The spinning engine of ATP

Science · Biochemistry & Molecular Biology · ages 20-22

Name ______________________ Date ____________

Which step of the catalytic cycle costs energy?
- Releasing the finished ATP from its site
- Forming the bond between the raw materials
- Binding the raw materials to the site
How is proton flow linked to ATP formation?
- Protons smash ATP apart to release energy
- Protons bypass the enzyme and make ATP alone
- Protons turn the rotor, cycling each site through binding, forming, and release
ATP is abundant and cellular work is low. What happens to electron flow?
- It speeds up to store even more ATP
- It slows, since the built gradient has no outlet
- It reverses direction permanently
The gradient collapses entirely. What does the enzyme do?
- It waits patiently for protons to return alone
- It hydrolyzes ATP to pump protons and rebuild the gradient
- It dissolves into separate pieces permanently
Hard work consumes ATP and ADP rises. What does the synthase do?
- It stops entirely until ATP recovers alone
- It turns faster, draining the gradient and pulling more electron flow
- It runs in reverse and destroys the gradient
What does the rotor turn against?
- The stationary catalytic head, whose sites change shape as it passes
- The outer cell wall, which spins with it
- Free floating ATP molecules in the cytosol
Each full turn of the rotor produces exactly one ATP.
Circle one: True False
A drug locks the rotor. Protons keep pumping briefly, then everything stalls. Why the stall?
- The gradient builds with no outlet and resists further pumping
- Electrons vanish from the mitochondrion entirely
- ATP attacks and destroys the whole chain

Answer key

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The spinning engine of ATP W1-mt_PDe3f-FVfD-s1

Releasing the finished ATP from its site · The bond forms readily once substrates are held. Prying the finished product loose is the costly move.
Protons turn the rotor, cycling each site through binding, forming, and release · Flow becomes rotation, and rotation becomes chemistry. Each site takes its turn as the rotor passes.
It slows, since the built gradient has no outlet · A full gradient with nowhere to go resists further pumping. Supply idles when demand sleeps.
It hydrolyzes ATP to pump protons and rebuild the gradient · Reverse running spends ATP to restore the gradient. The machine works both ways when forced.
It turns faster, draining the gradient and pulling more electron flow · Rising ADP opens the outlet. Faster turning drains the gradient, which invites more pumping.
The stationary catalytic head, whose sites change shape as it passes · Motion against a fixed frame is what squeezes the sites through their states. Two spinning parts would achieve nothing.
False · Three sites take turns each revolution, so one turn makes three ATP. One would waste two sites.
The gradient builds with no outlet and resists further pumping · Apply the no outlet rule: a locked rotor is a closed drain. Buildup pushes back until pumps stop.