Question

I haven't been able to find any good order-of-magnitude estimates for how many photosystems (e.g. how many PSII complexes, how many PSI complexes) are in an average chloroplast (or perhaps per area of thylakoid membrane). Textbooks always just show a small area of membrane, and I'm interested to know whether there are say hundreds of complexes or millions. Is there any published data on this?

Answer 1

Photosystems II (PSII) and I (PSI) are multiprotein complexes found in the thylakoid membrane of chloroplasts. Each complex consists of multiple antenna proteins and hundreds of chlorophyll molecules, suggesting there are hundreds of thousands or even millions of complexes in an average chloroplast.

Step-by-step explanation:

Photosystems II (PSII) and I (PSI) are multiprotein complexes found embedded in the thylakoid membrane of chloroplasts. While there is no specific data on the exact number of photosystems present in an average chloroplast or per unit area of thylakoid membrane, each photosystem consists of multiple antenna proteins that contain a mixture of 300 to 400 chlorophyll a and b molecules, as well as other pigments like carotenoids. Therefore, it can be estimated that there are hundreds of thousands or even millions of PSII and PSI complexes within the thylakoid membrane of an average chloroplast.