Microbiology

What are the key characteristics of prokaryotic cells regarding their DNA and organelles?

They do not have a nucleus, keep their DNA in a non-membrane-bound area called the nucleoid, usually have one circular chromosome, and do not usually have membrane-bound organelles.

What is the size of ribosomes in prokaryotic cells versus eukaryotic cells?

Prokaryotic cells have $70S$ ribosomes, while eukaryotic cells have $80S$ ribosomes in the cytoplasm.

List the main characteristics of eukaryotic cells.

They are usually larger and more complex, have a nucleus surrounded by a nuclear envelope, contain several linear chromosomes, have membrane-bound organelles, a cytoskeleton, an endomembrane system, and reproduce through mitosis or meiosis.

What is the major structural difference between prokaryotic and eukaryotic cells?

Eukaryotic cells are compartmentalized, meaning their structures and chemical processes are separated into organelles, while prokaryotic cells generally carry out processes in the cytoplasm or plasma membrane.

Define Bacteria.

Unicellular prokaryotes that lack a nucleus or membrane-bound organelles, typically have cell walls containing peptidoglycan, and can be helpful, harmless, or pathogenic.

What are Protists?

A diverse informal group of eukaryotes that are not classified as plants, animals, or fungi, including algae, protozoa, and fungus-like protists.

What is the composition of fungal cell walls and their two physical forms?

Their cell walls usually contain chitin, and they include unicellular yeasts and multicellular molds.

Why are Helminths included in the study of microbiology?

They are multicellular parasitic worms that, while often visible as adults, have microscopic eggs and larvae and cause infectious diseases.

What is the structure of a virus?

They are acellular and contain either DNA or RNA inside a protein coat called a capsid; some also possess an envelope.

What are Endospores?

Dormant protective structures produced inside certain bacteria when conditions are unfavorable to protect bacterial DNA; they are not used for reproduction.

Define Peptidoglycan.

A mesh-like material found only in bacterial cell walls made from alternating NAM and NAG sugars connected by peptide chains.

What is the difference between Fimbriae and Pili?

Fimbriae are short, numerous, bristle-like structures for attachment, while Pili are longer, less numerous structures; a specialized sex pilus transfers DNA between bacterial cells.

Define Chemotaxis and Phototaxis.

Chemotaxis is directional movement in response to a chemical, whereas phototaxis is directional movement in response to light.

In bacterial movement, what is a 'run' and a 'tumble'?

A run is purposeful forward movement with flagella rotating counterclockwise; a tumble is a random movement that changes direction with flagella rotating clockwise.

Why would a bacterium undergo sporulation?

When nutrients are depleted or environmental conditions become unfavorable, to protect the bacterial chromosome until conditions improve.

What are the six steps of sporulation?

1. A septum forms; 2. Chromosome enclosed in a forespore; 3. Mother cell surrounds forespore with a second membrane; 4. Thick cortex forms; 5. Protective spore coat forms; 6. Mother cell breaks down and releases the mature endospore.

Compare Gram-positive and Gram-negative cells.

Gram-positive cells have a thick peptidoglycan wall, teichoic acids, no outer membrane, and stain purple. Gram-negative cells have a thin peptidoglycan layer, a periplasmic space, an outer membrane containing lipopolysaccharide ($LPS$), and stain pink/red.

What is Lipopolysaccharide ($LPS$) and its clinical significance?

A molecule in the outer membrane of gram-negative bacteria; its lipid A portion acts as an endotoxin.

What does it mean if a fungus is dimorphic?

It can grow in two different forms, usually yeast or mold, depending on environmental conditions like temperature (e.g., Histoplasma capsulatum).

Define the fungal groups Ascomycota and Basidiomycota based on their spores.

Ascomycota produce sexual spores called ascospores in a sac-like ascus. Basidiomycota produce sexual spores called basidiospores on club-like basidia.

What are protozoan Trophozoites and Cysts?

A trophozoite is the active feeding stage, while a cyst is a protective form some protozoans take during unfavorable conditions.

What is Schizogony?

A form of asexual reproduction where the nucleus divides several times before the cell divides into many smaller cells called merozoites.

Define Monoecious and Dioecious in helminths.

Monoecious means one individual has both male and female reproductive organs; Dioecious means each individual has either male or female organs.

Contrast Homolactic and Heterolactic fermentation.

Homolactic fermentation produces only lactic acid; Heterolactic fermentation produces a mixture of lactic acid, ethanol and/or acetic acid, and $CO_2$.

What is Bioremediation?

The use of microorganisms to break down or remove environmental pollutants, changing them into less harmful substances.

What are the differences between Synthetic, Natural, and Semisynthetic antimicrobials?

Synthetic is produced from chemicals not found in nature; Natural is produced by a microorganism; Semisynthetic is a natural antibiotic chemically modified for better stability or effectiveness.

Define Pathogenicity and Virulence.

Pathogenicity is the ability to cause disease; Virulence is the degree or severity of that pathogenicity.

What are the definitions of $ID_{50}$ and $LD_{50}$?

$ID_{50}$ is the number of pathogen cells/virions to cause infection in $50\%$ of test animals; $LD_{50}$ is the number/amount to kill $50\%$ of test animals.

What is Antigenic variation?

When a pathogen changes its surface proteins or molecules so that previously produced antibodies no longer recognize it.

Contrast Antigenic drift and Antigenic shift.

Antigenic drift involves small changes via point mutations; Antigenic shift involves major changes through reassortment of viral genes.

What are Mycotoxins?

Toxins produced by fungi that can damage cells, interfere with the nervous or immune systems, or cause cancer (e.g., aflatoxin).

Define Bacteremia and Septicemia.

Bacteremia is the presence of bacteria in the blood; Septicemia is the presence and active multiplication of bacteria in the blood.

What are Exoenzymes?

Enzymes released outside a pathogen's cell that help it invade tissues, spread, or escape host defenses (e.g., Hyaluronidase, Collagenase).

What is a Superantigen?

A toxin that overstimulates large numbers of immune cells, causing a massive release of inflammatory molecules that can lead to shock and organ failure.

What is a biofilm and its matrix composition?

An organized community of microorganisms attached to a surface, surrounded by a matrix of extracellular polymeric substances ($EPS$).

What are the five steps of biofilm formation?

1. Initial attachment; 2. Irreversible attachment; 3. Early maturation; 4. Mature biofilm; 5. Dispersion.

What is Quorum sensing?

Microbial communication based on population density using signaling molecules called autoinducers to coordinate group behavior.

How is total magnification calculated in light microscopy?

Total magnification equals Ocular magnification $10\times$ multiplied by Objective magnification ($4\times$, $10\times$, $40\times$, or $100\times$).

What are the two types of electron microscopes and what do they show?

Transmission electron microscope ($TEM$) shows internal structures through thin specimens; Scanning electron microscope ($SEM$) shows three-dimensional-looking surface details.

Define Basic dye and Acidic dye in staining.

A basic dye has a positively charged chromophore that stains negatively charged bacterial cells directly; an acidic dye has a negatively charged chromophore that stains the background.

List the four steps of Gram staining.

1. Primary stain (Crystal violet); 2. Mordant (Gram’s iodine); 3. Decolorizer (Alcohol/Acetone); 4. Counterstain (Safranin).

What is the purpose of an Acid-fast stain?

To identify bacteria with waxy mycolic acid in their cell walls, such as Mycobacterium tuberculosis, which retain the primary red stain.

Describe the Schaeffer-Fulton endospore staining method.

Heat is used to push malachite green into the endospore, water removes dye from the vegetative cell, and safranin stains the vegetative cell pink.

How is the DNA arranged in prokaryotic cells compared to eukaryotic cells?

In prokaryotes, DNA is sits in an area called the nucleoid without a nuclear membrane; in eukaryotes, DNA is inside a nuclear membrane within a nucleus.

Which groups of microorganisms are classified as prokaryotic and which are eukaryotic?

Bacteria and archaea are prokaryotic; fungi, protists, and helminths are eukaryotic.

What is the defining characteristic of a virus's cellular structure?

Viruses are acellular, meaning they are not cells; they consist of genetic material inside a protein coat.

What are plasmids in prokaryotic cells?

Extra pieces of DNA that can carry useful traits.

What is the size of ribosomes found in prokaryotic cells?

$$70S$$

What is the purpose of bacterial endospores?

They are for survival in harsh conditions, not for reproduction; they protect the DNA until conditions improve.

What are the main structural differences between the cell walls and membranes of Bacteria and Archaea?

Bacteria usually have cell walls with peptidoglycan, while Archaea do not; Archaea can also have different membrane structures.

Why do Gram-positive bacteria appear purple after Gram staining?

They have a thick peptidoglycan layer that holds onto the purple stain.

Why do Gram-negative bacteria appear pink/red after Gram staining?

They have a thinner peptidoglycan layer and an outer membrane; they lose the purple stain during decolorizing and take the counterstain.

What type of bacteria is detected using an Acid-fast stain?

Bacteria that have waxy mycolic acid in their cell walls.

How do capsules appear in a Capsule stain?

They show up as a clear halo around the cell because they do not absorb most dyes well.

In fungi, what is the difference between yeasts and molds?

Yeasts are unicellular fungi, while molds are multicellular fungi made of filaments called hyphae.

What unique components are found in fungal cell walls and membranes?

Fungal cell walls contain chitin, and their cell membranes contain ergosterols.

What are the two main groups of parasites discussed in microbiology?

Protists (specifically protozoa) and Helminths (parasitic worms).

In the life cycle of a protozoan, what is the difference between a trophozoite and a cyst?

A trophozoite is the active feeding stage; a cyst is a protective form used when conditions are harsh.

What is the difference between pathogenicity and virulence?

Pathogenicity is the ability to cause disease; virulence is the measure of how severe or harmful the pathogen is.

What is an opportunistic pathogen?

A normally harmless microbe that causes disease if it enters the wrong body area or if the host's defenses are weakened.

What are adhesins?

Virulence factors that help pathogens stick to host cells.

What is antigenic variation?

A strategy where a pathogen changes its surface proteins so the immune system has a harder time recognizing it.

What is the difference between endotoxins and exotoxins?

Exotoxins are toxins released by pathogens; endotoxins are part of the outer membrane (LPS) of gram-negative bacteria.

How do exoenzymes assist pathogens?

They are released by pathogens to break down barriers like connective tissue or membranes, helping the pathogen invade and spread.

What is nitrogen fixation and which organisms perform it?

The process of turning atmospheric nitrogen into ammonia for plants; it is done only by prokaryotes.

What is bioremediation?

The use of microbial metabolism to clean up pollution or contaminated environments.

What is the difference between synthetic and semisynthetic antimicrobials?

Synthetic antimicrobials are fully man-made; semisynthetic start as natural substances but are chemically changed to work better.

In gene therapy, what is the role of a vector?

A carrier, usually a virus, used to deliver a corrected gene into the host's cells.

What is the purpose of oil immersion in light microscopy?

It helps improve resolution at high magnification by reducing light scattering.

What are the specific uses of TEM and SEM in electron microscopy?

TEM (Transmission Electron Microscope) is used to see internal structures; SEM (Scanning Electron Microscope) is used to see surface structures.