Prescott's Microbiology Chapter 3: Bacterial Cell Structure

Vocabulary flashcards covering key definitions, terms, structural features, and functional processes of bacterial cells from Chapter 3.

Norman Pace (2006 Proposal)

Stated in 2006 that the term "prokaryote" should be abandoned based on biochemical, genetic, and genomic evidence showing Bacteria and Archaea are distinct.

Cocci

Spherical bacterial cells.

Diplococci

Spherical bacterial cells that divide and remain in pairs.

Streptococci

Spherical bacterial cells that divide on a single plane to form chains.

Staphylococci

Spherical bacterial cells that divide in random planes, forming grape-like clusters.

Tetrads

Spherical bacterial cells that divide in $2$ planes, forming a square arrangement of $4$ cocci.

Sarcina

Spherical bacterial cells that divide in $3$ planes, making a cubic packet of $8$ cocci.

Bacilli

Rod-shaped bacterial cells.

Coccobacilli

Short and wide rod-shaped bacterial cells.

Vibrios

Comma-shaped bacterial cells.

Spirilla

Rigid spiral-shaped bacterial cells.

Spirochetes

Flexible spiral-shaped bacterial cells.

Mycelium

A network of long filaments called hyphae formed by certain bacteria.

Pleomorphic

Term describing organisms that are variable in cell shape.

Cell Envelope

The plasma membrane and all of the surrounding structural layers external to it.

Amphipathic Lipids

Lipids possessing hydrophilic polar ends that interact with water and hydrophobic non-polar tails that are insoluble in water.

Peripheral Membrane Proteins

Proteins loosely connected to the membrane that account for $20$ to $30$ percent of total membrane proteins and are easily removed.

Integral Membrane Proteins

Amphipathic proteins embedded within the lipid bilayer that are not easily removed and perform functions such as transport.

Hopanoids

Hydrophobic lipid molecules similar to cholesterol that distort the membrane bilayer, impacting fluidity and forming functional membrane microdomains.

Macronutrients

Nutrients required by cells in large amounts, including carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium, and iron.

Micronutrients

Trace elements required in small amounts (such as manganese, zinc, cobalt, molybdenum, nickel, and copper) that assist enzyme catalysis and maintain protein structure.

Growth Factors

Organic compounds required for survival (such as amino acids, purines, pyrimidines, and vitamins) that a cell cannot synthesize and must obtain from the environment.

Passive Diffusion

Movement of molecules across a membrane from higher to lower concentration without energy or transport proteins, as seen with $\text{H}_2\text{O}$, $\text{O}_2$, and $\text{CO}_2$.

Facilitated Diffusion

Energy-independent transport of molecules across the plasma membrane down a concentration gradient using channel or carrier proteins.

Active Transport

Energy-dependent transport of molecules against a concentration gradient using ATP or proton motive force.

ABC Transporters

ATP-binding cassette primary active transporters consisting of $2$ hydrophobic membrane-spanning domains and $2$ cytoplasmic ATP-binding domains.

Symport

Secondary active transport mechanism where $2$ substances move across the membrane in the same direction.

Antiport

Secondary active transport mechanism where $2$ substances move across the membrane in opposite directions.

Group Translocation

An energy-dependent transport process that chemically modifies a molecule as it is brought into the cell, such as the phosphoenolpyruvate: sugar phosphotransferase system (PTS).

Siderophores

Molecules secreted by microorganisms that complex with ferric iron to enable its transport into the cell.

Peptidoglycan

A rigid meshlike polymer of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) sugars cross-linked by amino acids, located outside the plasma membrane.

Monoderm

A bacterial cell envelope structure consisting of a single membrane surrounded by a thick peptidoglycan layer, characteristic of Gram-positive bacteria.

Diderm

A bacterial cell envelope structure consisting of a plasma membrane and an outer membrane surrounding a thin peptidoglycan layer, characteristic of Gram-negative bacteria.

Teichoic Acids

Negatively charged polymers of glycerol present in Gram-positive cell walls that help maintain the cell envelope and protect against environmental substances.

Braun's Lipoproteins

Lipoproteins in Gram-negative bacteria that connect the outer membrane to the underlying peptidoglycan layer.

Lipopolysaccharide (LPS)

A major outer membrane component of Gram-negative bacteria consisting of Lipid A, core polysaccharide, and an O side chain (O antigen).

Porins

Transmembrane proteins in Gram-negative outer membranes that form channels allowing small molecules up to $600\,\text{daltons}$ to pass.

Plasmolysis

The shrinkage of the cytoplasm away from the cell wall when a cell is placed in a hypertonic environment.

Protoplast

A Gram-positive cell that completely lacks a cell wall when placed in an isotonic environment.

Spheroplast

A cell that loses its peptidoglycan layer but retains its outer membrane when treated in an isotonic environment.

Extracellular Vesicles (EVs)

Small non-replicating membrane-bound particles ($20$ to $400\,\text{nm}$) that bud off from bacterial membranes to carry materials and facilitate cell-cell interactions.

Capsules

Well-organized polysaccharide layers covalently bonded to the cell envelope that resist phagocytosis and exclude viruses and detergents.

Slime Layers

Diffuse, unorganized polysaccharide layers surrounding bacterial cells that are easily washed away and may facilitate motility.

Glycocalyx

A polysaccharide extension from the cell envelope that aids in attachment to solid surfaces.

S-Layers

Regularly structured, self-assembling protein or glycoprotein layers outside the cell wall that protect against ion/pH fluctuations, osmotic stress, and predation.

FtsZ

A bacterial cytoskeletal protein homolog that forms a ring at the center of a dividing cell to constrict the cell during division.

MreB

A bacterial cytoskeletal protein homolog found in rod-shaped bacteria that maintains cell shape by positioning peptidoglycan synthesis machinery.

CreS

A bacterial cytoskeletal protein homolog responsible for maintaining a curved cell shape.

Inclusions

Aggregates of organic or inorganic substances (granules, crystals, or globules) stored in the cytoplasm for future use or to sequester cellular components.

Carboxysomes

Microcompartments in $\text{CO}_2$-fixing bacteria containing carbonic anhydrase and RuBisCO for sugar production.

Gas Vacuoles

Inclusions composed of aggregates of hollow, cylindrical gas vesicles that provide buoyancy to aquatic bacteria.

Magnetosomes

Inclusions found in aquatic bacteria containing magnetite particles that align cells along Earth's magnetic field via the cytoskeletal protein MamK.

70S Ribosome

The bacterial ribosome complex consisting of a $30S$ small subunit (containing $16S$ rRNA) and a $50S$ large subunit (containing $23S$ and $5S$ rRNA).

Nucleoid

The non-membrane-bound region in bacterial cells containing the chromosome, typically a single closed circular double-stranded DNA molecule.

Plasmids

Small, extrachromosomal closed circular DNA molecules that replicate independently of the chromosome and carry genes conferring selective advantages.

Fimbriae

Short, thin, hairlike protein appendages (up to $1000$ per cell) that mediate surface attachment, motility, and DNA uptake.

Sex Pili

Longer, thicker, and less numerous hair-like appendages ($10$ per cell) encoded on plasmids that are required for bacterial conjugation.

Monotrichous

A flagellar distribution pattern characterized by a single flagellum.

Amphitrichous

A flagellar distribution pattern characterized by a single flagellum at each end of the cell.

Lophotrichous

A flagellar distribution pattern characterized by a cluster of flagella at one or both ends of the cell.

Peritrichous

A flagellar distribution pattern where flagella are spread randomly over the entire cell surface.

Swarming

Group motility across moist surfaces performed by bacteria typically possessing peritrichous flagella and producing surface tension-lowering molecules.

Twitching Motility

Short, intermittent, jerky surface movements mediated by Type IV pili at the ends of cells.

Chemotaxis

Directional cell movement toward a chemical attractant or away from a chemical repellent.

Bacterial Endospore

A complex, dormant cell structure produced in response to nutrient depletion that is highly resistant to heat, UV radiation, desiccation, and chemicals.

Sporulation

The multi-stage process of endospore formation triggered by nutrient lack or slowing growth.