{"format":"molecular-machines.cards","version":1,"updated":"2026-10-12","decks":[{"machine":"kinesin","name":"Kinesin","count":10,"url":"/learn/cards/kinesin.json"}],"cards":[{"id":"kinesin-direction","machine":"kinesin","kind":"qa","prompt":"Kinesin is a motor that carries cargo along microtubule tracks. In a nerve cell it pulls cargo outward, away from the cell body. Toward which end of the microtubule does it walk?","answer":"Toward the plus end.","explanation":"Dynein runs on the same tracks and pulls cargo the other way.","section":"summary","topic":"purpose","sources":["machine:summary","machine:tagline","story:summary"],"tags":["direction","transport"],"difficulty":1,"url":"/machines/kinesin#summary","cites":[{"source":"machine:summary","machine":"kinesin","label":"Summary","section":"summary"},{"source":"machine:tagline","machine":"kinesin","label":"Summary","section":"summary"},{"source":"story:summary","machine":"kinesin","label":"Big picture","section":"story"}]},{"id":"kinesin-drift-time","machine":"kinesin","kind":"qa","prompt":"A nerve cell can run about a metre, from your spine to your foot, and its proteins are made near the spine. If those proteins only drifted, roughly how long would the trip take?","answer":"About 300 years.","explanation":"Kinesin motors carry the cargo instead, so fast transport makes the trip in a few days.","section":"story","topic":"numbers","sources":["fact:K2","fact:K3","stop:race"],"tags":["diffusion","axon","scale"],"difficulty":1,"url":"/machines/kinesin#story","cites":[{"source":"fact:K2","machine":"kinesin","label":"Time for a protein to drift 1 m by diffusion: 300 years","section":"story"},{"source":"fact:K3","machine":"kinesin","label":"Speed of fast outward transport in axons: 200–400 mm per day","section":"story"},{"source":"stop:race","machine":"kinesin","label":"Big picture: Drift or motor","section":"story"}]},{"id":"kinesin-atp-per-step","machine":"kinesin","kind":"qa","prompt":"Each kinesin step moves the cargo about 8 nm, the length of one building block of the microtubule track. What does each step cost the motor?","answer":"One ATP.","explanation":"The motor splits one ATP for each 8 nm step, so at low load it wastes almost none.","section":"summary","topic":"numbers","sources":["stat:ATP per step","machine:energy","stat:Step size"],"tags":["energy","step"],"difficulty":1,"url":"/machines/kinesin#summary","cites":[{"source":"stat:ATP per step","machine":"kinesin","label":"Key number: ATP per step","section":"summary"},{"source":"machine:energy","machine":"kinesin","label":"Summary","section":"summary"},{"source":"stat:Step size","machine":"kinesin","label":"Key number: Step size","section":"summary"}]},{"id":"kinesin-hand-over-hand","machine":"kinesin","kind":"qa","prompt":"Kinesin has two identical heads. Scientists put a dye on just one head and watched it walk. The dye jumped about 17 nm, then stayed still for a step, then jumped again. What does that show about how kinesin walks?","answer":"The heads take turns: the rear head swings past the bound head and lands ahead, hand over hand.","explanation":"Each head moves about twice as far as the cargo, which moves 8 nm per step.","section":"evidence","topic":"cycle","sources":["evidence:yildiz2004-head-step","mechanism:The rear head swings forward","stat:Head step"],"tags":["hand-over-hand","heads"],"difficulty":2,"url":"/machines/kinesin#evidence","cites":[{"source":"evidence:yildiz2004-head-step","machine":"kinesin","label":"Step of a single labelled kinesin head (Yildiz A 2004)","section":"evidence","anchor":"ev-yildiz2004-head-step"},{"source":"mechanism:The rear head swings forward","machine":"kinesin","label":"Step: The rear head swings forward","section":"mechanism"},{"source":"stat:Head step","machine":"kinesin","label":"Key number: Head step","section":"summary"}]},{"id":"kinesin-diffusion-search","machine":"kinesin","kind":"qa","prompt":"When ATP binds the front head, a short strand zips onto it and points forward, so the free head lands ahead. But this zipping is no leg muscle. What actually carries the free head to its next site?","answer":"Random jiggling by heat (diffusion).","explanation":"Diffusion does the travel and the zipped strand only sets the direction, like a small forward bias.","section":"mechanism","topic":"cycle","sources":["step:The free head searches","step:ATP binds and the neck linker zips","analogy:A walker with two feet"],"tags":["diffusion","power-stroke"],"difficulty":2,"url":"/machines/kinesin#mechanism","cites":[{"source":"step:The free head searches","machine":"kinesin","label":"Step: The free head searches","section":"mechanism"},{"source":"step:ATP binds and the neck linker zips","machine":"kinesin","label":"Step: ATP binds and the neck linker zips","section":"mechanism"},{"source":"analogy:A walker with two feet","machine":"kinesin","label":"Analogy: A walker with two feet","section":"story"}]},{"id":"kinesin-steps-per-run","machine":"kinesin","kind":"qa","prompt":"A single kinesin does not walk forever. After a while it lets go of the microtubule. About how many steps does it take before it falls off?","answer":"About 100 steps, a run of about 1 micrometre.","explanation":"One head always holds the track while the other moves, so the motor stays on for many steps.","section":"summary","topic":"numbers","sources":["stat:Run length","machine:summary","fact:s-run"],"tags":["processivity","run-length"],"difficulty":1,"url":"/machines/kinesin#summary","cites":[{"source":"stat:Run length","machine":"kinesin","label":"Key number: Run length","section":"summary"},{"source":"machine:summary","machine":"kinesin","label":"Summary","section":"summary"},{"source":"fact:s-run","machine":"kinesin","label":"Distance walked before letting go: 1 µm","section":"story"}]},{"id":"kinesin-teams-of-motors","machine":"kinesin","kind":"qa","prompt":"One kinesin lets go after about a micrometre, but a nerve cell can be a metre long. How does the cargo still reach the far end?","answer":"Teams of motors grab on again and again.","explanation":"A cargo bubble carries several motors, so when one lets go, others keep it on the track.","section":"story","topic":"purpose","sources":["analogy:A delivery truck on a highway","fact:K8","fact:K6"],"tags":["teams","axon"],"difficulty":1,"url":"/machines/kinesin#story","cites":[{"source":"analogy:A delivery truck on a highway","machine":"kinesin","label":"Analogy: A delivery truck on a highway","section":"story"},{"source":"fact:K8","machine":"kinesin","label":"Steps for one kinesin to cross 1 m: 1.25 × 10^8 steps, one ATP each","section":"story"},{"source":"fact:K6","machine":"kinesin","label":"Kinesins on one brain vesicle: 1–4 kinesins","section":"story"}]},{"id":"kinesin-dynein-tug","machine":"kinesin","kind":"qa","prompt":"Cargo bubbles in a nerve cell carry more than one kind of motor. Kinesin pulls them outward. Which motor on the same tracks pulls the other way, back toward the cell body?","answer":"Dynein.","explanation":"Vesicles from the brain carry a few kinesins and a few dyneins at once.","section":"story","topic":"purpose","sources":["link:dynein","fact:K6","stop:vesicle"],"tags":["dynein","link"],"difficulty":1,"url":"/machines/kinesin#story","cites":[{"source":"link:dynein","machine":"kinesin","label":"Link to Dynein","section":"story"},{"source":"fact:K6","machine":"kinesin","label":"Kinesins on one brain vesicle: 1–4 kinesins","section":"story"},{"source":"stop:vesicle","machine":"kinesin","label":"Big picture: Vesicle team","section":"story"}]},{"id":"kinesin-nerve-disease","machine":"kinesin","kind":"qa","prompt":"Long nerve cells depend on kinesin to keep their far ends supplied. What kind of illness can a mutation in a nerve kinesin gene cause?","answer":"Nerve disease, such as a hereditary spastic paraplegia or ALS.","explanation":"A mutation in the motor part of the nerve kinesin KIF5A causes one form of hereditary spastic paraplegia, and the same gene is linked to ALS.","section":"story","topic":"purpose","sources":["fact:K11"],"tags":["disease","nerve"],"difficulty":2,"url":"/machines/kinesin#story","cites":[{"source":"fact:K11","machine":"kinesin","label":"Kinesin gene linked to nerve disease: KIF5A gene","section":"story"}]},{"id":"kinesin-myosin-shared-core","machine":"kinesin","kind":"qa","prompt":"Kinesin walks on microtubules and myosin walks on actin, and their protein sequences are almost unrelated. What do their motor cores still share?","answer":"The same fold, so they probably share a common ancestor.","explanation":"A switch in the core changes shape between the ADP and ATP states, much like in myosin and in G proteins.","section":"summary","topic":"debate","sources":["evolution:Common core with myosin","link:myosin","evolution:Switches shared with G proteins"],"tags":["evolution","myosin","link"],"difficulty":2,"url":"/machines/kinesin#summary","cites":[{"source":"evolution:Common core with myosin","machine":"kinesin","label":"Common core with myosin","section":"summary"},{"source":"link:myosin","machine":"kinesin","label":"Link to Myosin","section":"story"},{"source":"evolution:Switches shared with G proteins","machine":"kinesin","label":"Switches shared with G proteins","section":"summary"}]}]}