Q.30 Nuclear pores present on nuclear envelope are enclosed by a circular structure called as
Answer: (2) Annuli
Nuclear pores on the nuclear envelope are enclosed by circular structures called annuli (plural of annulus), which together form the nuclear pore complex (NPC) regulating nucleocytoplasmic transport.
Option Analysis
Lamina (1) – Incorrect
Nuclear lamina is a meshwork of intermediate filament proteins (lamins) lining the inner nuclear membrane, providing structural support and anchoring chromatin, not enclosing pores.
Annuli (2) – Correct
Annuli are ring-shaped protein structures (~100 nm diameter) surrounding each nuclear pore where inner/outer membranes fuse; they anchor ~30 nucleoporins forming the NPC’s spoke-ring assembly for selective transport.
Granum (3) – Incorrect
Grana (singular granum) are stacks of thylakoids in chloroplast stroma maximizing photosynthetic surface area; unrelated to nuclear structures.
Vesicle (4) – Incorrect
Vesicles are membrane-bound sacs for intracellular transport (e.g., Golgi-derived); they do not enclose nuclear pores.
Nuclear pores annuli nuclear envelope represent the cell’s gateway system, with ~3000-4000 NPCs per mammalian nucleus facilitating 1 billion molecules/minute between nucleoplasm and cytoplasm.
Nuclear Pore Complex Anatomy
Each NPC spans a 9 nm channel through fused membranes, with annuli forming inner/outer rings, cytoplasmic filaments, and nuclear basket; FG-nucleoporins create selective barrier (small molecules diffuse, >40 kDa require Ran-GTP transport).
| Component | Location | Function |
|---|---|---|
| Annuli | Pore perimeter | Anchor NPC scaffold |
| Nuclear Lamina | Inner membrane | Structural support |
| Grana | Chloroplast thylakoids | Photosynthesis |
| Vesicles | Cytoplasm | Vesicular transport |
Exam Relevance
Critical for NEET Botany/GATE Life Sciences: Link annuli exclusively to nuclear pores (not lamina); essential for understanding gene expression in plant cells, relevant to Rajasthan’s biotech research.
