Microbiology - Ch. 4 Prokaryotic and Eukaryotic Cell Anatomy - flashcards (CONDENSED)

Why do we need to know the average size of bacterial cells, and what unit is it measured in?

For identification purposes. Measured in microns (µm).

What is an example average size for a bacterial cell?

~2.0 µm diameter × ~8 µm length.

What is the difference between monomorphic and pleomorphic bacteria?

• Monomorphic: one shape present in the visual field; all bacteria are identical (e.g., all round, or all rod-shaped)

• Pleomorphic: several shapes present in the visual field; more than one bacterial shape type present

What are the 3 basic bacterial cell shapes?

• Coccus = round/spherical

• Bacillus = rod-shaped (coccobacillus = "oval" shaped)

• Spiral = 3 types (vibrio, spirillum, spirochete)

What are the 3 types of spiral bacteria, and what do they have in common?

• Vibrio = "comma" shaped

• Spirillum

• Spirochete

• All spiral types are motile

What is the difference between spirilla (singular: spirillum) and spirochetes?

• Spirilla: rigid, short/thick, loosely-coiled cells; move via flagella (external flagella).

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• Spirochetes: flexible, longer/thin, tightly-coiled cells; move via endoflagella ("internal" flagella — located inside the bacterium).

What are the cell arrangement prefixes for pairs, clusters, and chains, and what are they called?

• Pairs = "diplo-" → diplococci, diplobacilli

• Clusters = "staphylo-" → staphylococci

• Chains = "strepto-" → streptococci, streptobacilli

What are tetrads and Sarcinae?

• Tetrads = groups of 4 (cocci only)

• Sarcinae = cube-like groups of 8 (2 stacked tetrad layers)

For some bacteria, how is the genus name formed, and what's an example?

Genus name = arrangement + shape. Ex: Streptococcus pneumoniae → "Streptococcus" (arrangement) + "pneumoniae" (shape descriptor).

Glycocalyx — location, description, composition, and types?

• Location: layer external to the cell wall; surrounds the bacterium (secreted by some bacteria; may or may not be present — optional)

• Description: viscous, gelatinous, sticky

• Composition: polysaccharide or polypeptide

• Two types:

  • Capsule — made of polysaccharide (carb); thick, organized, tightly attached to cell wall

  • Slime layer — made of polypeptide (protein); thin, unorganized, loosely attached to cell wall

What is the function of a capsule?

• Bacterium attaches to host tissue due to "stickiness" of capsule (because it's carbohydrate)

• Makes bacterium look bigger → escapes phagocytosis (bacterial engulfment), since capsules are thick

What are two examples of encapsulated bacteria, and what's notable about each?

• Streptococcus mutans — present in mouth/teeth

• Streptococcus pneumoniae — causes pneumonia; has huge capsules

Flagella — location, function, and composition?

• Location: filamentous appendages external to the cell (may or may not be present)

• Function: movement/propel bacteria — helps find nutrient source and escape phagocytosis

• Composition: made of protein called flagellin

  • Flagellin proteins arrange into filaments; many filaments make up a flagellum (many types exist)

  • Can act as "H antigens" — help distinguish among different subspecies/strains of bacteria

  • Ex: Escherichia coli O157:H7 (H7 = a specific H antigen subspecies)

What exactly is an "H antigen," and what does the E. coli O157:H7 example show?

• One flagellin protein = "H antigen" (acts as a "surface marker")

• Flagellin proteins → filaments → flagellum

• Ex: H7 antigen is found in E. coli O157:H7, a pathogenic strain of E. coli

What are the three parts of a flagellum, and their functions?

1. Filament — outermost region

2. Hook — attaches to (joins) the filament to the basal body

3. Basal body — anchors the flagellum

Which bacteria may have flagella?

Found in some bacilli, and in all spirilla-type bacteria (unlike spirochetes, which move via endoflagella instead).

Axial filaments (endoflagella) — where found, location, composition, and function?

• Found in: spirochetes (vs. flagella in spirilla); may or may not be present

• AKA: endoflagella

• Location: internal to the cell (intracellular), within the cell wall; anchored at one end

• Composition: made of proteins

• Function: rotation of endoflagella → cell moves in corkscrew/spiral motion (motility)

Fimbriae — location, composition, description/function?

• Location: external to cell

• Composition: made of proteins

• Description/Function: hair-like appendages that allow for attachment

Pili — location, composition, function?

• Location: external to cell

• Composition: made of proteins

• Function: involved in "twitching" motility, and DNA transfer from one cell to another (ex: conjugation pilus — used for DNA/gene transfer from one cell to another)

How does conjugation via pilus work?

A pilus connects a donor cell to a recipient cell, transferring DNA from the donor into the recipient. The recipient cell then has inserted DNA from another bacterium — making the recipient cell now different (genetically altered).

Cell wall — location, function, composition?

• Location: outermost layer if no glycocalyx (capsule) present; most bacteria have a cell wall

• Function: prevents osmotic lysis and protects the cell membrane

• Composition: contains peptidoglycan (rows of carbohydrates connected to proteins)

What is the difference between Gram-positive and Gram-negative bacteria (peptidoglycan amount and stain color)?

• Gram-positive: more peptidoglycan (thick layer) → stains purple

• Gram-negative: less peptidoglycan (thin layer) → stains red/pink

What are the structural differences between Gram-negative and Gram-positive cell walls (layers, from outside in)?

• Gram-negative: has an outer membrane with lipopolysaccharide (LPS), then a thin peptidoglycan layer, then cytoplasmic membrane. Stains red/pink.

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• Gram-positive: no outer membrane/LPS — has a thick peptidoglycan layer directly outside the cytoplasmic membrane. Stains purple.

Compare Gram-positive vs Gram-negative cell walls in terms of teichoic acids and Penicillin sensitivity.

• Gram-positive: has teichoic acids; no outer membrane; sensitive to Penicillin (PCN destroys Gram+ bacteria)

• Gram-negative: no teichoic acids; has outer membrane with LPS; resistant to Penicillin (not destroyed by PCN)

What is LPS, where is it located, and what does it contain?

LPS (lipopolysaccharide) is the major component of the outer membrane of the Gram-negative cell wall, attached to the cell wall's outer membrane. Contains lipids & carbohydrates.

What are the 3 components of LPS, and their functions?

1. Lipid A — embedded into cell wall's outer membrane; functions as a toxin

2. Core polysaccharide — joins Lipid A & O polysaccharide

3. O polysaccharide — sticks out; functions as an antigen ("O antigen," acts as a surface marker); helps distinguish between subspecies/strains (ex: E. coli O157:H7 — "O157" = O polysaccharide)

What is Gram staining, and what does it target?

A differential stain used to classify/identify bacteria; stains the cell wall containing peptidoglycan.

What are the 4 steps of the Gram stain procedure?

1. Crystal violet (purple dye) — all cells start off purple/violet

2. Iodine (mordant) — rinse with H₂O

3. Alcohol wash (decolorization) — rinse; Gram-positive cell walls keep the purple dye, Gram-negative do not

4. Safranin (counterstain) — rinse; Gram-positive appears purple/violet, Gram-negative appears red/pink

Gram staining is used for identifying bacteria based on what 4 characteristics?

1. Gram reaction (+/-)

2. Shape

3. Arrangement

4. Size

What is atypical about the genus Mycobacterium's cell wall, and how is it stained?

Has a waxy lipid (mycolic acid) "bound" to peptidoglycan, present in the cell wall outer membrane — mycolic acid prevents digestion of the bacterium by phagocytosis (phagocyte engulfs it but doesn't destroy it). Uses acid-fast stain instead of Gram stain.

What is atypical about genus Mycoplasma and Domain Archaea cell walls?

• Mycoplasma: lacks cell walls entirely

• Domain Archaea: no peptidoglycan present in cell wall

Plasma (cell) membrane — location, composition, and characteristics?

• Location: deep to the cell wall

• Composition: phospholipid bilayer that encloses the cytoplasm

• Characteristics:

  • Peripheral proteins on the membrane surface

  • Integral & transmembrane proteins penetrate the cell membrane

What are the 3 functions of the plasma (cell) membrane in bacteria?

1. Transport — allows passage of some molecules but not others across the cell membrane ("selective permeability")

2. Site of ATP production — because bacteria have no mitochondria

3. Site of photosynthesis — because bacteria have no chloroplasts (only possible in certain bacteria)

What is passive transport, and does it require energy?

Movement of particles from an area of high → low concentration (includes simple diffusion and facilitated diffusion). Does not require energy.

What is active transport, and does it require energy?

Movement of particles from an area of low → high concentration. Requires energy (ATP).

What is the difference between simple diffusion and facilitated diffusion?

• Simple diffusion: movement of small, uncharged particles across the cell membrane (no protein needed)

• Facilitated diffusion: movement of large, charged particles across the cell membrane; particles require a protein channel or carrier

What is osmosis, and what direction does water move?

Movement of H₂O across a membrane; requires a concentration difference. Water moves toward the area of high concentration of particles.

Define isotonic, hypotonic, and hypertonic solutions, and their effect on the cell.

• Isotonic: same concentration of particles inside & outside the cell → no net H₂O movement

• Hypotonic: low particle concentration outside the cell → H₂O enters → cell swells

• Hypertonic: high particle concentration outside the cell → H₂O leaves → cell shrinks

In osmosis, which side is the "hypotonic environment" and which is "hypertonic," relative to water and solute movement?

H₂O moves from low solute concentration (hypotonic environment) → high solute concentration (hypertonic environment), across a semi-permeable membrane. (Water moves toward higher solute concentration; solute particles are more concentrated on the hypertonic side.)

Cytoplasm — location and composition?

The substance inside the plasma membrane; 80% water plus proteins, carbohydrates, lipids & ions. No organelles present, except for ribosomes.

Bacterial ribosomes — description, function, composition?

• Called 70S ribosomes (vs. Eukaryotic ribosomes, which are 80S)

• Description: not surrounded by a membrane (non-membrane bound)

• Function: sites of protein synthesis

• Composition: composed of 2 subunits — large subunit & small subunit

Nucleoid — description and composition?

"Nucleus-like" region (vs. nucleus in Eukaryotes); contains the bacterial chromosome — a circular thread of DNA, supercoiled/compacted, containing most of the cell's genetic information; NOT surrounded by a nuclear membrane.

Plasmid — description and function?

Small, circular, extrachromosomal genetic material, in addition to the nucleoid. Carries "non-crucial" genes that play a role in adaptability & survival (ex: genes for antibiotic resistance & production of toxins).

Inclusion bodies — description/location?

AKA reserve deposits; structures that store reserve materials in the cytoplasm.

What are the 4 examples of inclusion bodies and what does each store?

1. Metachromatic granules — phosphate reserves/storage

2. Polysaccharide granules — energy reserves of glycogen (polysaccharide)

3. Lipid inclusions — energy reserves of fat

4. Carboxysomes — enzyme reserves involved in photosynthesis

Endospores — location, description, and function?

• Location: formed inside the cell ("endospore"); if released outside the cell, called an "exospore"

• Description: specialized "resting"/dormant form of cells, seen in only a few bacteria; produced by Genus Bacillus and Genus Clostridium ("spore formers")

• Misc: produced when nutrients are depleted, for survival (adaptation)

• Function: contain the bacterial cell's genetic material (DNA)

• Misc: resistant to desiccation, heat, chemicals, and radiation — very tolerant; very dangerous since bacteria will become active once activated

What is the difference between sporulation and germination?

• Sporulation: endospore formation (becomes a spore; resting cell state)

• Germination: endospore returns to active cell state (becomes an active cell)

What triggers sporulation vs. germination, and what happens in each?

• Sporulation: occurs if low nutrients; active cell → forms an endospore (resting/dormant cell state); the cell eventually splits into an active cell + (exo)spore

• Germination: occurs if high nutrients; endospore → returns to active cell state

Compare Prokaryotic vs. Eukaryotic cells: chromosome, organelles, ribosomes, cell wall, and division.

• Prokaryote: one circular chromosome (not in a membrane); no organelles (except ribosomes); 70S ribosomes; peptidoglycan in cell walls; unicellular; divides by binary fission

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• Eukaryote: paired chromosomes in a nuclear membrane; membrane-bound organelles; 80S ribosomes; polysaccharide in cell walls (if present); unicellular & multicellular; divides by mitosis

Eukaryotic cell wall — where found, composition, and function?

• Found in: plants, algae (Kingdom Protista), and fungi

• Composition: made of carbohydrates — cellulose (in plants), chitin (in fungi)

• Function: structure and protection of the cell

Eukaryotic cell membrane — key features?

• Has sterols (a type of steroid) bound to the cell membrane

• Has carbohydrates — for attachment and cell-to-cell recognition

• Capable of endocytosis

What is the difference between phagocytosis and pinocytosis?

• Phagocytosis: engulfing particles

• Pinocytosis: engulfing fluids and dissolved substances

What are Eukaryotic ribosomes called, and what is their function?

80S ribosomes; site of protein synthesis.

Nucleus — structure and function?

Double membrane structure (nuclear envelope) that contains the cell's DNA.

What is the difference between Rough ER and Smooth ER?

• Rough ER: studded with ribosomes; sites of protein synthesis

• Smooth ER: no ribosomes; site of cell membrane, fat, and hormone synthesis

• Both form a folded transport network

What is the function of the Golgi Complex?

Modifies, sorts & packages proteins from the ER.

Lysosomes — origin and function?

Vesicles formed by the Golgi Complex; contain digestive enzymes.

Vacuoles — origin and function?

Cavities in the cell formed by the Golgi complex; bring food into cells and provide storage.

Mitochondria — structure and function?

Double membrane; contain inner folds (cristae) and fluid (matrix); involved in cellular respiration (ATP production).

Chloroplasts — structure and function?

Locations for photosynthesis; contain flattened membranes that contain chlorophyll pigment.

Centrosomes — function?

Form the mitotic spindle; critical role in cell division.