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Scientists Solve Decades Old Photosynthesis Puzzle With IISc–Caltech Study

Scientists Solve Decades-Old Photosynthesis Puzzle With IISc–Caltech Study

IISc and Caltech researchers uncover why photosynthesis uses only one electron path, solving a long-standing mystery.

Updated: 15 October 2025 23:00 IST

Scientists Solve Decades-Old Photosynthesis Puzzle With IISc–Caltech Study

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IISc and Caltech researchers reveal why photosynthesis favors one electron pathway over another

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Highlights

IISc and Caltech decode photosynthesis’s first step
Electrons move only through the D1 branch in PSII
Energy barrier blocks flow in the D2 branch

A decades-old question, the first steps of photosynthesis, has been addressed by scientists from the Indian Institute of Science (IISc) and the California Institute of Technology (Caltech). By the process, plants, algae, and bacteria turn sunlight into energy. In the studies of the reactions within Photosystem II (PSII), scientists trace out why electrons adhere to only one of two identical pathways. These findings open the door to how subtle molecular differences decide the direction of electron flow. This also provides a new glimpse that helps the design of artificial photosynthetic systems.

Scientists Discover Why Only One Pathway Powers Electron Flow in Photosynthesis

According to a joint IISc-Caltech study, electrons in PSII should theoretically move along both D1 and D2 branches. However, the study denoted that the D2 branch has a much higher energy barrier, making electron transfer nearly impossible. The researchers mapped the energy patterns by using molecular dynamics simulations and quantum mechanical models. They found that the D1 branch allows smoother and faster electron flow due to lower activation energy.

Moreover, the team identified that the surrounding protein environment and pigment placement favour the D1 branch. The resistance to electron movement in D2 was seen to be around 100 times higher. This states why only the D1 side works in natural photosynthesis.

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It may be possible to rewire this process by tweaking pigment arrangements or swapping certain molecules suggested by researchers. It helps to create artificial photosynthesis systems for clean energy. This is a breakthrough in bioenergy research, facilitating a comprehension of how nature captures sunlight so efficiently.

These insights could help to design next-generation solar-based fuel systems revealed by Professor Prabal K. Maiti from IISc. Caltech's Bill Goddard noted that while many mysteries remain, the research marks a major theoretical and experimental advance in understanding life's most essential energy process.

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