Cell nucleus

The cell nucleus is a membrane-bound organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The nucleus maintains the integrity of these genes and controls the activities of the cell by regulating gene expression.

Structure

The nucleus is surrounded by a double membrane called the nuclear envelope, which separates the contents of the nucleus from the cytoplasm. The nuclear envelope is perforated by nuclear pores that allow the transport of molecules across the nuclear envelope. The interior of the nucleus is filled with a gel-like substance called the nucleoplasm, which contains the chromatin and the nucleolus.

Nuclear Envelope

File:Nuclear Envelope.svg

Diagram of the nuclear envelope.

The nuclear envelope consists of two lipid bilayer membranes, an inner and an outer membrane. The outer membrane is continuous with the endoplasmic reticulum. The space between the two membranes is called the perinuclear space.

Nuclear Pores

File:Nuclear Pore Complex.svg

Structure of a nuclear pore complex.

Nuclear pores are large protein complexes that cross the nuclear envelope, allowing the transport of molecules such as RNA and proteins between the nucleus and the cytoplasm. Each pore is composed of multiple proteins known as nucleoporins.

Nucleoplasm

The nucleoplasm is the semi-fluid substance within the nuclear envelope. It is similar to the cytoplasm and contains dissolved ions, molecules, and a network of fibers that help maintain the shape of the nucleus.

Chromatin

Chromatin is the complex of DNA and protein found in the nucleus. It exists in two forms: euchromatin, which is less condensed and transcriptionally active, and heterochromatin, which is more condensed and transcriptionally inactive.

Nucleolus

File:Nucleolus.svg

Diagram of the nucleolus.

The nucleolus is a dense region within the nucleus where ribosomal RNA (rRNA) is synthesized and combined with proteins to form ribosomal subunits. These subunits are then transported out to the cytoplasm where they combine to form functional ribosomes.

Function

The primary function of the nucleus is to store and protect the cell's genetic material. It also regulates gene expression and mediates the replication of DNA during the cell cycle.

Gene Expression

The nucleus controls gene expression by regulating the transcription of DNA into RNA. This process is mediated by RNA polymerase and various transcription factors.

DNA Replication

During the cell cycle, the nucleus is responsible for the replication of DNA. This ensures that each daughter cell receives an identical set of genetic information.

Cell Cycle and Division

The nucleus plays a crucial role in the cell cycle, particularly during mitosis and meiosis. During mitosis, the nuclear envelope breaks down, allowing the chromosomes to be separated into two new nuclei. In meiosis, the nucleus undergoes two rounds of division to produce gametes with half the number of chromosomes.

Related pages

• Eukaryotic cell
• Chromosome
• DNA replication
• Gene expression
• Mitosis
• Meiosis