Cell Nucleus Definition
The cell nucleus is a specialized structure that occurs in most cells and contains the majority of the cell’s genetic material in the form of multiple linear DNA molecules organized into structures called chromosomes.
It is a membrane-enclosed organelle within a cell that has a membrane around it and contains chromosomes. The nucleus is where RNA is made from the DNA in the chromosomes.
Cell Nucleus Structure
The cell nucleus is a membrane-bound organelle that contains the genetic material of the cell. It has two major functions: storing the cell’s hereditary material, or DNA, and coordinating the cell’s activities, which include growth, protein synthesis, and cell division.
The main structures making up the nucleus are the nuclear envelope, nucleoplasm or nucleus sap nuclear matrix, chromatin, and nucleolus.
The nuclear envelope is a double membrane that encloses the entire organelle and isolates its contents from the rest of the cell. It separates the fluid inside the nucleus, called nucleoplasm, from the rest of the cell.
The space between the two membranes is called perinuclear space and is continuous with the endoplasmic reticulum lumen. Nuclear pores perforate this envelope allowing for the exchange of materials between nuclear plants, nuclear fluid, and cytoplasm.
Chromatin is a complex of DNA and proteins that makeup chromosomes. It condenses to form visible chromosomes during mitosis or meiosis. Nucleolus is a membrane-less organelle within the nucleus that manufactures ribosomes – structures responsible for protein synthesis in cells.
During interphase when a nucleus is not dividing, a structure called a nucleolus becomes visible. In fact, it is usually considered one of the most prominent features within a nucleus.
The function of Cell Nucleus
The cell nucleus is a specialized structure that occurs in most cells of eukaryotic organisms. It has two major functions: to store the cell’s DNA and to coordinate the cell’s activities, including growth, metabolism, protein synthesis, and reproduction. The nucleus serves as the repository of genetic information and as the control center of the cell.
DNA replication, transcription, and RNA processing all take place within the nucleus. The nuclear envelope separates the contents of the nucleus from the cellular cytoplasm. It is a double-layered membrane that is riddled with holes called nuclear pores.
The nucleolus is another prominent structure found in the nucleus. It is often seen as a distinctly dense body and is sometimes referred to as a sub-organelle. The nucleolus is enriched with tandem repeats of rDNA (regions of DNA that encode rRNA or ribosomal RNA).
The major role of the nucleolus, therefore, is the synthesis of rRNA and the assembly of ribosomes – which are responsible for protein synthesis in cells.
Animal Cell Nucleus
The nucleus is a large organelle found in eukaryotic organisms, including animal cells. It stores the cell’s hereditary material or DNA and coordinates the cell’s activities, which include intermediary metabolism, growth, protein synthesis, and reproduction (cell division).
The nucleus occupies about 10% of a cell’s volume and is the most prominent feature of the cell. Most of the nuclear material consists of chromatin, which is the unstructured form of the cell’s DNA that will organize to form chromosomes during mitosis or cell division.
The nucleus has two primary functions: to store the cell’s DNA and maintain its integrity and to facilitate its transcription and replication. The nucleolus is another prominent structure found in the nucleus.
It is enriched with tandem repeats of rDNA (regions of DNA that encode rRNA or ribosomal RNA) and synthesizes rRNA while assembling ribosomes – the protein synthesis machinery of the cell.
While animal cells have only one nucleus per cell, there are exceptions such as slime molds and Siphonales group algae that have multiple nuclei per cell. In contrast, simpler one-celled organisms like bacteria and cyanobacteria do not have a nucleus. All their information and administrative functions are dispersed throughout their cytoplasm.
Plant Cell Nucleus
The plant cell nucleus is a membrane-bound organelle that contains the DNA of the cell. It is responsible for storing the cell’s hereditary material or DNA, which contains all of the instructions for how to make proteins for the cell and control cell functions.
The nucleus coordinates the cell’s activities, including intermediary synthesis and reproduction (cell division). The spherical nucleus occupies about 10 percent of a plant cell’s volume, making it the most prominent feature of a plant cell.
The plant cell nucleus appears spherical and is located centrally in the cytoplasm. It constitutes 10% of a plant cell’s volume and is surrounded by a double-layered membrane or nuclear envelope, within which nucleolus, chromatin material, and karyoplasm are present.
The nuclear envelope protects the DNA from reactions occurring in the cytoplasm. However, it can communicate with the cytoplasm via a nuclear pore complex that allows the selective import and export of materials within the plant cell.
Both animal cells and plant cells have nuclei suspended in their cytoplasm in the middle of each respective cell. While there are subtle differences between animal and plant nuclei, their main purpose and general activities remain similar.
Other Examples of Cell Nuclei
The cell nucleus is a membrane-bound organelle found in eukaryotic cells that contains genetic material in the form of DNA.
Eukaryotic cells usually have a single nucleus, but some cell types have multiple nuclei. The best-known nuclear body is the nucleolus, which is involved in the assembly of ribosomes.
The nucleus contains nearly all of the cell’s DNA, is surrounded by a network of fibrous intermediate filaments, and is enveloped in a double membrane called the nuclear envelope. The nuclear envelope separates the fluid inside the nucleus, called the nucleoplasm, from the rest of the cell.
Besides plants and animals, there are countless variations to these two general schemes in nature. Some cells merge, creating large cells with multiple nuclei in each cell.
Many organisms have specialized cells with unique nuclei that perform specific functions. For example, muscle cells contain many nuclei to support their high energy demands. Fungal hyphae can contain hundreds or thousands of nuclei within a single cell.
In addition to these examples, other structures within cells resemble nuclei but are not true nuclei. For example, bacterial cells have a region called the nucleoid that contains their genetic material but is not enclosed by membrane-like eukaryotic nuclei.