Nucleus how does it function

In these organisms, all of the cell's information and administrative functions are dispersed throughout the cytoplasm. The spherical nucleus typically occupies about 10 percent of a eukaryotic cell's volume, making it one of the cell's most prominent features. A double-layered membrane, the nuclear envelope, separates the contents of the nucleus from the cellular cytoplasm. The envelope is riddled with holes called nuclear pores that allow specific types and sizes of molecules to pass back and forth between the nucleus and the cytoplasm.

It is also attached to a network of tubules and sacs, called the endoplasmic reticulum, where protein synthesis occurs, and is usually studded with ribosomes see Figure 1. The semifluid matrix found inside the nucleus is called nucleoplasm. Within the nucleoplasm, most of the nuclear material consists of chromatin, the less condensed form of the cell's DNA that organizes to form chromosomes during mitosis or cell division.

The nucleus also contains one or more nucleoli, organelles that synthesize protein-producing macromolecular assemblies called ribosomes, and a variety of other smaller components, such as Cajal bodies, GEMS Gemini of coiled bodies , and interchromatin granule clusters. Chromatin and Chromosomes - Packed inside the nucleus of every human cell is nearly 6 feet of DNA, which is divided into 46 individual molecules, one for each chromosome and each about 1.

Packing all this material into a microscopic cell nucleus is an extraordinary feat of packaging. For DNA to function, it can't be crammed into the nucleus like a ball of string.

Instead, it is combined with proteins and organized into a precise, compact structure, a dense string-like fiber called chromatin. The Nucleolus - The nucleolus is a membrane-less organelle within the nucleus that manufactures ribosomes, the cell's protein-producing structures. Through the microscope, the nucleolus looks like a large dark spot within the nucleus.

A nucleus may contain up to four nucleoli, but within each species the number of nucleoli is fixed. After a cell divides, a nucleolus is formed when chromosomes are brought together into nucleolar organizing regions. During cell division, the nucleolus disappears. Some studies suggest that the nucleolus may be involved with cellular aging and, therefore, may affect the senescence of an organism.

It is composed of two ribosomal RNA subunits that wrap around mRNA to start the process of translation, a stage of protein synthesis. Protein synthesis consists of two stages: transcription and translation. The mRNA leaves the nucleus via nuclear pores and goes to the ribosome. Typically, a protein is synthesized within the ribosome and released inside the channel of the rough ER, where sugars can be added to it by a process called glycosylation before it is transported within a vesicle to the next stage in the packaging and shipping process: the Golgi apparatus.

One of the main functions of the smooth ER is in the synthesis of lipids. The smooth ER synthesizes phospholipids, the main component of biological membranes, as well as steroid hormones. For this reason, cells that produce large quantities of such hormones, such as those of the female ovaries and male testes, contain large amounts of smooth ER.

In addition to lipid synthesis, the smooth ER also sequesters i. The smooth ER additionally metabolizes some carbohydrates and performs a detoxification role in the liver, breaking down certain toxins. In contrast with the smooth ER, the primary job of the rough ER is the synthesis and modification of proteins destined for the cell membrane or for export from the cell.

For this protein synthesis, many ribosomes attach to the ER giving it the studded appearance of rough ER. The Golgi apparatus is responsible for sorting, modifying, and shipping off the products that come from the rough ER, much like a post-office.

The Golgi apparatus looks like stacked flattened discs, almost like stacks of oddly shaped pancakes. Like the ER, these discs are membranous.

The Golgi apparatus has two distinct sides, each with a different role. One side of the apparatus receives products in vesicles. These products are sorted through the apparatus, and then they are released from the opposite side after being repackaged into new vesicles. If the product is to be exported from the cell, the vesicle migrates to the cell surface and fuses to the cell membrane, and the cargo is secreted Figure 3.

Some of the protein products packaged by the Golgi include digestive enzymes that are meant to remain inside the cell for use in breaking down certain materials. The enzyme-containing vesicles released by the Golgi may form new lysosomes, or fuse with existing, lysosomes. A lysosome is an organelle that contains enzymes that break down and digest unneeded cellular components, such as a damaged organelle. A lysosome is similar to a wrecking crew that takes down old and unsound buildings in a neighborhood.

Lysosomes are also important for breaking down foreign material. For example, when certain immune defense cells white blood cells phagocytize bacteria, the bacterial cell is transported into a lysosome and digested by the enzymes inside.

As one might imagine, such phagocytic defense cells contain large numbers of lysosomes. Under certain circumstances, lysosomes perform a more grand and dire function. In the case of damaged or unhealthy cells, lysosomes can be triggered to open up and release their digestive enzymes into the cytoplasm of the cell, killing the cell. Watch this video to learn about the endomembrane system, which includes the rough and smooth ER and the Golgi body as well as lysosomes and vesicles.

What is the primary role of the endomembrane system? In addition to the jobs performed by the endomembrane system, the cell has many other important functions. Just as you must consume nutrients to provide yourself with energy, so must each of your cells take in nutrients, some of which convert to chemical energy that can be used to power biochemical reactions.

Another important function of the cell is detoxification. Humans take in all sorts of toxins from the environment and also produce harmful chemicals as byproducts of cellular processes. Cells called hepatocytes in the liver detoxify many of these toxins. Mitochondria consist of an outer lipid bilayer membrane as well as an additional inner lipid bilayer membrane Figure 3.

The inner membrane is highly folded into winding structures with a great deal of surface area, called cristae. It is along this inner membrane that a series of proteins, enzymes, and other molecules perform the biochemical reactions of cellular respiration. These reactions convert energy stored in nutrient molecules such as glucose into adenosine triphosphate ATP , which provides usable cellular energy to the cell.

Cells use ATP constantly, and so the mitochondria are constantly at work. Oxygen molecules are required during cellular respiration, which is why you must constantly breathe it in. One of the organ systems in the body that uses huge amounts of ATP is the muscular system because ATP is required to sustain muscle contraction. The fluid component of the nucleus is called the nucleoplasm. The plural form is nuclei.

Nuclear is the descriptive term that relates to a nucleus. Compare: nucleoid. The nucleus is absent in prokaryotes and the lack of this organelle is used as a basis to distinguish whether a cell is a prokaryote or a eukaryote. Only eukaryotes have a nucleus; prokaryotes lack a nucleus. However, prokaryotes have a region in their cell where the genetic material is located. This region is called a nucleoid. It is nucleus-like and not bound by a nuclear envelope that separates the genetic material from the cytoplasm.

The nucleus should not be confused with another cytoplasmic structure, the nucleolus. Both of them are present in eukaryotic cells. However, they differ in structure and function. The nucleus is a double-membraned organelle whereas a nucleolus is a round granular structure and not membrane-bound. Nevertheless, the nucleolus is found inside the nucleus. Thus, the nucleolus is one of the nuclear components and is sometimes classified as one of the nuclear bodies.

Apart from the nucleolus, the other components of the nucleus are chromatins chromosomes , nuclear bodies e. Cajal bodies and gems Gemini of Cajal bodies , polymorphic interphase karyosomal association PIKA domains, promyelocytic leukaemia protein PML bodies, splicing speckles, paraspeckles, perichromatin fibrils, and clastosomes , nuclear membrane, and nucleoplasm.

While the nucleus is largely involved in gene regulatory functions, the nucleolus functions primarily for the creation of ribosomes essential for protein synthesis.

In higher eukaryotes, the nucleolus is comprised of a fibrillary center involved in the transcription of the rDNA, the dense fibrillary component that contains the fibrillarin protein associated with rRNA processing, and the granular component that contains the nucleophosmin protein for ribosome biogenesis.

The nucleus structure is a double-membraned organelle of the eukaryotes. It has three main components: nucleolus and other chromatins chromosomes , nuclear bodies, nuclear matrix , nucleoplasm , and nuclear envelope. A complex of nucleic acids e.

During cell division , the chromatin condenses to become a chromosome. The basic structural unit of chromatin is a nucleosome. Each nucleosome is made up of a DNA segment wound around the histone protein cores.

The main function of chromatin is to package DNA into a smaller volume to fit into the cell. There are two major forms of chromatin: the euchromatin and the heterochromatin. The euchromatin is structurally loose to allow transcription and replication whereas the heterochromatin is more condensed and therefore less active. This extranuclear DNA, such as cpDNA in chloroplasts and mtDNA in mitochondria , occurs in multiple copies since there are several chloroplasts and mitochondria while there is usually just one nucleus inside a cell.

A nuclear body is defined as a non-membraned mostly proteinaceous structure in the nucleus. As already mentioned above, the nucleolus is regarded as one of the nuclear bodies and is most prominent.

It is characterized by its round granular appearance. Its function is largely for the synthesis of ribosomes, which in turn are one of the key players in protein synthesis. Other nuclear bodies are Cajal bodies and gems Gemini of Cajal bodies , polymorphic interphase karyosomal association PIKA domains, promyelocytic leukemia protein PML bodies, splicing speckles, paraspeckles, perichromatin fibrils, and clastosomes.

The nuclear matrix is analogous to the cytoskeleton in the cytoplasm of the cell. It is a fibrillar network that provides structural support to the size and shape of the nucleus. The nuclear matrix is more dynamic though compared with the cytoskeleton. It includes the nuclear lamina. The latter refers to the dense fibrous network juxtaposing the nuclear envelope. The nucleoplasm refers to the protoplasm of the nucleus just as the cytoplasm in the rest of the cell. The nucleoplasm is comprised of various materials e.

The fluid component of the nucleoplasm is called a nucleosol just as the cytosol to the cytoplasm. The nuclear envelope also called a nuclear membrane is the biological membrane that surrounds the nucleus. Similar to a cell membrane, the nuclear membrane is a bilipid layer. Thus, the nuclear membrane function is similar to a cell membrane as well in terms of regulating the entry and exit of materials.

The nuclear envelope has nuclear pores to control the movement of molecule s between the nucleoplasm and the cytoplasm. It is impermeable to large molecules. Thus, it separates the contents of the nucleus from the cellular cytoplasm and allows the entry of selected molecules.