A slice through a cell

Imagine cutting a human cell with an impossibly thin knife and looking at the cut face. Every coloured blob is a single molecule, about a thousand times smaller than the cell itself. The view is roughly a micrometre across.

Membranes

The tan bands are lipid bilayers, two layers of fatty molecules just 5 nm thick. Where the slice cuts one you can see the lipids side by side, tails pointing inward. They wrap the cell, its mitochondrion, the endoplasmic reticulum, the Golgi and the nucleus.

A crowd in constant motion

The space between is packed with proteins, jostling all the time. Nothing here is still: motors walk, filaments grow and shrink, ribosomes read messages and build new proteins.

Things to find

Kinesin walking a vesicle along a microtubule; a patch of membrane pulled inside in a cage of clathrin; ATP synthase spinning on the folds of the mitochondrion; cargo slipping through a nuclear pore; RNA polymerase reading DNA in the nucleus. Turn on labels, or click anything to name it.

Atoms

Zoom into the slice beside an ATP synthase, and you can sink ten times closer, to the atoms of the real human enzyme as cryo-electron microscopy resolved them. Protons flowing back into the matrix through its motor turn the rotor, a third of a turn at a time; each third, the head makes a molecule of ATP, the fuel nearly everything else in the cell runs on, and lets it go.

Deeper in

Keep zooming in. At one of the synthase’s catalytic sites, ADP and phosphate are pressed together with each turn of the rotor, and their new bond makes ATP. The phosphorus at the heart of that bond is drawn as quantum mechanics describes it: its electrons are not tiny planets but clouds of probability. At its centre, about thirty thousand times smaller, sits the nucleus, fifteen protons and sixteen neutrons; and inside each proton, three quarks, bound by a churning field of gluons.

The tour

The Tour button, or T, takes you through every level, from a whole person to a single proton: step on with its arrows at your own pace, or press play and it glides on by itself. Look around whenever you like; it waits for you.

The lobule

Out past the whole cell, its acinus is one of thousands, hung like grapes on a branching tree of ducts that carry their enzymes away toward the gut, each acinus wrapped in a basket of capillaries. Among them sits an islet of Langerhans, a cluster of the cells that make insulin and glucagon and release them into the blood.

The pancreas

Further out, the lobule is one of thousands packed side by side in the pancreas, a gland about 15 cm long lying behind the stomach. Each lobule’s duct leaves it and joins its neighbours’ in the thin walls between them, gathering into the main pancreatic duct, which runs the gland’s length and empties its enzymes into the duodenum. An artery and a vein run beside every duct.

The body

Further still, the pancreas lies among the organs of digestion: the liver, the stomach and spleen, the kidneys, the gut. The cut runs through all of them, showing what is inside. Out at the whole person, the skin turns to glass round the skeleton and the brain, and the pancreas glows gold where it lies.

The whole cell

Zoom out as far as the slice goes, and you can rise ten times higher: the slice becomes a window in the base of a whole cell. It is one of six pancreatic cells ringed around a tiny space, the lumen, where they release digestive enzymes bound for the gut. The rough ER wrapped around each nucleus makes the enzymes, the Golgi packs them into zymogen granules, and the granules gather by the lumen until they are let out. That happens in beats: a wave of calcium sweeps each cell from the lumen to its base, passing from cell to cell, and as it rises granules fuse with the membrane and empty into the lumen. All the while microtubules carry cargo toward the lumen, and messenger RNA leaves each nucleus through its pores. Around the acinus lies connective tissue, seen in depth below the cut: collagen and the fibroblasts that make it, capillaries where red blood cells pass in single file, and more acini, deeper.

An artistic simulation inspired by Evan Ingersoll and Gaël McGill’s cellular landscapes. Sizes of molecules are close to life; organelles are smaller than real ones so they fit, and every process runs far slower than in life so it can be seen. The whole cell, and everything out to the whole person, keeps the slice’s scale, a third of life size; seen from that far out, each dot stands for a cluster of molecules. Deeper in, sizes are true, but what is drawn is an illustration: electron clouds have no colour, and quarks cannot be seen.