BRAINCAKEThe Nucleus
The nucleus is usually the largest organelle in a eukaryotic cell, about 10 µm across. It contains the cell's genetic material and controls the cell's activities by controlling which proteins are made.
Structure
• Nuclear envelope: a double membrane surrounding the nucleus. The outer membrane is continuous with the rough endoplasmic reticulum and may have ribosomes on it.
• Nuclear pores: large holes through the envelope, lined with proteins. They control the movement of molecules between the nucleus and cytoplasm. mRNA and ribosome subunits leave through them; nucleotides, enzymes and other proteins enter.
• Chromatin: DNA wound around histone proteins. It is spread out when the cell is not dividing, and condenses into visible chromosomes during cell division. Densely stained regions are called heterochromatin.
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Key terms in this lesson
- nuclear envelope
- The double membrane that surrounds the nucleus, perforated by nuclear pores.
- nuclear pore
- A channel through the nuclear envelope that controls the movement of molecules, such as mRNA, between the nucleus and cytoplasm.
More in Eukaryotic Cells
- Membrane Proteins
- Fluid Mosaic Model
- Eukaryotic Cells
- Protoplasm
- Mitochondria
- Centrioles
- Cytoskeleton
- Vacuoles
All 30 lessons in Eukaryotic Cells · All Edexcel AS-level Biology topics