Microbiology: Cell Biology, Bacterial Cell Walls, and Microscopy

Comprehensive review flashcards covering bacterial cell wall architecture, membrane transport, microscope components and protocol, prokaryotic morphology and appendages, and eukaryotic organelle structure and endomembrane trafficking.

What structural difference distinguishes a saturated fatty acid from an unsaturated fatty acid?

A saturated fatty acid contains only single carbon-carbon bonds and maximum bonded hydrogens, while an unsaturated fatty acid contains one or more carbon-carbon double bonds that introduce kinks into the hydrocarbon chain.

What are the primary functions and physical properties of the bacterial cell membrane?

It acts as a selective barrier controlling what enters and exits the cell, serves as the site of bacterial energy production (respiration), and is fluid, flexible, and capable of self-repairing small breaks.

According to the membrane permeability model shown, which classes of molecules can directly diffuse across the phospholipid bilayer, and which are blocked?

Gases ($CO_2$, $O_2$), hydrophobic molecules (benzene), and small polar molecules ($H_2O$, ethanol) can diffuse across, whereas large polar molecules (glucose) and charged ions ($H^+$, $Na^+$, $Cl^-$, $Ca^{2+}$, amino acids) are blocked.

How is diffusion defined in cellular transport?

The movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached.

What physical process is depicted in this beaker setup showing solvent movement across a semipermeable membrane?

Osmosis, defined as the net movement of water (solvent) across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration.

What are the three major functions of the bacterial cell wall?

It is a semi-rigid structure responsible for maintaining the shape of the cell, prevents rupture of the cell due to internal water pressure, and serves as an anchorage point for flagella.

What two alternating amino sugars form the carbohydrate backbone of bacterial peptidoglycan?

$N\text{-acetylglucosamine}$ (NAG) and $N\text{-acetylmuramic acid}$ (NAM).

What amino acids compose the peptide side chains attached to NAM in E. coli peptidoglycan?

L-alanine, D-glutamic acid, Meso-diaminopimelic acid, D-alanine, and D-alanine.

What structural components characterize the Gram-positive cell wall shown in this diagram?

Several thick layers of peptidoglycan sheets anchored by Wall Teichoic Acid (WTA), which links peptidoglycan sheets together, and Lipoteichoic Acid (LTA), which links the peptidoglycan sheets to the plasma membrane.

What distinct structural features define the Gram-negative bacterial cell wall shown here?

A single thin layer of peptidoglycan situated in the periplasm between the plasma membrane and an asymmetric outer membrane covered in lipopolysaccharides (LPS) and porin proteins.

What are the three structural components of lipopolysaccharide (LPS), and which part is responsible for toxicity?

LPS consists of Lipid A, core polysaccharide, and O polysaccharide (O-antigen); Lipid A is the toxic component released when cleaved by the host immune system.

Why does lipopolysaccharide (LPS) prevent the entry of certain antibiotics into Gram-negative bacteria?

LPS is highly negatively charged, creating a selective chemical barrier that prevents the passage of various extracellular molecules, including certain antibiotics.

Why do Gram-positive cells retain the crystal violet stain while Gram-negative cells do not during the alcohol decolorization step?

In Gram-positive bacteria, the thick multilayered peptidoglycan wall traps the crystal violet-iodine complex, preventing it from washing out; in Gram-negative bacteria, the thin peptidoglycan layer fails to trap the complex, allowing alcohol to wash it out.

Identify the primary optical and mechanical components of the compound light microscope shown.

Ocular lens (eyepiece), diopter adjustment, nose piece, objective lenses, stage clips, aperture, diaphragm, condenser, illuminator (light source), head, arm (carrying handle), mechanical stage, coarse adjustment, fine adjustment, stage controls, base, brightness adjustment, and light switch.

How is total magnification calculated on a compound microscope, and what are the magnifications for scanning, low power, and high power objectives using a $10\text{x}$ ocular lens?

Total magnification is calculated by multiplying the ocular lens magnification by the objective lens magnification: Scanning is $10 \times 4 = 40\text{x}$, Low Power is $10 \times 10 = 100\text{x}$, and High Power is $10 \times 40 = 400\text{x}$.

What are the sequential steps for focusing an initial specimen on a compound light microscope?

1. Ensure the scanning objective is in place and stage is in the lowest position; 2. Place slide on stage and center the specimen; 3. Look through the eyepiece with both eyes; 4. Use the Coarse Focus Knob to bring the object into view; 5. Center the object and use the Fine Focus Knob to make it clear.

Which focus knob should be used when transitioning from the scanning objective to low power and high power objectives?

Only the fine adjustment knob should be used to refocus once moved past the scanning objective.

What are the mandatory care and handling rules for storing and moving a compound light microscope?

Always carry with 2 hands (one on the arm, one on the base), clean optics only with lens paper, do not force knobs, keep the desk and cords clear, and store with the scanning objective in place and the stage in the lowest position.

What are the six typical bacterial cell morphologies depicted in this diagram?

Coccus (spherical), Coccobacillus (intermediate oval), Vibrio (comma-shaped curved rod), Bacillus (rod-shaped), Spirillum (rigid spiral), and Spirochete (flexible helix).

What are the six common cellular arrangements of cocci shown here?

Coccus (single sphere), diplococci (pairs), staphylococci (grape-like clusters), streptococci (chains), sarcina (cubical packets of eight), and tetrad (groups of four).

What distinct arrangements can bacillus-shaped bacteria form?

Coccobacillus, single bacilli, diplobacilli (pairs), streptobacilli (chains), and palisades (side-by-side picket-fence arrangement).

What is a glycocalyx, and how do capsules differ from slime layers in prokaryotes?

A glycocalyx is an external sugar coat surrounding cells; a capsule is organized and firmly attached (protects against phagocytosis, aids biofilm adhesion, and prevents dehydration), whereas a slime layer is unorganized and loosely attached.

How do bacterial flagella generate cell motility?

Flagella are long filamentous appendages anchored across the cell wall that rotate clockwise and counterclockwise to produce 'running and tumbling' movements.

How does flagellar basal body attachment differ structurally between Gram-negative and Gram-positive bacteria?

A Gram-negative flagellum has a basal body containing two pairs of rings that anchor it across both the outer membrane and the plasma membrane, whereas a Gram-positive flagellum has a basal body containing a single pair of rings anchored solely into the plasma membrane.

What are fimbriae, and what is their primary function in prokaryotic cells?

Fimbriae are thick, tube-like, hair-like filaments that are smaller than flagella and often cover the entire cell surface; they function primarily in attaching the cell to surfaces or other objects.

What specialized bacterial structure is shown bridging these two cells, and what is its role?

A sex pilus (plural: pili), which is longer than fimbriae with typically only one or two present per cell, utilized to transfer DNA between bacterial cells during conjugation.

What is the prokaryotic nucleoid?

The nuclear region of a prokaryote containing a single, long, circular double-stranded DNA molecule (the bacterial chromosome) that carries all the essential genes required for cellular structure and function.

What are plasmids, and what specialized adaptive traits do they typically encode?

Plasmids are small, circular, extrachromosomal double-stranded DNA molecules that replicate independently of the bacterial chromosome, carrying $5\text{--}100$ genes that typically confer metal tolerance, toxin production, environmental enzymes, or antibiotic resistance.

What are bacterial inclusion bodies?

Reserve packets within the cytoplasm that store extra nutrients or materials that the bacterial cell can draw upon if environmental conditions change.

What is a bacterial endospore, and what conditions can it resist?

A specialized dehydrated dormant cell formed internally with a thick cell wall and protective 'spore coat' that contains a copy of the chromosome; it released upon exposure to hostile environments and is highly resistant to heat, dehydration, toxic chemicals, and radiation.

According to this biological scale, what are the characteristic size ranges for DNA, viruses, prokaryotic cells, and eukaryotic cells?

DNA is approximately $2\,\text{nm}$, cold viruses are approximately $25\,\text{nm}$, typical prokaryotic cells measure $1\text{--}5\,\mu\text{m}$, and typical eukaryotic cells measure $10\text{--}100\,\mu\text{m}$.

Based on this comparative cell diagram, which organelles are exclusively identified in plant cells versus animal cells?

Chloroplasts, a central vacuole, and a cell wall are shown exclusively in plant cells, whereas centrioles and lysosomes (or lytic vacuoles in plants) are labeled as animal-specific structures.

How do eukaryotic cell walls differ chemically from bacterial cell walls?

Eukaryotic cell walls are structurally simpler and made of cellulose in plants and algae or chitin in fungi; eukaryotic cells never contain peptidoglycan.

What are the structure and functions of the eukaryotic glycocalyx?

A layer of carbohydrates, glycoproteins, and glycolipids covering the plasma membrane that functions to strengthen the cell surface, facilitate cell-to-cell adhesion, and contribute to cell-cell recognition.

How do eukaryotic flagella and cilia differ in number, length, and movement from prokaryotic flagella?

Eukaryotic flagella are few and long relative to cell size, while cilia are numerous and short; both are anchored to the plasma membrane and move in a wavelike undulating motion, unlike the rotating propeller motion of prokaryotic flagella.

What three types of eukaryotic endocytosis are shown in this diagram, and how do they function?

Phagocytosis (engulfment of solid particles by pseudopodia into phagosomes), pinocytosis (inward folding of the membrane to drink extracellular fluid into vesicles), and receptor-mediated endocytosis (selective uptake of specific ligands bound to membrane receptors into coated pits and coated vesicles).

What internal structures comprise the eukaryotic nucleus?

The nuclear envelope with nuclear pores that regulate transport, chromatin (DNA wrapped around histone proteins), the nucleoplasm, and the nucleolus where ribosomes are produced.

What are the structural compartments and primary function of the mitochondrion shown here?

It consists of an outer membrane, an inner membrane folded into cristae to maximize surface area, and an internal central matrix; it serves as the cellular site of ATP production.

How do prokaryotic and eukaryotic ribosomes differ in their overall sedimentation coefficients and subunit compositions?

Ribosomes are where proteins are made in the cell and participate in RNA synthesis, using the amino acid sequence. Prokaryotic ribosomes (70s) are free-floating in the cytoplasm and consist of 2 subunits of RNA and protein.

What functional differences distinguish the rough endoplasmic reticulum from the smooth endoplasmic reticulum?

The rough ER is studded with ribosomes and synthesizes proteins destined for membranes or secretion, while the smooth ER lacks ribosomes and synthesizes phospholipids, fats, and steroids, and mediates post-translational modifications like glycosylation.

What pathway do newly synthesized proteins follow through the endomembrane system as illustrated?

Proteins synthesized on ribosomes bound to the rough ER are packaged into transport vesicles, fuse with the cis face of the Golgi apparatus cisternae for modification and sorting, and exit from the trans face via secretory vesicles to be expelled from the cell membrane.

How do lysosomes differ from peroxisomes in origin and catalytic function?

Lysosomes are formed from Golgi complexes, surrounded by a single membrane, and contain digestive enzymes to break down bacteria and cellular debris; peroxisomes contain specific enzymes that modify organic molecules, oxidize fatty acids (lipid metabolism), and convert toxic hydrogen peroxide ($H_2O_2$).

What are the differences in prokaryote and eukaryote cells?

Prokaryotes lack a membrane-bound nucleus and keep their single circular chromosome in an unbound nucleoid region (often with plasmids), whereas eukaryotes possess a true membrane-bound nucleus containing linear chromatin (DNA wrapped around histones) and a nucleolus.