Nuclear Envelope

The nuclear envelope is the double membrane that encloses the nucleus, keeping its genetic material separate from the cytoplasm ¹. It is present in plant and animal cells.

      nuclear envelope
   ┌─────┐  ╭─────────╮  ┌─────┐
   │  ═══╪══│  DNA    │══╪═══  │  pores let substances
   │     │  │ ○ ○ ○   │  │     │  pass in and out
   └─────┘  ╰─────────╯  └─────┘
                nucleus

Why the Envelope Matters

• Compartmentalisation — the envelope protects the DNA and keeps the reactions that act on it away from the rest of the cell.
• Pores — gaps in the envelope allow substances such as RNA and proteins to move between the nucleus and the cytoplasm.
• Two membranes — the envelope consists of an inner and an outer membrane, unlike the single cell membrane.

Bacterial cells have no nuclear envelope, so their circular DNA lies free in the cytoplasm ¹ — one of the features that separates the prokaryote kingdom from the plant, animal, fungus and protoctist kingdoms.

Related

• Nucleus - Organelle bounded by this envelope.
• DNA - Genetic material protected inside it.
• Cytoplasm - Compartment outside the envelope.
• Cell - Structural unit containing the nucleus.
• Biology - Cambridge IGCSE life-science area.