbriae and pili?

Both are used for recognition and attachment, but pili are specifically required for mating.

Define the following flagellar arrangements: monotrichous, lophotrichous, and peritrichous.

Monotrichous: one flagellum; Lophotrichous: a cluster of flagella at one or both ends; Peritrichous: flagella spread over the entire surface.

What is a nucleoid in a bacterial cell?

An irregularly shaped region that serves as the location for the chromosome(s).

What are plasmids and why are they significant?

Small, circular DNA molecules that replicate independently; they are not required for growth but may carry genes for selective advantages like drug resistance.

What is the function of magnetosomes in bacteria?

They contain magnetite to help orient cells within magnetic fields.

What are endospores and what is their primary advantage?

Highly resistant structures formed by some Gram-positive bacteria under unfavorable conditions; they allow survival for thousands of years against heat, radiation, and drying.

What is the role of calcium dipicolinate in endospores?

It binds free water to help dehydrate the cell, contributing to its resistance.

What is the difference between chemically defined and complex media?

Chemically defined media have a known exact composition; complex media are made from digests of biological materials (like beef or milk) with unknown exact composition.

What is 'generation time' in bacterial growth?

The time required for a population to double in number.

What is the difference between a total count and a viable count of bacteria?

Total count uses non-specific dyes to count all cells; viable count uses fluorescent activity dyes to differentiate between live and dead cells.

What does a 'culturable count' measure?

It measures only the cells capable of forming colonies on solid media or increasing turbidity in liquid media.

What does it mean if a culture is 'viable but not culturable'?

The bacteria are alive and potentially pathogenic, but they cannot be grown using conventional laboratory media.

Why is turbidity used to measure bacterial growth?

It provides an indirect, rapid measurement of bacterial density by observing the cloudiness of the suspension.

What are the three properties shared by all cells?

Compartmentalization, metabolism, and growth/evolution.

What are the three properties shared by only some cells?

Motility, differentiation, and communication.

What does a spectrophotometer measure to determine turbidity?

Transmission or absorbance of light.

What is the primary difference between bacteriostatic and bactericidal agents?

Bacteriostatic agents stop growth without killing bacteria, while bactericidal agents kill bacteria by disrupting vital processes.

How do bacteriolytic agents differ from other antimicrobial agents?

They destroy bacteria completely by lysing their cell walls, leading to a decrease in total cell number.

What is the difference between heterotrophs and autotrophs regarding carbon sources?

Heterotrophs require organic molecules made by other organisms, whereas autotrophs use CO2 as their principal carbon source.

How do phototrophs and chemotrophs differ in energy acquisition?

Phototrophs use light as an energy source to produce ATP, while chemotrophs oxidize organic or inorganic compounds.

What are mesophiles in the context of bacterial temperature tolerance?

Bacteria that thrive at moderate temperatures, such as those commonly found in the human body.

What distinguishes halophiles from other bacteria?

Halophiles are bacteria that grow in habitats with high salt concentrations.

Define 'host' in the context of microbiology.

An organism that supports the growth of viruses, bacteria, or parasites.

What is the difference between pathogenicity and virulence?

Pathogenicity is the ability to cause disease, while virulence is the degree or intensity of that pathogenicity.

How is 'infection' distinguished from 'disease'?

Infection is the persistence of bacteria in a host without necessarily causing tissue damage; disease is overt damage where body functions are impaired.

What was the Miasma theory of disease?

The belief that epidemics originated from 'bad air' or rotting organic matter.

What is the core principle of Robert Koch's germ theory of disease?

That one specific organism causes one specific disease.

What are opportunistic pathogens?

Pathogens that only cause serious disease when the host's immune defenses are impaired.

What are primary (obligate) pathogens?

Pathogens capable of causing disease in the absence of immune defects, relying on host nutrients and cellular machinery to survive.

What is a reservoir in the context of bacterial pathogens?

A necessary source where a pathogen lives and multiplies, such as humans, animals, or the environment.

What are fomites?

Non-living materials or objects (like food, water, or soil) that act as passive vectors for transmitting pathogens.

What is the definition of colonization in infectious disease?

The establishment of a stable population of bacteria in the host, requiring successful competition for nutrients and attachment sites.

Why is adherence critical for bacterial pathogens?

It allows bacteria to overcome host flushing mechanisms and remain attached to host cell surfaces.

What is the definition of a pathogen?

An organism that causes disease by impairing or interfering with the normal physiological activities of the host.

What are acidophiles and alkaliphiles?

Acidophiles are bacteria that grow best in acidic habitats, while alkaliphiles grow best in alkaline habitats.

What is the significance of Geogemma barossii?

It is a record-holding thermophile that grows between 80-121°C and can survive at 130°C for at least two hours.

What are two examples of indirect host-to-host transmission?

Vector-borne transmission (e.g., ticks, rats) and transmission via fomites.

What are the two stages of bacterial adhesion to surfaces?

The 1st stage involves non-specific forces like charge and hydrophobicity; the 2nd stage involves specific bacterial adhesins and host receptors.

List four examples of bacterial adhesins.

Fimbriae, pili, capsules, slime layers, flagella, and lipoteichoic acids.

How does the eye protect against bacterial colonization?

Lysozyme in the eye dissolves bacterial cell walls.

What is the function of invasins in bacterial pathogenesis?

Invasins are virulence factors that allow bacteria to penetrate into, through, or between host cells.

Name three lytic compounds used by bacteria to facilitate tissue invasion.

Collagenase, phospholipases, and haemolysins.

How do bacteria avoid phagocytosis?

By producing structures that prevent effective contact, such as capsules and special surface proteins.

What is antigenic variation in the context of immune evasion?

It is the process of switching between different types of surface structures to avoid recognition by antibodies.

What systems do bacteria use to acquire iron for growth?

They express high-affinity iron uptake systems, specifically siderophores and direct binding of iron transport proteins.

What is the primary difference between exotoxins and endotoxins?

Exotoxins act on specific targets and are secreted, while endotoxins are bound to the bacterial cell and have indirect effects.

What is the mechanism of action for the cholera toxin?

It causes hypersecretion of water and chloride ions in the gut, leading to severe dehydration.

What are the clinical effects of endotoxins released by gram-negative bacteria?

They can cause fever, shock, blood coagulation, and inflammation by activating various host systems.

How are the three domains of life classified?

Based on sequence data for ribosomal RNA (rRNA): Eukarya, Archaea, and Bacteria.

What are the three main components of the protist cytoskeleton?

Actin filaments, microtubules, and intermediate filaments.

What distinguishes photoautotrophic protists from other groups?

They possess plastids (chloroplasts) for photosynthesis and are generally referred to as algae.

What defines a heterotrophic protist (protozoa)?

They feed on bacteria, fungi, or other protists and lack a cell wall.

What is a mixotrophic protist?

A protist that can both photosynthesize and ingest food; they do not have a cell wall.

What is the function of a contractile vacuole in protists?

It expels excess water from the cell to prevent lysis in protists that lack a cell wall.

What are the advantages of cyst formation in protists?

Cysts are highly resistant to heat, drying, and radiation, have low water content, and can survive for long periods in unfavorable conditions.

How do protists differ from bacteria regarding genetic reproduction?

Bacteria reproduce via binary fission, while protists reproduce via mitosis.

What are hydrogenosomes in protists?

They are anaerobic mitochondria that use pyruvate to produce hydrogen, acetate, and CO2.

What does the endosymbiont theory propose regarding mitochondria and plastids?

It proposes that mitochondria originated from an alpha-proteobacterium and chloroplasts originated from a cyanobacterium living as endosymbionts.

Why do non-motile photosynthetic protists have cell walls?

To provide structural support and protection, as they lack the motility mechanisms of other protists.

What is the primary role of normal flora on the skin?

They inhibit the growth of pathogens.

How does the stomach pH act as a barrier to infection?

The acidic environment inhibits or kills many ingested bacteria.

What is the significance of the Lipid A component in gram-negative bacteria?

It is the part of the lipopolysaccharide that possesses endotoxin activity.

What evidence supports the endosymbiotic origin of organelles?

Organelles are similar in size to bacteria, possess their own circular DNA, replicate by binary fission, contain bacterial-type ribosomes, and have a double membrane.

What is organellar mixotrophy?

A process where a protist consumes algal cells but does not digest the plastids, allowing them to photosynthesize temporarily until the plastids need replenishing.

How does cellular mixotrophy differ from organellar mixotrophy?

In cellular mixotrophy, the protist consumes algae but does not digest them; the algae continue to divide within the host cell via endosymbiosis.

What characterizes constitutive mixotrophs?

Endosymbiotic algae have evolved into permanent organelles through genetic transfer, making the protist dependent on them for survival.

What are the two types of nuclei found in ciliates and their functions?

The macronucleus (general cell function) and the micronuclei (used for sexual reproduction).

What is the structural difference between motile and non-motile cilia?

Motile cilia have a 9+2 microtubule arrangement with dynein motor proteins, while non-motile cilia have a 9+0 arrangement and lack dynein.

What are membranelles in ciliates?

Stiffer cilia located in the cytostome used to filter and direct prey into the food vacuole.

How do Suctorian ciliates feed?

They use microtubule tentacles to pierce prey and suck out the contents, a form of raptorial feeding.

How do ciliates reproduce sexually?

Through conjugation, which involves meiosis and mitosis with the exchange of haploid micronuclei to increase genetic variation.

What is the primary difference in binary fission between ciliates and flagellates?

Ciliates undergo transverse binary fission, whereas flagellates undergo longitudinal binary fission.

What is the function of the eyespot (stigma) in phytoflagellates?

It contains carotenoid lipid globules that shade photoreceptors, allowing the cell to detect light direction for movement.

What is the role of the second flagellum in dinoflagellates?

It is located around the waist and causes the cell to rotate while swimming.

How do naked amoebae move and feed?

They move via cytoplasmic streaming and form pseudopodia on surfaces to capture prey through raptorial feeding.

What are the three cell forms of naked amoebae?

Trophozoites (feeding form), cysts (resting stage), and a floating form used for dispersal.

How do foraminiferans and radiolarians differ in their test composition?

Foraminiferans have tests made of calcium carbonate (CaCO3), while radiolarians have tests made of silica.

What is the 'microbial loop' in aquatic ecosystems?

A food web structure where bacteria consume leaked sugars from photoautotrophs, and heterotrophic protozoa consume both bacteria and photoautotrophs.

How do heterotrophic protozoa contribute to nutrient cycling?

Through remineralization, they release phosphorus (PO4) and nitrogen (NH4) during the digestion of their prey.

Why do amoebae act as reservoirs for pathogenic bacteria?

Because amoebae and human macrophages share similar digestion-evasion mechanisms, allowing bacteria to 'practice' surviving inside amoebae before infecting human immune cells.

What is the function of the dynein motor protein in cilia?

It allows the cilia to move by interacting with the microtubule structure.

What are cirri in ciliates?

Clumps of fused cilia used for movement.

What distinguishes Choanoflagellates from other flagellates?

They possess a collar of contractile tentacles (microvilli) and are more closely related to animals than other protists.

What is the feeding mechanism of heliozoans?

They use diffusion feeding, extending sticky axopodia to capture prey.

What is the ecological impact of protozoan predation on bacteria?

It prevents bacteria from reaching the stationary phase, keeping them in the log phase where they are constantly feeding and dividing.

How do flagellates move compared to ciliates?

Flagellates move in a propeller-like motion, whereas ciliates use coordinated rows of cilia for swimming.

What is the purpose of the lorica in certain ciliates?

It acts as a shell that provides protection and structural strength.

Do amoebae feed in their floating form?

No, they are too stiff to wrap pseudopodia around prey in the floating form.

What percentage of human cells are estimated to be bacterial?

90% of human cells are bacterial.

What is the primary site of bacteria in the human body?

The gut.