Microbial Cell Structure and Function

Vocabulary flashcards covering bacterial and archaeal cell structures, membrane transport, external appendages, and motility mechanisms.

Cytoplasmic Membrane

A selective permeability barrier and phospholipid bilayer that separates the cytoplasm from the environment and conserves energy through an $H^+$ gradient.

Unit Membrane

A term for the phospholipid bilayer where each phospholipid leaf forms half of the unit.

Sterols

Membrane strengthening agents found in Eukarya; they are generally absent in prokaryotes except for methanotrophic bacteria and mycoplasmas.

Hopanoids

Structural analogs of sterols found in the membranes of many Bacteria that serve to stabilize the structure and reduce flexibility.

Ether bonds

The type of chemical linkage found in Archaeal lipids between glycerol and their hydrophobic side chains, replacing the ester linkages found in Bacteria and Eukarya.

Isoprene

The five-carbon hydrocarbon repeating unit that forms the hydrophobic side chains of Archaeal lipids.

Phytanyl group

A $20$-carbon side chain found in Archaeal glycerol diethers.

Lipid Monolayer

A membrane structure formed by diglycerol tetraethers ($40$-carbon side chains) in some Archaea which is extremely resistant to heat denaturation.

Crenarchaeol

A major lipid of Crenarchaeota containing $5$- and $6$-carbon rings.

Simple Transport

A transport system, such as Lac permease in Escherichia coli, that uses energy from the proton motive force to accumulate substances against a concentration gradient.

Group Translocation

A form of transport where the substance is chemically modified (such as phosphorylation) during its uptake across the membrane.

Phosphotransferase System

A group translocation system in E. coli that transports glucose, mannose, and fructose using energy from phosphoenolpyruvate.

ABC Transport System

ATP-binding cassette systems consisting of periplasmic binding proteins, a membrane transporter, and an ATP-hydrolyzing protein.

Periplasmic Binding Proteins

Proteins in the periplasm with high substrate affinity (binding at less than $1 \times 10^{-6} M$) that interact with membrane transporters in ABC systems.

Capsule

An organized polysaccharide or protein layer that adheres firmly to the cell wall and assists in surface attachment and resistance to phagocytosis.

Slime Layer

An unorganized layer of polysaccharide or protein loosely attached to the cell wall that can be easily lost from the cell surface.

Biofilm

A thick layer of microorganisms bound to a solid surface.

Fimbriae

Short, numerous protein filaments that enable cells to stick to surfaces or animal tissues.

Pili

Long filamentous structures (typically only one or a few per cell) used for conjugation and adhesion to host tissues.

Type IV Pili

Specific pili ($6 nm$ in diameter) that allow for twitching motility through extension and retraction fueled by ATP.

Twitching Motility

A type of gliding motility where a cell moves along a solid surface via the extension and retraction of Type IV pili.

Flagellin

The protein that composes the helical filament of the bacterial flagellum.

Polar / Monotrichous

A flagellar arrangement featuring a single flagellum at one pole.

Lophotrichous

A flagellar arrangement featuring a tuft of flagella at one pole.

Amphitrichous

A flagellar arrangement with flagella at both poles.

Peritrichous

A flagellar arrangement where flagella are distributed all over the cell surface.

Mot Proteins

Proteins anchored in the cytoplasmic membrane that act as the 'stator' and conduct protons to drive flagellar rotation.

Fli Proteins

Proteins that function as the motor switch, reversing flagellar rotation direction in response to intracellular signals.

Proton Motive Force

The source of energy for the rotation of bacterial flagella; approximately $1000$ protons are translocated per rotation.

Gliding Motility

Movement of non-swimming bacteria across solid surfaces, requiring contact and sometimes involving polysaccharide slime or adhesion complexes.

Chemotaxis

Directed movement of a cell in response to a chemical gradient.

Phototaxis

Directed movement of a cell in response to light.

Aerotaxis

Movement of a cell toward or away from oxygen.

Osmotaxis

Movement of a cell toward or away from conditions of high ionic strength.

Hydrotaxis

Movement toward water, observed in some gliding cyanobacteria.