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.
• Nucleolus: a dense, darker region (one or more per nucleus) with no membrane. It makes ribosomal RNA (rRNA) and assembles it with proteins into ribosome subunits.
• Nucleoplasm: the fluid inside the nucleus.
Functions
• stores the genetic information in DNA and protects it
• site of DNA replication before cell division
• site of transcription, in which DNA is copied into mRNA, which then leaves through the pores to be translated on ribosomes
• makes ribosomes (in the nucleolus)Cells that make a lot of protein, such as pancreatic cells, often have a large nucleolus and many nuclear pores. Mature red blood cells in mammals have no nucleus, so they cannot make new proteins.
• 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.
• Nucleolus: a dense, darker region (one or more per nucleus) with no membrane. It makes ribosomal RNA (rRNA) and assembles it with proteins into ribosome subunits.
• Nucleoplasm: the fluid inside the nucleus.
Functions• stores the genetic information in DNA and protects it
• site of DNA replication before cell division
• site of transcription, in which DNA is copied into mRNA, which then leaves through the pores to be translated on ribosomes
• makes ribosomes (in the nucleolus)Cells that make a lot of protein, such as pancreatic cells, often have a large nucleolus and many nuclear pores. Mature red blood cells in mammals have no nucleus, so they cannot make new proteins.