Each ring is one monosaccharide (a pyranose sugar unit). Rings join end-to-end through a glycosidic bond: the anomeric carbon (C1) of one ring loses a water molecule with a hydroxyl of the next ring's C4 (or C6 for a branch), forming a C–O–C bridge. Whether that bridge sits α (below the ring plane) or β (above it) at the anomeric carbon decides the whole polymer's shape:
- Starch (amylose) — all α(1→4) bonds. Every linkage bends the chain the same way, so it curls into a tight left-handed helix (this is exactly why iodine turns starch solutions blue-black: I₂ molecules slot inside the helix's hollow core).
- Cellulose — all β(1→4) bonds. Each successive ring is flipped 180° relative to its neighbour, so the bends cancel out and the chain runs straight, letting many chains pack side-by-side into rigid, H-bonded fibrils (plant cell walls, cotton fibre).
- Chitin — the same straight β(1→4) backbone as cellulose, but each ring carries an N-acetyl group (dark bead) instead of a plain hydroxyl — the polymer of insect exoskeletons and fungal cell walls.
- Glycogen / amylopectin — an α(1→4) helical backbone like starch, but roughly every 8–12 units an extra α(1→6) bond branches off a whole new side-chain, producing the bushy, highly branched storage granule shape that allows very fast enzymatic release of glucose.
Toggle mutarotation to see the anomeric carbon itself in motion: in solution, free (non-linked) reducing ends of a chain constantly interconvert between the α and β ring forms through an open-chain aldehyde intermediate, settling at a characteristic equilibrium mixture — this is why a freshly dissolved sugar's optical rotation drifts over time.
helix pitch ∝ twist angle per α(1→4) bond
straight run ∝ alternating 180° flip per β(1→4) bond
branch density ∝ 1 / branch interval