Metabolism, Bioenergetics, and Systems Physiology
Thermodynamics of living systems
Energy coupling and flux
Cells are open systems that maintain order by coupling exergonic and endergonic reactions. Metabolic control is best studied through fluxes rather than metabolite abundances alone, because flux reflects network activity and constraint.
Quantitative lens
A metabolite can be highly abundant yet carry low flux, and vice versa. Flux and concentration are related but not identical observables.
Central pathways and control
Pathway coordination
Glycolysis, the TCA cycle, oxidative phosphorylation, fatty acid oxidation, and biosynthesis form an interconnected network governed by allosteric regulation, compartmentation, and hormonal control. System-level behavior often emerges from enzyme saturation, feedback inhibition, and substrate availability.
Which process directly uses a proton gradient to synthesize ATP?
Oxidative phosphorylation uses the electrochemical proton gradient across the inner mitochondrial membrane.
Correct answer: Oxidative phosphorylation
What is flux in metabolic systems biology?
Flux quantifies pathway throughput, usually in molecules per unit time or concentration per unit time.
Correct answer: The rate of flow through a metabolic pathway
Physiological integration
Levels of metabolic regulation
Allosteric regulation
- Fast control of enzyme activity
- Responds to immediate metabolite levels
Transcriptional regulation
- Slower but longer-lasting control
- Changes enzyme abundance
Why is metabolic flux analysis useful in systems biology?
Flux analysis reveals how control is distributed across pathways and how cells adapt to perturbations.
Correct answer: It helps infer pathway usage and control under perturbation
Name one major open question in metabolism research.
Disease, senescence, and developmental transitions involve complex and incompletely understood metabolic reprogramming.
Correct answer: How metabolic states are rewired in disease and aging