Glyceraldehyde is a simple three-carbon sugar and a key intermediate in carbohydrate metabolism — the crossroads where several pathways meet. Its phosphorylated form, glyceraldehyde-3-phosphate, sits at the heart of glycolysis: the energy-releasing breakdown of glucose, where each glucose molecule is split into two three-carbon units that cascade down to pyruvate. The same molecule runs in reverse during gluconeogenesis and feeds into the Calvin cycle of photosynthesis. Glyceraldehyde is also historically fundamental: the D- and L- forms of this smallest chiral sugar became the reference standard for describing the handedness of all other sugars — every “D-sugar” is named relative to D-glyceraldehyde.