A filamentous cyanobacterium performing oxygenic photosynthesis in an aquatic habitat is also capable of fixing atmospheric nitrogen. Which cellular adaptation enables this organism to fix nitrogen efficiently without inactivating the oxygen-sensitive enzyme nitrogenase?
- Isolation of nitrogenase within specialized thick-walled cells called heterocysts that lack oxygen-evolving photosystem IICevap
- BSynthesis of a protective cell wall composed of cellulose to completely prevent oxygen gas entry into all vegetative cells
- CSecretion of a protein capsid around the nuclear region to compartmentalize respiratory and nitrogen-fixing enzymes
- DDirect conversion of atmospheric nitrogen into nitrates within vegetative cells using Nitrosomonas enzymes
Cevap
Isolation of nitrogenase within specialized thick-walled cells called heterocysts that lack oxygen-evolving photosystem II
Nitrogenase is an enzyme that reduces atmospheric nitrogen to ammonia but is destroyed by molecular oxygen. Cyanobacteria overcome this by compartmentalizing nitrogenase inside specialized cells called heterocysts. These heterocysts develop thick walls that impede gas diffusion and inactivate Photosystem II, preventing oxygen generation while allowing nitrogen fixation to take place safely.
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Cyanobacterial cell specialization and heterocyst function
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