Nucleoplasm in the context of "Protoplasm"

The cytoplasm is all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell and contained within the nuclear membrane is termed the nucleoplasm. The main components of the cytoplasm are the cytosol (a gel-like substance), the cell's internal sub-structures, and various cytoplasmic inclusions. The cytoplasm is about 80% water and is usually colorless.

The cytosol or cytoplasmic matrix or groundplasm, remains after the exclusion of the cell organelles and cytoplasmic inclusions. Microscopically it is a highly complex, polyphasic system in which all resolvable cytoplasmic elements are suspended, including the larger organelles such as the ribosomes, mitochondria, plant plastids, lipid droplets, and vacuoles.

The nuclear pore complex (NPC), is a large protein complex giving rise to the nuclear pore. A great number of nuclear pores are studded throughout the nuclear envelope that surrounds the eukaryote cell nucleus. The pores enable the nuclear transport of macromolecules between the nucleoplasm of the nucleus and the cytoplasm of the cell. Small molecules can easily diffuse through the pores. Nuclear transport includes the transportation of RNA and ribosomal proteins from the nucleus to the cytoplasm, and the transport of proteins (such as DNA polymerase and lamins), carbohydrates, signaling molecules, and lipids into the nucleus. Each nuclear pore complex can actively mediate up to 1000 translocations per second.

The nuclear pore complex consists predominantly of a family of proteins known as nucleoporins (Nups). Each pore complex in the human cell nucleus is composed of about 1,000 individual protein molecules, from an evolutionarily conserved set of 35 distinct nucleoporins. The conserved sequences that code for nucleoporins regulate molecular transport through the nuclear pore. Nucleoporin-mediated transport does not entail direct energy expenditure but instead relies on concentration gradients associated with the RAN cycle (Ras-related nuclear protein cycle). In 2022 around 90% of the structure of the human NPC was elucidated in an open and a closed conformation, and published in a special issue of Science, featured on the cover. In 2024 the structure of the nuclear basket was solved, finalising the completion of the structure of the nuclear pore complex.

The nuclear lamina is a dense (~30 to 100 nm thick) fibrillar network inside the nucleus of eukaryote cells. It is composed of intermediate filaments and membrane associated proteins. Besides providing mechanical support, the nuclear lamina regulates important cellular events such as DNA replication and cell division. Additionally, it participates in chromatin organization and it anchors the nuclear pore complexes embedded in the nuclear envelope.

The nuclear lamina is associated with the inner face of the inner nuclear membrane of the nuclear envelope, whereas the outer face of the outer nuclear membrane is continuous with the endoplasmic reticulum. The nuclear lamina is similar in structure to the nuclear matrix, that extends throughout the nucleoplasm.