Bacterial Cell Wall Architecture and Photophosphorylation Pathways

Comprehensive vocabulary flashcards detailing the anatomical components of Gram-positive and Gram-negative bacterial cell envelopes alongside the molecular machinery and pathways of cyclic and noncyclic photophosphorylation.

Bacterial cell wall architectures (Gram-positive vs. Gram-negative)

The structural distinction between bacterial envelopes: Gram-positive envelopes consist of a thick peptidoglycan layer with teichoic and lipoteichoic acids overlying a cytoplasmic membrane; Gram-negative envelopes consist of an outer membrane with lipopolysaccharide (LPS containing lipid A) and porins, a periplasmic space enclosing a thin peptidoglycan layer, and an inner cytoplasmic membrane.

Gram-positive cell wall

A bacterial cell wall type characterized by a thick peptidoglycan layer located external to the cytoplasmic membrane and embedded with teichoic acid and lipoteichoic acid.

Gram-negative cell wall

A bacterial cell wall type characterized by an outer membrane containing lipopolysaccharide (LPS) with lipid A, porin channels, a periplasmic space containing a thin peptidoglycan layer, and an inner cytoplasmic membrane.

Peptidoglycan layer

The rigid structural layer of the bacterial cell wall situated outside the cytoplasmic membrane, presenting as a thick outer coat in Gram-positive cells and as a thin layer within the periplasmic space in Gram-negative cells.

Teichoic acid

An acidic polymer embedded within the peptidoglycan layer of Gram-positive bacterial cell walls.

Lipoteichoic acid

A teichoic acid polymer in Gram-positive bacteria that spans the entire peptidoglycan layer and anchors directly into the underlying cytoplasmic membrane.

Outer membrane of cell wall

A specialized lipid bilayer located exterior to the peptidoglycan layer in Gram-negative bacteria, containing phospholipids, porin channels, and an outer lipopolysaccharide (LPS) layer.

Periplasmic space

The fluid-filled compartment situated between the outer membrane and the cytoplasmic membrane in Gram-negative bacteria that contains the peptidoglycan layer.

Porin

A protein channel traversing the outer membrane of Gram-negative bacteria that permits the passive transport of molecules across the membrane.

Lipopolysaccharide (LPS) layer

The outer leaflet structure of the Gram-negative outer membrane containing lipid A.

Lipid A

The lipid component that anchors the lipopolysaccharide (LPS) layer into the outer membrane of Gram-negative bacteria.

Integral protein

A membrane protein permanently attached to and embedded within the phospholipid layers of the cytoplasmic or outer bacterial membranes.

Photophosphorylation mechanisms (cyclic vs. noncyclic)

The two light-dependent processes of ATP production: cyclic photophosphorylation circulates electrons exclusively through Photosystem I to pump $H^+$ and generate $ATP$, while noncyclic photophosphorylation utilizes both Photosystem II and Photosystem I, splits $H_2O$ to generate $O_2$, and produces both $ATP$ and $NADPH$ for the Calvin-Benson cycle.

Cyclic photophosphorylation

A light-driven pathway where electrons excited at the reaction center of Photosystem I pass through an electron transport chain involving iron (Fe), cytochromes, and copper (Cu) and return to Photosystem I, establishing an $H^+$ gradient that powers $ATP$ synthesis via ATP synthase.

Noncyclic photophosphorylation

A photosynthetic pathway in which light excites electrons in Photosystem II, water ($H_2O$) is photolyzed into protons ($H^+$) and oxygen ($O_2$), and electrons flow through quinone, cytochromes, copper (Cu), Photosystem I, iron (Fe), and NADPase to reduce $NADP^+$ into $NADPH$, while driving $ATP$ synthesis via ATP synthase.

Photosystem I

A pigment-protein complex with a reaction center that absorbs light energy to excite electrons in both cyclic and noncyclic photophosphorylation pathways.

Photosystem II

A photosystem complex in noncyclic photophosphorylation where absorbed light drives the excitation of electrons and the oxidation of water ($H_2O$) into oxygen ($O_2$) and protons ($H^+$).

Reaction center

The specific region within Photosystem I and Photosystem II where light energy is harvested to excite electrons ($e^-$) and initiate the electron transport chain.

ATP synthase

A membrane-bound rotary enzyme complex that harnesses the potential energy of a translocated proton ($H^+$) gradient across the cytoplasmic or thylakoid membrane to phosphorylate $ADP + P$ into $ATP$.

NADPase

An enzyme in noncyclic photophosphorylation that receives electrons from iron (Fe) and transfers them along with protons ($H^+$) to $NADP^+$ to form $NADPH$.

Quinone

An electron carrier in noncyclic photophosphorylation that shuttles excited electrons from the reaction center of Photosystem II to cytochromes.

Calvin-Benson cycle

The biochemical cycle located in the cytoplasm of prokaryotes or stroma of chloroplasts that utilizes the $ATP$ and $NADPH$ produced by noncyclic photophosphorylation.