202 ^|

A Handbook of Biology

Hence, protons in the stroma decrease in number, while in the lumen, protons

are accumulated. This creates a proton gradient across the thylakoid

membrane and decrease in pH in the lumen.

(NEET 2016)



Breakdown of proton gradient leads to release of energy.



The gradient is broken down due to the movement of protons across the

membrane to the stroma through the transmembrane channel of the

F0 of the enzyme ATPase.

THË ÅTPåßë (ÅTP SÝÑTHÅSË)

Consists of two parts:



F0 : It is embedded in the membrane and forms a transmembrane channel

that carries out facilitated diffusion of protons across the membrane.



F1: It protrudes on the outer surface of the thylakoid membrane. The

energy due to breakdown of gradient causes a conformational change

in the F1 particle. It makes the enzyme to synthesise ATP molecules.

Thus,

chemiosmosis

requires a

membrane, a

proton pump, a

proton gradient and

ATPase.

ATPase has a

channel that allows

diffusion of protons

back across the

membrane. This

releases energy to

activate ATPase

enzyme that

catalyses formation

of ATP.

Energy is

used to pump

protons across

a membrane,

to create a

gradient or a high

concentration of

protons within the

thylakoid lumen.