In the catalytic mechanism of ATP synthase ( complex) in chloroplasts, where is the catalytic headpiece located?
Answer and explanation
Correct answer: A. Protruding into the stroma on the stromal surface of the thylakoid membrane
- Step 1: Chloroplast ATP synthase consists of two functional parts: and .
- Step 2: is a transmembrane channel that spans the thylakoid lipid bilayer, conducting protons down their electrochemical gradient from the lumen to the stroma.
- Step 3: is the peripheral catalytic headpiece that protrudes into the stroma, where it binds ADP and inorganic phosphate () to synthesize ATP.
Answer
Protruding into the stroma on the stromal surface of the thylakoid membrane
Why not the others: 'Embedded entirely within the hydrophobic core...' describes the proton channel, not ; 'Projecting into the thylakoid lumen...' reverses the topological orientation; ATP is required in the stroma for the Calvin cycle; 'Attached to the outer membrane...' confuses the thylakoid membrane with the outer chloroplast envelope.
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