Moleculoids

The game defines eight families of monster, each with its own speed, hit points and style of attack: Enzyme, Receptor, Transporter, Structural, Chaperone, Toxin, Nuclease and Antibody. Receptors keep their distance and shoot; Structural monsters, the heaviest, cannot be knocked back. A table assigns a different mix of families to each of the first five levels, but the function that builds the waves reads the table with the level fixed at 1, beside the comment "level 1 for now". Every wave of every level is therefore drawn from the first level's mix: Enzymes, Transporters, Receptors and Chaperones, with a Structural monster as the boss. Toxins, Nucleases and Antibodies never appear.^[2]

Each monster is a sprite rendered from a real structure, which turns through 32 frames.^[a] The game loads sprites from a list of 26 entries in three sizes, of which 17 have image files on the server.^[3] The small ones include two mutants of the lysozyme of the bacteriophage T4 and three sperm whale myoglobins carrying isocyanide ligands. Three of the eight small sprites are not proteins: 100D is a short chimeric RNA and DNA duplex bound to spermine, 105D a four-stranded DNA structure called an i-motif, and 107D a DNA duplex bonded to the antitumor antibiotic duocarmycin A.^[4] Enzymes, the commonest monsters, take their sprites from this group, so the game's most frequent enemy is drawn, three times in eight, as a piece of nucleic acid. The medium sprites include a paused RNA polymerase of the bacterium Escherichia coli, the kinase domain of Fyn bound to the drug saracatinib, the signaling protein H-Ras and three cryo-electron microscopy structures of the NMDA receptor, a glutamate receptor of the brain.

Of the five large entries, one has an image file: 11YE, "Curved structure of mPiezo1 in plasma membrane vesicles", a structure of the mouse Piezo1 channel with 29,295 atoms and a mass of 882 kilodaltons.^[3] Since the boss is always a Structural monster, and Structural monsters always use the large sprites, the boss of every level is the same molecule. Piezo1 is an ion channel that opens when the membrane around it is stretched, and it lets cells sense pressure and the shear of flowing blood. Its discovery was part of the work for which Ardem Patapoutian shared the 2021 Nobel Prize in Physiology or Medicine.^[5]

The pickups are molecules, fifteen in all, each with a game effect and a one-line gloss. Glucose restores 25 hit points; Caffeine adds 80 percent to speed for five seconds; Dopamine is worth 100 points, "reward!". Every boss drops the one legendary item, the Legendary Enzyme, labeled "+8 base melee damage" and "permanent!"^[2]

Several items behave differently from their descriptions. The Legendary Enzyme is applied twice, once by the item code and once by the game loop, and adds 16 points of melee damage. ATP promises "+50% speed & damage" and gives 50 percent more speed and 30 percent more damage. Glutathione, described as "Cleanse debuffs +15 HP", empties the player's list of active effects; the game has no debuffs, so what it removes are the player's own boosts. Coenzyme A, "Piercing projectiles", displays a badge and changes nothing. Six items never appear at all, because no monster that appears can drop them: Heme, Cholesterol, Morphine ("Invincibility" and "pain relief"), the homing Antibody, CRISPR, labeled "Instant kill 3 nearest enemies", and Plasmid, "Summon allied monster".^[2] The effects of the last two are left to the game loop by a comment in the item code, "CRISPR and summon handled in main.js", and the game loop does not handle them.

The game's first form was the one the menu still describes, modeled on Atari's 1979 arcade game Asteroids. Its files remain in a backup folder: the player flew a ship with three lives, protein structures drifted across a starfield, and a shot split a large protein into two medium fragments and a medium one into three small ones, each named after its parent with the suffix "(fragment 1)", "(fragment 2)" and so on. A flying saucer appeared every 18 to 30 seconds and fired every 1.5 seconds. Two known binding partners, if they touched, merged into a "super" complex worth 150 points.^[2]

In place of the hyperspace button of Asteroids, this version had a warp, usable once per level and guarded by a question. Pressing Q or E paused the game and asked, about one of the proteins on screen, "Which protein has a molecular weight of approximately" so many kilodaltons, or which had a given PDB identifier. The player had ten seconds to choose among the names of the proteins present. A right answer moved the ship to a random point near the center of the screen; a wrong answer, or none, cost a life.^[2]

The server still assembles levels in that format. For level n it picks min(3 + n, 8) large proteins, about half as many medium ones and as many small ones as large, at least three, and on even levels from 2 and on every third level it adds one of its pairs of binding partners, with an approximate dissociation constant and a line of biological context.^[2] It holds two pairs. One joins two structures of human hemoglobin, entries 4HHB and 1BBB, under the code comment "Hemoglobin chains (alpha/beta)". The other, commented "Heterodimer example", joins entry 1HX1, a fragment of the chaperone Hsc70 bound to a BAG domain, with entry 1HX2, a trypsin inhibitor from the fire-bellied toad Bombina bombina. Both pairs are described as a "Known biological complex" with a dissociation constant in the "~nM range (high affinity)".^[6]

The proteins were fetched in May 2026 by a script that searches the RCSB Protein Data Bank for entries in three bands of molecular weight, under 100 kilodaltons, 100 to 500 and over 500, downloads their coordinates, and renders each as a turntable of frames.^[6] Sixty structures were rendered, among them human hemoglobin. A review page, Gallerioid, titled "Moleculoids Sprite Review", lays them out with buttons marked Good and Bad and opens its review log with "No reviews yet".

The game entered the company's code repository on June 8, 2026, as part of a large commit whose message reads "Change 1: Implement logarithmic Y-axis range slider (±10 fA to ±600 nA)".^[7] The Asteroids version reported scores to a leaderboard and paid members 10 experience points for each level completed. The dungeon version sends nothing to the server. In July 2026 the same pipeline supplied the proteins of the Cell world in Universe Window, where visitors fly among protein models drawn at a scale of one ångström to ten centimeters.^[6]

The MoleculArcade menu lists five more games as "Coming Soon", each a molecular version of an arcade title: Pac-Protein, in which "a hungry enzyme" navigates "a maze of substrates"; Molecular Invaders, defending the cell membrane from "descending viral particles"; Centipeptide, in which shooting a polypeptide's bonds frees fragments that "become independent enzymes"; Ribo-Runner, a race along messenger RNA; and Crispr Command, in which the player guides a Cas9 complex to "Match the PAM site, cut the target, and defend the genome!"^[1]