Metabolism — Catabolism vs. Anabolism

Catabolism: Breaking down molecules to release energy (ATP). Examples: glycolysis, beta-oxidation, Krebs cycle.

Anabolism: Building up molecules using energy. Examples: gluconeogenesis, fatty acid synthesis, protein synthesis.

Carbohydrate metabolism:

High blood glucose → insulin → glucose uptake → glycolysis → glycogen synthesis

Low blood glucose → glucagon → glycogen breakdown (glycogenolysis) → gluconeogenesis

Lipid metabolism:

Beta-oxidation — fatty acids broken down in mitochondria → acetyl-CoA → Krebs cycle

Fatty acids yield far more ATP per carbon than glucose

Ketogenesis — excess acetyl-CoA → ketone bodies (during starvation or low carb)

Protein metabolism:

Amino acids deaminated → ammonia → urea cycle (liver) → urea excreted by kidneys

Carbon skeletons enter metabolic pathways as pyruvate, acetyl-CoA, or Krebs intermediates

Key regulatory hormones: Insulin (anabolic, stores energy), Glucagon (catabolic, releases energy), Cortisol (catabolic under stress)

Reference:

Wikipedia: Metabolism

https://en.wikipedia.org/wiki/Metabolism