Cell Nucleus Structure and Function

Nucleus Structure and Function

• The main function of the nucleus is to control cell growth and reproduction by storing genetic information.
• During cell division, the nucleus splits into two identical nuclei, each with a complete copy of the genetic material.

Nuclear Envelope

• The nuclear envelope is a double membrane structure that surrounds the nucleus.
• The nuclear envelope is perforated with nuclear pores, which allow for the exchange of molecules between the nucleus and cytoplasm.
• The nuclear envelope has a perinuclear space located between the inner and outer membranes.
• The nuclear envelope contains approximately 3,000-4,000 nuclear pores in a typical mammalian cell.

Nuclear Pores and Transport

• Nuclear pores are large protein complexes that span the entire nuclear envelope, allowing for the exchange of molecules between the nucleus and cytoplasm.
• The main function of nuclear pores is to regulate the transport of molecules in and out of the nucleus.
• The central transport channel in nuclear pores is responsible for the selective transport of molecules.
• Importins and exportins are proteins that play a crucial role in the nuclear pore complex, facilitating the transport of molecules into and out of the nucleus.

Nuclear Interior and Components

• The nuclear interior is composed of nucleoplasm, also known as karyoplasm.
• The nuclear lamina is a protein network attached to the inner nuclear membrane.
• The nucleoplasm contains nucleoli, which are regions of RNA synthesis and ribosome assembly.
• The nucleoplasm also contains nuclear speckles, which are regions of RNA processing and splicing.

Nucleoli and Ribosome Synthesis

• Nucleoli are responsible for the synthesis of ribosomal RNA (rRNA) and the assembly of ribosomes.
• In humans, the genes for 5.8S, 18S, and 28S rRNAs are located in the nucleoli.
• At the beginning of mitosis, nucleoli are dispersed and reassemble during telophase.
• The size of nucleoli is determined by the amount of rRNA synthesis.

Ribosome Synthesis and Assembly

• Ribosomal proteins are synthesized in the cytoplasm and then transported to the nucleus for assembly into ribosomes.
• The 5S rRNA genes are located in the nucleoplasm, separate from the genes for 5.8S, 18S, and 28S rRNAs.

Mitosis and Nuclear Envelope

• During the prophase of mitotic division, the nuclear envelope dissolves, releasing the chromatin into the cytoplasm.