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| 1. |
What are heterocyst |
| Answer» Heterocyst are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as Nostoc punctiforme, Cylindrospermum stagnale, and Anabaena sphaerica. They fix nitrogen from dinitrogen (N2) in the air using the enzyme nitrogenase, in order to provide the cells in the filament with nitrogen for biosynthesis. Nitrogenase is inactivated by oxygen, so the heterocyst must create a microanaerobic environment. The heterocysts\' unique structure and physiology require a global change in gene expression.For example heterocysts:Produce three additional cell walls, including one of glycolipid that forms a hydrophobic barrier to oxygen Produce nitrogenase and other proteins involved in nitrogen fixationDe-grade photosystem II, which Produces oxygen .Up-regulate glycolytic enzymes.Produce proteins that scavenge any remaining oxygen.Contain polar plugs composed of cyanophycin which slows down cell-to-cell diffusion. | |