Heterocysts

Definition

Heterocysts are specialized nitrogen-fixing cells found in some filamentous cyanobacteria. They create an anaerobic environment necessary for the activity of the enzyme nitrogenase.

5 Must Know Facts For Your Next Test

1. Heterocysts differentiate from vegetative cells when fixed nitrogen is scarce.
2. They possess thick cell walls that limit oxygen diffusion, protecting nitrogenase from oxygen.
3. Photosynthesis does not occur in heterocysts; instead, they rely on neighboring vegetative cells for carbohydrates.
4. Heterocysts are interconnected with other cells through microplasmodesmata, allowing nutrient exchange.
5. The differentiation process of heterocysts is regulated by several genes, including hetR and patS.

Review Questions

• What environmental condition induces the differentiation of heterocysts?
• Why do heterocysts have thick cell walls?
• How do heterocysts obtain the energy needed for nitrogen fixation?

Related terms

Cyanobacteria: Photosynthetic bacteria that can fix atmospheric nitrogen.

Nitrogenase: An enzyme that catalyzes the conversion of atmospheric nitrogen to ammonia.

Vegetative Cells: Regular photosynthetic cells in cyanobacteria that provide nutrients to heterocysts.