Microbial Cell Structure and Function

Vocabulary flashcards created from lecture notes on bacterial cell structures, envelopes, inclusions, and morphological features.

Coccus

A spherical or round-shaped bacterial cell.

Diplococcus

Pairs of cocci cells.

Streptococcus

Twisted chains of cocci cells.

Staphylococcus

Grape-like clusters of cocci cells.

Tetrad

An arrangement of 4 cocci forming a square.

Bacillus

A rod-shaped bacterial cell.

Vibrio

A curved rod-shaped bacterial cell.

Spirillum

A rigid, spiral-shaped (helix) bacterial cell.

Spirochete

A flexible, spiral-shaped (helix) bacterial cell.

Pleomorphic

Organisms that exhibit variable or inconsistent cell shapes.

Hyphae

Long filaments formed by some bacteria and many fungi.

Mycelium

A network of interconnected hyphae.

Thiomargarita

One of the largest known bacteria, measuring $>600\,\mu m$ and often referred to as sulfur pearl.

Surface-to-Volume Ratio (S/V Ratio)

A ratio that is higher in smaller cells, allowing for more efficient nutrient uptake and faster cell growth.

Bacterial Cell Envelope

The structural boundary surrounding the cell, composed of the plasma membrane, cell wall, and external layers outside the cell wall.

Plasma Membrane

A selectively permeable membrane encompassing the cytoplasm that functions as the main site of energy generation, transport systems, and signal transduction systems.

Fluid Mosaic Model

A structural model of membranes describing a lipid bilayer with floating proteins, where amphipathic lipids contain flexible ester bonds, hydrophilic polar heads, and hydrophobic non-polar tails.

Bacterial Cell Wall

A rigid structural layer located just outside the plasma membrane that determines cell shape and protects against toxic substances and osmotic lysis.

Osmotic Lysis

Cell rupture caused by movement of water into the cell when placed in hypotonic solutions where $\text{[solute]}_{\text{outside cell}} < \text{[solute]}_{\text{inside cell}}$.

Gram-Positive Bacteria

Bacteria with cell walls containing thick, multiple layers of peptidoglycan and teichoic acids, which retain crystal violet and stain purple.

Gram-Negative Bacteria

Bacteria with cell walls containing a thin layer of peptidoglycan and an outer membrane composed of lipids, porins, and lipopolysaccharides, staining pink.

Peptidoglycan

A polysaccharide component of bacterial cell walls formed from alternating subunits of $N\text{-acetylglucosamine}$ (NAG) and $N\text{-acetylmuramic acid}$ (NAM) cross-linked by peptides.

Transpeptidation

The chemical reaction that forms peptide cross-links between peptidoglycan chains to provide cell wall strength.

Teichoic Acids

Sugar polymers present in Gram-positive cell walls that provide structural stability.

Lipopolysaccharide (LPS)

A molecule in the Gram-negative outer membrane consisting of Lipid A, core polysaccharide, and O side chain (O antigen); functions as an endotoxin.

Lipid A

The lipid component of lipopolysaccharide (LPS) anchored in the outer membrane that acts as the toxic component.

Endotoxin

A toxic cell-wall component (such as LPS) released when bacteria divide or lyse, capable of inducing fever and septic shock in a host.

Capsule

An organized polysaccharide layer outside the bacterial cell wall that is not easily removed and protects against desiccation and immune response.

Slime Layer

A diffuse, unorganized polysaccharide layer outside the cell wall that is easily washed away.

S Layer

An organized protein layer situated outside the cell wall that contributes to structural stability and surface protection.

Cytoplasm

A highly concentrated, mostly water-based internal matrix in which cellular inclusions, chromosomes, and ribosomes are suspended.

Poly-B-hydroxybutyrate (PHB) Granules

Carbon storage inclusions inside bacterial cytoplasm used commercially to manufacture biodegradable plastic.

Polyphosphate Granules

Metachromatic inclusions that store phosphate and sulfur reserves.

Cyanophycin Granules

Inclusions composed of amino acid chains that store nitrogen and carbon.

Gas Vacuoles

Cytoplasmic inclusions found in aquatic bacteria (such as cyanobacteria) that regulate buoyancy.

Magnetosomes

Inclusions containing magnetic particles ($25\text{--}125\,\text{nm}$ diameter) arranged in chains along MamK cytoskeletal filaments, enabling magnetotactic bacteria to orient in Earth's magnetic field.

Thylakoids

Infolded photosynthetic internal membranes containing chlorophyll found in cyanobacteria.

Carboxysomes

Polyhedral protein-shelled microcompartments in $\text{CO}_2$-fixing bacteria containing enzymes like RuBisCO for carbon fixation.

RuBisCO

An enzyme housed inside carboxysomes that adds $\text{CO}_2$ to Ribulose 1,5-bisphosphate (RuBP) as the first key step of the Calvin cycle.

Nucleoid

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

Plasmids

Small, closed circular DNA molecules in the cytoplasm that replicate independently of the bacterial chromosome.

R Plasmids

Plasmids carrying genes that confer antibiotic resistance to the host bacterium.