Bacterial Cell Structure

Vocabulary flashcards covering bacterial cell shapes, cell envelope components, membrane transport systems, cytoplasmic inclusions, and external structures based on Chapter 3 of Prescott's Microbiology.

Diplococci

Spherical bacterial cells that occur in pairs.

Streptococcus

Spherical bacterial cells arranged in chains.

Staphylococcus

Spherical bacterial cells arranged in grapelike clusters.

Sarcina

A cubic packet consisting of 8 spherical bacterial cells.

Coccobacilli

Short and wide rod-shaped bacteria.

Vibrios

Comma-shaped bacterial cells.

Spirochetes

Flexible, spiral-shaped bacteria.

Pleomorphic

Organisms that are naturally variable in shape.

Cell envelope

The plasma membrane and all surrounding layers external to it, including the cell wall, capsule, or slime layer.

Amphipathic lipids

Structurally asymmetric lipids containing polar hydrophilic ends that interact with water and nonpolar hydrophobic ends that associate with each other.

Peripheral membrane proteins

Proteins loosely connected to the membrane that are easily removed and constitute $20$ to $30\%$ of total membrane proteins.

Integral membrane proteins

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

Hopanoids

Hydrophobic molecules similar to cholesterol that distort the lipid bilayer, impact membrane fluidity and shape, and form functional microdomains for protein complex assembly.

Growth factors

Organic compounds essential for bacterial survival that the cell cannot synthesize and must obtain from the environment.

Siderophores

Organic molecules secreted by microorganisms when iron levels are low to bind ferric ions ($\text{Fe}^{3+}$) for cellular transport.

ATP-Binding Cassette (ABC) Transporters

Primary active transport systems that utilize energy from ATP hydrolysis to import molecules via ATP-binding and membrane-spanning domains.

Symport

A secondary active transport mechanism in which two ions or substances move across the membrane in the same direction.

Antiport

A secondary active transport mechanism in which two ions or substances move across the membrane in opposite directions.

Group translocation

An energy-dependent transport process that chemically modifies a substance, such as phosphorylating sugars via the phosphotransferase system (PTS), as it is brought into the cell.

Monoderm

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

Diderm

A bacterial cell envelope containing both a plasma membrane and an outer membrane with a thin peptidoglycan layer in between, characteristic of Gram-negative bacteria.

Teichoic acids

Negatively charged glycerol polymers in Gram-positive cell walls that help maintain the cell envelope, protect from environmental stresses, aid in iron uptake, and bind host cells.

Lipid A

The glucosamine derivative and fatty acid portion of lipopolysaccharide (LPS) that anchors it in the outer membrane and acts as an endotoxin.

O antigen

The polysaccharide portion of lipopolysaccharide (LPS) extending outward from the core that functions in host defense protection.

Porins

Channel proteins located in the outer membrane of Gram-negative bacteria that allow nutrients and small molecules up to $600\text{ daltons}$ to pass into the periplasm.

Plasmolysis

The shrinkage of the cytoplasm away from the cell wall caused by water loss when a cell is in a hypertonic environment.

Capsule

A well-organized polysaccharide layer covalently bonded to the cell that is not easily removed and protects against phagocytosis, desiccation, viruses, and detergents.

Slime layer

A diffuse, unorganized polysaccharide layer external to the cell wall that is easily washed away and may facilitate cell motility.

FtsZ

A bacterial tubulin homologue that forms a ring at the center of a dividing cell that constricts as daughter cells separate.

MreB

A bacterial actin homologue that maintains rod shape by positioning peptidoglycan synthesis machinery.

CreS

An intermediate filament homologue in bacteria that maintains curved cell shape.

Carboxysomes

Microcompartments in $\text{CO}_2$-fixing bacteria containing carbonic anhydrase and RuBisCO to accumulate high concentrations of carbon dioxide for sugar synthesis.

Magnetosomes

Intracellular inclusions made of magnetite ($\text{Fe}_3\text{O}_4$) or greigite ($\text{Fe}_3\text{S}_4$) organized by MamK that allow aquatic bacteria to orient along Earth's magnetic field.

70S Ribosome

The bacterial and archaeal protein synthesis complex consisting of a 30S small subunit (with 16S rRNA) and a 50S large subunit (with 23S and 5S rRNA).

Episomes

Plasmids capable of integrating into the host bacterial chromosome and replicating synchronously with it.

Sex pili

Long, thick, genetically encoded plasmid appendages (approximately 10 per cell) required for bacterial conjugation.

Flagellar basal body

The motor component of the bacterial flagellum embedded within the cell envelope layers.

Sporulation

The multi-step process by which a vegetative bacterial cell forms a dormant, highly resistant endospore in response to nutrient depletion.