Foundations

Metabolism comprises the regulated chemical reactions of living systems.

Oxygenic photosynthesis couples light-energy capture to carbon fixation and releases oxygen from water.

Aerobic respiration couples nutrient oxidation to ATP production, using oxygen as the final electron acceptor.

Ecology examines organisms' interactions with one another and their physical environment.

Feedback can maintain internal variables within functional ranges.

Carbohydrates, lipids, proteins and nucleic acids organize much of cell chemistry.

Sequence, folding and assembly provide different levels of protein description.

A simple enzyme–substrate mechanism predicts saturating initial rates.

Coupled reaction pathways connect favourable chemistry with cellular work.

The canonical glycolytic pathway converts one six-carbon glucose into two three-carbon pyruvates.

Pyruvate dehydrogenase converts pyruvate to acetyl-CoA with CO₂ release and NADH formation.

A respiratory electron-transport chain couples favourable electron transfers to an electrochemical proton gradient across a membrane.

Fermentation regenerates oxidized electron carriers by transferring electrons to metabolic organic intermediates, permitting substrate-level ATP production without the aerobic respiratory chain.

In oxygenic photosynthesis, photosystems II and I use absorbed light to drive electron transfer from water toward reduction of NADP⁺.

The Calvin–Benson cycle carboxylates ribulose-1,5-bisphosphate through RuBisCO, reduces the resulting carbon compounds using ATP and NADPH, and regenerates the acceptor.

NAD(H) and NADP(H) commonly carry hydride equivalents, while flavins can participate in one- or two-electron chemistry.

For a typical saturated even-chain fatty acyl-CoA, β-oxidation repeats oxidation, hydration, oxidation and thiolytic cleavage.

In the canonical fatty-acid-synthase pathway, ATP-dependent acetyl-CoA carboxylation supplies malonyl units.

Gluconeogenesis makes glucose from suitable noncarbohydrate precursors.

Glycogen synthase uses activated UDP-glucose to extend glucan chains, while branching creates additional nonreducing ends.

The oxidative pentose-phosphate route converts glucose-6-phosphate toward pentose phosphate with CO₂ release and NADPH formation.

PLP-dependent transamination transfers an amino group between an amino acid and a keto acid without requiring free ammonia as the immediate product.

The mammalian urea cycle combines nitrogen from ammonia and aspartate with bicarbonate-derived carbon to form urea.

De novo purine synthesis builds a ring on activated ribose toward IMP, then branches toward AMP and GMP.

In the stated reversible single-substrate Michaelis–Menten model, competitive inhibition increases apparent Km while leaving Vmax unchanged.

Metabolic flux responds to substrate/product availability, allosteric effectors, covalent enzyme modification and cellular demand.

Rubisco's oxygenase activity produces a three-carbon phosphoglycerate and a two-carbon phosphoglycolate from RuBP.

In a common C4 route, PEP carboxylation supplies four-carbon acids that deliver CO₂ to Rubisco in a spatially separated compartment.

Chloroplast triose-phosphate exchange with inorganic phosphate connects photosynthetic fixation to cytosolic sucrose synthesis.

Reaction stoichiometry relates species-amount changes to reaction and exchange fluxes.