PoreSort
A channel in a cell membrane is not a wall with a doorman. It is a shaped hole: things pass when they fit, and they move down whatever gradient already exists — nothing is pulled or pumped through. For each real channel below, predict which particles pass and which are blocked, then see the real AlphaFold structure. Everything runs locally; nothing about you is collected.
This is the tool — a free prediction game. You commit your guess before the answer shows, so the score is prediction, not luck. Each game draws as many blocked particles as passing ones, so saying “Blocked” every time cannot win. The three channels, their particles, and the reasons are listed in full in the guide below, which works with or without JavaScript. A native version, when it ships, adds offline use and reading tiers; it never gates the web.
Loading the game… If it does not start, the full channel guide below still works.
How to play. Press Start. For each particle, predict Passes or Blocked — tap a bin, click a button, or press 1/P for Passes, 2/B for Blocked. The answer and the reason appear; press Enter or Next to continue. There is no timer and no way to lose.
Why the pore you just sorted matters
Aquaporin-1 lets water through but not the protons (H⁺) that ride on water. Its narrowest point, the ar/R constriction (aromatic and arginine side chains), is the size filter; the two NPA motifs that meet at the centre of the channel block protons from hopping along the single-file water chain. Peter Agre shared the 2003 Nobel Prize in Chemistry for discovering aquaporins. Your kidneys reclaim most of the roughly 180 litres of fluid they filter each day, much of it through aquaporin channels.
The channels
Aquaporin-1 AQP1 · P29972
A water channel in red blood cells and the kidney. Its pore has a very narrow neck, so only small, uncharged particles that fit the neck slip through — down whatever gradient already exists.
Answer key — open it after you play
| Particle | Passes? | Why |
|---|---|---|
| Water | Passes | Small and uncharged — slips single-file through the narrow neck. |
| Protons (H⁺) | Blocked | The pore breaks the water chain a proton would need, so protons do not pass even though water does. |
| Sodium (Na⁺) | Blocked | Not an ion channel — a charged ion does not fit the uncharged neck. |
| Glucose | Blocked | Far too large for the narrow neck. |
| Urea | Blocked | A strict water pore; urea passes through a different family member (an aquaglyceroporin). |
GLUT4 SLC2A4 · P14672
A glucose carrier in muscle and fat. It does not pump: it lets glucose cross by opening to one side, then the other, so glucose moves down its concentration gradient (facilitated diffusion).
Answer key — open it after you play
| Particle | Passes? | Why |
|---|---|---|
| Glucose | Passes | The pocket fits glucose; it crosses down its gradient as the carrier flips — no pumping. |
| Sodium (Na⁺) | Blocked | GLUT4 carries no ions (unlike a sodium-coupled sugar transporter). |
| Water | A little (both count) | A little passes (Fischbarg et al. 1990), far less than through water channels such as aquaporins: both calls count. |
| 2-Deoxyglucose | Passes | A glucose look-alike with one oxygen missing; it fits the same pocket, which is why labs use it to measure GLUT4 uptake. |
| Fructose | Blocked | Shaped for glucose; fructose is carried by a different family member (GLUT5). |
| ATP | Blocked | Large and highly charged — does not fit and is not carried. |
CFTR CFTR · P13569
A chloride channel at cell surfaces (the one broken in cystic fibrosis). ATP binding opens the gate and ATP breakdown closes it again, but the ions themselves just flow down their gradient through the open pore — nothing is pumped.
Answer key — open it after you play
| Particle | Passes? | Why |
|---|---|---|
| Chloride (Cl⁻) | Passes | An anion channel; when ATP has opened the gate, chloride flows through down its gradient. |
| Bicarbonate (HCO₃⁻) | Passes | Another small anion that fits the open pore. |
| Thiocyanate (SCN⁻) | Passes | Another small negative ion that fits the open pore. |
| Sodium (Na⁺) | Blocked | The pore selects for negative ions, so a positive sodium ion does not pass. |
| Potassium (K⁺) | Blocked | A positive ion, excluded by the anion-selective pore. |
| Glucose | Blocked | Uncharged and too large for the anion pore. |
Methods & about
This is a teaching game, honest about being a simplification. Real channels are subtle: selectivity is a matter of degree, gating and permeation are separate steps, and a few channels conduct more than one thing. The game uses the clear, textbook cases. The point it operates is a common misreading: a channel is not a wall with a gatekeeper that decides or pulls — it is a shaped pore, and particles pass only when they fit, down their own gradient. The structures are real AlphaFold predictions fetched live from the AlphaFold database; the channel facts are authored and checked. The game keeps no score history, uses no accounts, and sends nothing anywhere.
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