CytoPac: Organelle Assembler

A nod to Jetpac (Ultimate Play the Game, 1983) on the ZX Spectrum. Instead of building a rocket and filling it with fuel, you build an organelle (nucleus, mitochondrion, Golgi apparatus, chloroplast) and feed it the right molecules, while free radicals, proteases and toxins try to stop you.

The science

• You are a kinesin. Kinesins are motor proteins that walk along microtubules, part of the cell’s cytoskeleton, using energy from ATP to carry cargo such as vesicles and organelles. The platforms in the game are microtubules.
• The organelles. The nucleus holds the cell’s DNA. The mitochondrion makes most of the cell’s ATP, starting from pyruvate, the end product of glycolysis. The Golgi apparatus modifies, sorts and packs proteins into vesicles. The chloroplast, found in plant cells, captures the energy of light (photons) in photosynthesis.
• Getting into the nucleus. Proteins made in the cytoplasm enter the nucleus through nuclear pores, carried by transport proteins called importins, which recognise a short tag on their cargo, the nuclear localisation signal. Some viruses hijack this: see the Hendra and Nipah virus W proteins with importin α, from Kate Smith’s PhD project, which I co-supervised.
• The enemies. Free radicals and reactive oxygen species damage DNA, proteins and lipids; proteases are enzymes that break proteins down.
• A new bot. Now and then a ribosome drifts by. Ribosomes read messenger RNA and build proteins from it (translation): touch it and it makes you a new kinesin.

Where the game cuts corners

• Real cells don’t build organelles from parts like a rocket kit. Mitochondria and chloroplasts grow and divide, much as the bacteria they descend from once did (the endosymbiotic theory).
• A kinesin doesn’t fly or jump. It walks along a microtubule on its two motor heads, one step of about 8 nanometres at a time, and most kinesins only walk one way (towards the microtubule’s “plus” end); dynein carries cargo the other way. Sadly, nobody has found a kinesin with a jetpack.