Flip the membrane and the H+ and ATP sides flip too
- The idea
- Predict
- See it
- Why
- Check
The idea
“H+ and ATP end up on the same sides as in a normal cell, whatever the setup.”
You learned one picture, with H+ in the lumen and ATP in the stroma. An experiment can turn the membrane around.
The short version
The mistake: H+ and ATP end up on the same sides as in a normal cell, whatever the setup.
What's actually true: Each protein works from its own membrane faces, so flipping the membrane flips where H+ and ATP end up.
- The electron transport chain pumps H+ from the matrix side to the other side. In a chloroplast, it pumps from the stroma into the lumen.
- ATP synthase lets H+ flow back. Its head, the part that makes ATP, sits on the matrix or stroma side, so ATP forms there.
On the exam: Check which way the membrane faces. H+ go where the chain pumps them, and ATP forms where the heads point.