Metabolic organization: anabolism/catabolism, energy currencies, coupled reactions, regulation.
Metabolism Overview
Metabolism
The sum of enzyme-catalysed reactions in a cell — catabolism (breakdown releasing energy) plus anabolism (biosynthesis consuming energy).…
Anabolism
Endergonic biosynthetic arm of metabolism: building macromolecules from precursors, powered by ATP hydrolysis and NADPH reducing…
Catabolism
Exergonic degradative arm of metabolism: breakdown of macromolecules releasing energy captured as ATP and NADH.
ATP/ADP cycle
Principal energy currency of the cell: ATP hydrolysis (ΔG°' ≈ −30.5 kJ/mol) drives endergonic reactions; ADP is rephosphorylated by…
NAD+/NADH cycle
Primary electron carrier of catabolism (ΔE°' = −0.32 V). NAD+ is reduced to NADH during substrate oxidation; NADH is reoxidised at ETC…
Reducing equivalent
Currency of biological reduction reactions: NADH and NADPH carry hydride (H−) to reduction steps; NADH drives catabolism, NADPH drives…
Substrate-level phosphorylation
Direct transfer of a phosphate group from a high-energy metabolic intermediate to ADP. Examples: phosphoglycerate kinase, pyruvate kinase,…
Metabolic flux
Rate of material flow through a metabolic pathway (mol·s⁻¹). Measured by 13C-MFA + FBA; set by enzyme levels, cofactor availability,…
Metabolic control analysis
Kacser-Burns / Heinrich-Rapoport 1973-74 theory: flux control is distributed across enzymes, quantified by flux-control coefficients C^J_i…
Feedback inhibition
Pathway end-product allosterically inhibits the committed enzyme (first irreversible step), preventing overproduction. Classic: CTP…