Biochemistry: Photosynthesis and Oxidative Phosphorylation

Vocabulary practice flashcards covering photophosphorylation, photosystems, the Calvin cycle, the mitochondrial electron transport chain, and ATP synthase regulation from Midterm Exam 3.

Cytochrome b6f

A transmembrane complex in the photosynthetic electron transport system that operates alongside photosystem I (PSI) and photosystem II (PSII).

Photosystem II (PSII)

A photosynthetic complex in plants and cyanobacteria that oxidizes $H_2O$ to supply electrons into the photosynthetic electron transport chain.

Photosystem I (PSI)

A photosynthetic complex in plants and cyanobacteria that uses light energy to reduce $NADP^+$ to NADPH.

Pheophytin

An early electron carrier in photosystem II; blocking electron transfer through it stops PSII electron flow and slows PSI electron flow by restricting it to cyclic transfer.

Plastoquinones

Lipid-soluble electron carriers in Z-scheme photosynthesis that transfer electrons through participation in a Q cycle.

Photophosphorylation

Light-driven ATP synthesis that, like oxidative phosphorylation, fundamentally requires the formation of a transmembrane proton gradient.

Transketolase

A Calvin cycle enzyme that catalyzes the reaction of fructose 6-phosphate and glyceraldehyde 3-phosphate to yield xylulose 5-phosphate and erythrose 4-phosphate.

Rubisco Light-Activation Mechanisms

The illumination-dependent activation of Calvin cycle enzymes driven by increased stromal pH, light-driven stromal influx of $Mg^{2+}$, and disulfide bond reduction by thioredoxin.

Cyclic Photophosphorylation

A photosynthetic electron pathway favored at high NADPH/$NADP^+$ ratios where $O_2$ production decreases, NADPH production ceases, and ATP is generated.

$P_i$-Triose Phosphate Antiporter

A chloroplastic transport protein that exports Calvin-cycle-derived dihydroxyacetone phosphate into the cytosol in exchange for inorganic phosphate ($P_i$).

Thioredoxin

A regulatory protein reduced by electrons from ferredoxin during illumination that activates key Calvin cycle enzymes by reducing their critical disulfide bonds.

Complex II (Succinate Dehydrogenase)

A mitochondrial electron transport complex whose inhibition reduces overall electron flux without altering the free energy generated by electrons entering from NADH.

$\gamma$ Subunit of ATP Synthase

The central rotating shaft of $F_0F_1$ ATP synthase whose rotation drives conformational transitions within the stationary catalytic $\alpha\beta$ dimers.

Mitochondrial Phosphate Carrier

A transport system that imports inorganic phosphate ($P_i$) from the cytosol into the mitochondrial matrix driven by the simultaneous symport of $H^+$.

Antimycin A

A potent respiratory inhibitor that blocks ubiquinol oxidation, demonstrating higher toxicity than rotenone because it halts electron transfer originating from both Complex I and Complex II.

Rotenone

A specific inhibitor of NADH dehydrogenase (Complex I) in insect and fish mitochondria that halts electron transfer from NADH to ubiquinone.

2,4-Dinitrophenol (DNP)

A chemical uncoupler that dissipates the mitochondrial proton gradient, causing continuous fuel oxidation and heat release without ATP synthesis.

Respiratory Control

The regulatory dependence of the mitochondrial electron transport rate and fuel oxidation on the availability of ADP and an active ATP synthase.

$F_0$ Subunit

The membrane-embedded sector of the $F_0F_1$ ATP synthase complex consisting of a ring of proton-carrying polypeptides.