Question

What are phycobilisomes in cyanobacteria associated with?

Answer 1

Phycobilisomes:

1. Phycobilisomes are large antennae complexes found in cyanobacteria and red algae that receive and transfer light energy for photosynthesis.
2. These phycobiliprotein complexes absorb a huge amount of the visible spectrum, allowing organisms to boost their absorption capacity significantly.
3. In cyanobacteria, red algae, and glaucophytes, phycobilisomes are light-harvesting antennae of photosystem II. Green algae/plants lost it in their plastids (chloroplasts).
4. In the visible range of light, each phycobiliprotein has a unique absorption and fluorescence emission maximum. As a result of their presence and the specific arrangement within the phycobilisomes, light energy can be absorbed and transferred unidirectionally to photosystem II chlorophyll a.
5. In this way, the cells take advantage of light wavelengths that are inaccessible to chlorophyll (in the 500-650 nm range) and use their energy for photosynthesis.
6. This is especially beneficial deeper in the water column, because longer wavelength light is less transmitted and so less available to chlorophyll directly.
7. In an antenna-like structure, the geometrical arrangement of a phycobilisome is exceedingly attractive. It has a 95 percent energy transfer efficiency.