Question

Coupling factor-F occurs over
(a) Ribosome
(b) Stroma
(c) Matrix
(d) Thylakoids

Answer 1

ATPase complex is also known as the Coupling factor. F-ATPase is present in chloroplasts, mitochondria, and the plasma membrane of bacteria. They are present on the membrane-bound compartments inside chloroplasts. They are present on the site of the light-dependent reactions of photosynthesis. It performs the photosynthetic light-dependent reactions. membrane and light-independent reactions in the soluble stroma.

Complete answer:
Transmembrane ATPases are membrane-bound enzyme complexes/ion transporters that use ATP hydrolysis to drive the transport of protons across a membrane. The ATPase enzyme consists of two parts: ${ F }_{ 0 }$ and ${ F }_{ 1 }$. The former is embedded in the membrane and forms a transmembrane channel in the thylakoid that carries out facilitated diffusion of protons across the membrane. The latter is protruding on the outer surface of the thylakoid membrane on the side that faces the stroma. The thylakoid membrane itself is not permeable to protons. The protons, therefore, flow towards the outside of the thylakoid membrane through the ATPase complex. Some transmembrane ATPases also work in reverse, harnessing the energy from a proton gradient, using the flux of ions across the membrane via the ATPase proton channel to drive the synthesis of ATP.

Additional Information:
-There are several different types of transmembrane ATPases, which can differ in function, structure, and in the type of ions, they transport. The different types include:
- F-ATPases, which are found in mitochondria, chloroplasts, and bacterial plasma membranes where they are the prime producers of ATP, using the proton gradient generated by oxidative phosphorylation.
-V-ATPases which are primarily found in eukaryotes and they function as proton pumps that acidify intracellular compartments and, in some cases, transport protons across the plasma membrane. They are also found in bacteria.

Note:
The extensive stromal membrane system is called the thylakoid system or lamellar system. Chlorophyll molecules and light-absorbing accessory pigments are embedded in it.
- It mainly consists of several cylindrical discs, called grana. Adjacent grana are connected together by a system of tubular membranes.
- Stroma is a metabolic center where Carbon dioxide fixation and synthesis of nucleic acids, sugars, starch, fatty acids, and some chloroplast protein take place.