Anabolism: The Biosynthetic Pathways That Build Molecules

Anabolism (from Greek anabole, "to build up") encompasses all metabolic pathways that synthesize complex molecules from simpler precursors, requiring energy input (endergonic).

Core Principles

• Energy coupling: Driven by ATP hydrolysis and reducing power (NADPH, NADH).
• Substrates: Amino acids → proteins; monosaccharides → polysaccharides; fatty acids + glycerol → triglycerides; nucleotides → nucleic acids.
• Key pathways: Gluconeogenesis, glycogenesis, lipogenesis, protein synthesis, nucleotide synthesis.

Anabolism vs. Catabolism

Feature	Anabolism	Catabolism
Direction	Build up	Break down
Energy	Consumes (endergonic)	Releases (exergonic)
Key molecules	ATP, NADPH	ATP, NADH, FADH2
Example	Protein synthesis	Glycolysis, β-oxidation

Regulation

• Hormonal: Insulin (anabolic), glucagon/cortisol (catabolic).
• Allosteric: ATP/AMP ratio, citrate, acetyl-CoA.
• Substrate availability.

Anabolic Steroids vs. Anticatabolic Agents

• Anabolic steroids (testosterone, trenbolone): Bind androgen receptor → increase protein synthesis, muscle/bone growth.
• Anticatabolic agents (clenbuterol, β2-agonists): Inhibit protein degradation pathways (ubiquitin-proteasome) without directly stimulating synthesis.

Physiological Importance

Anabolism enables growth, repair, energy storage, and reproduction. Dysregulation underlies metabolic diseases (diabetes, cachexia, cancer).