Functions of the cell nucleus

introduction

The nucleus (nucleus) forms the largest organelle of eukaryotic cells and is located in the cytoplasm, separated by a double membrane (nuclear envelope). As the carrier of genetic information, the cell nucleus contains genetic information in the form of chromosomes (DNA strand) and thus plays an essential role in inheritance. Most mammalian cells have only one nucleus; this is round and has a diameter of 5 to 16 micrometers. Certain cell types, such as muscle fibers or specialized cells in bone, can have more than one nucleus.

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Functions of the cell nucleus

The cell nucleus is the most important organelle in a cell and makes up 10-15% of the cell volume. The nucleus contains most of a cell's genetic information. In humans, in addition to the cell nucleus, the mitochondria also contain DNA ("mitochondrial DNA"). However, the mitochondrial genome only codes for a few proteins, which are mainly needed in the respiratory chain for energy production.

Read more about this at:

• Mitochondria
• Cell respiration in humans (respiratory chain)

Illustration of a cell nucleus

1. Nucleus -
   Nucleus
2. Outer nuclear membrane
   (Nuclear envelope)
   Nucleolemma
3. Inner nuclear membrane
4. Nuclear corpuscles
   Nucleolus
5. Nuclear plasma
   Nucleoplasm
6. DNA thread
7. Nuclear pore
8. Chromosomes
9. cell
   Celulla
   A - nucleus
   B - cell

You can find an overview of all images from Dr-Gumpert under: medical images

Storage of genetic information

As a store of deoxyribonucleic acid (DNA), the cell nucleus is the control center of the cell and regulates many important processes of cell metabolism. The cell nucleus is essential for a cell to function. Cells without a nucleus usually cannot survive. An exception to this are the nucleated red blood cells (Erythrocytes). In addition to regulatory functions, the tasks of the cell nucleus include the storage, duplication and transmission of DNA.

The DNA lies in the form of a long, strand-like double helix in the cell nucleus, where it is compactly packed into chromosomes with core proteins, the histones. Chromosomes consist of chromatin, which only condenses into microscopically visible chromosomes during cell division. Every human cell contains 23 chromosomes in duplicate, which are inherited from both parents. Half of the genes in a cell come from the mother, the other half from the father.

The cell nucleus controls metabolic processes within the cell using messenger molecules made from RNA. The genetic information codes for proteins that are responsible for the function and structure of the cell. If necessary, certain sections of the DNA, called genes, are transcribed into a messenger substance (messenger RNA or mRNA). The mRNA that is formed leaves the cell nucleus and serves as a template for the synthesis of the respective proteins.

Think of DNA as a kind of encrypted language made up of four letters. These are the four bases: adenine, thymine, guanine and cytosine. These letters make up words, each made up of three bases, called codons.

Each codon codes for a certain amino acid and thus forms the basis for protein biosynthesis, because the sequence of bases of the genes is translated into a protein by connecting the respective amino acids. The entirety of this encrypted information is called the genetic code. The specific sequence of the bases makes our DNA unique and determines our genes.

But not only bases are involved in the structure of DNA. The DNA consists of nucleotides in a row, which in turn consist of a sugar, a phosphate and a base. The nucleotides represent the backbone of the DNA, which is in the form of a helical double helix. In addition, this strand is further condensed so that it fits into the small nucleus of the cell. Then one also speaks of chromosomes as a form of packaging for DNA. With each cell division, the complete DNA is copied so that each daughter cell also contains the completely identical genetic information.

Chromosomes used to package DNA

A chromosome is a certain form of packaging of our genetic material (DNA) that is only visible during cell division. DNA is a linear structure that is far too long to fit into our cell nucleus in its natural state. This problem is solved by various space-saving spirals of the DNA and the incorporation of small proteins around which the DNA can continue to wrap. The most compact form of DNA are the chromosomes. Under the microscope, these appear as rod-shaped bodies with a central constriction. This form of DNA can only be observed during cell division, i.e. during mitosis. Cell division, in turn, can be divided into several phases, whereby the chromosomes are best represented in the metaphase. The normal body cells have a double set of chromosomes, which consists of 46 chromosomes.

Further information on cell nucleus division is available at: Mitosis

RNA as part of the cell nucleus

The RNA describes the ribonucleic acid, which has a similar structure to the DNA. However, this is a single-strand structure that differs from DNA in terms of individual components. In addition, the RNA is also much shorter than the DNA and has several different tasks compared to it. In this way, the RNA can be divided into different RNA subgroups that perform different tasks. Among other things, the mRNA plays an important role during cell nucleus division. Like tRNA, it is also used in the production of proteins and enzymes. Another subgroup of RNA is rRNA, which is a component of the ribosomes and is therefore also involved in the production of proteins.

Protein synthesis

The first step in protein biosynthesis is the transcription of the DNA into mRNA (transcription) and takes place in the cell nucleus. A strand of DNA serves as a template for a complementary RNA sequence. Since no proteins can be produced within the cell nucleus, the mRNA formed has to be released into the cytoplasm and brought to the ribosomes, where the actual synthesis of the proteins takes place. Within the ribosomes, the mRNA is converted into a sequence of amino acids that are used to build proteins. This process is known as translation.

Before the messenger RNA can be transported out of the nucleus, it is first processed in many steps, that is, certain sequences are either appended or cut out and put back together again. This means that different protein variants can arise from one transcript. This process enables humans to produce a large number of different proteins with relatively few genes.

Replication

Another important function of the cell, which takes place in the cell nucleus, is the duplication of DNA (Replication). In a cell there is a constant cycle of build-up and breakdown: old proteins, pollutants and metabolic products are broken down, new proteins have to be synthesized and energy has to be produced. In addition, the cell grows and divides into two identical daughter cells. Before a cell can divide, however, all of the genetic information must first be duplicated.This is important because the genome of all cells within an organism is absolutely identical.

Replication takes place at a precisely defined point in time during cell division in the cell nucleus; both processes are closely linked and are controlled by certain proteins (Enzymes) regulated. First, the double-stranded DNA is separated and each single strand serves as a template for the subsequent duplication. To do this, various enzymes dock on the DNA and complement the single strand to form a new double helix. At the end of this process, an exact copy of the DNA has been created, which can be passed on to the daughter cell when it divides.

However, if errors occur in one of the cell cycle phases, various mutations can develop. There are various types of mutations that can occur spontaneously during different phases of the cell cycle. For example, if a gene is defective, it is called a gene mutation. However, if the error affects certain chromosomes or chromosome parts, then it is a chromosome mutation. If the chromosome number is affected, it then leads to a genome mutation.

The topic could also be of interest to you: Chromosome aberration - what does it mean?

Nuclear pores and signaling pathways

The double membrane of the nuclear envelope has pores that serve the selective transport of proteins, nucleic acids and signal substances out of and into the nucleus.

Certain metabolic factors and signal substances reach the nucleus through these pores and influence the transcription of certain proteins there. The conversion of genetic information into proteins is strictly monitored and is regulated by many metabolic factors and signal substances, one speaks of gene expression. Many signaling pathways that take place in a cell end in the nucleus and influence the gene expression of certain proteins there.

Nuclear body (nucleolus)

Inside the nucleus of eukaryotic cells is the nucleolus, the nuclear body. A cell can contain one or more nucleoli, and cells that are very active and divide frequently can contain up to 10 nucleoli.

The nucleus is a spherical, dense structure that can be clearly seen under the light microscope and is clearly delimited within the cell nucleus. It forms a functionally independent area of ​​the core, but is not surrounded by its own membrane. The nucleolus consists of DNA, RNA, and proteins that lie together in a dense conglomerate. Maturation of the ribosomal subunits takes place in the nucleolus. The more proteins are synthesized in a cell, the more ribosomes are required and therefore metabolically active cells have several nuclear bodies.

Function of the nucleus in the nerve cell

The nucleus in a nerve cell has a variety of functions. The nucleus of a nerve cell is located in the cell body (Soma) together with other cell components (organelles), such as the endoplasmic reticulum (ER) and the Golgi apparatus. As in all body cells, the cell nucleus contains the genetic information in the form of DNA. Due to the presence of DNA, other body cells are able to duplicate themselves via mitosis. However, nerve cells are very specific and highly differentiated cells that are part of the nervous system. As a result, they are no longer able to double up. However, the cell nucleus takes on another important task. Among other things, the nerve cells are responsible for the excitation of our muscles, which ultimately leads to movement of the muscles. Communication between nerve cells and between nerve cells and muscles takes place via messenger substances (Transmitter). These chemical substances and other important life-sustaining substances are produced with the help of the cell nucleus. Not only the cell nucleus but also the other components of the soma play an important role. In addition, the cell nucleus controls all metabolic pathways in all cells, including nerve cells. To do this, the cell nucleus contains all of our genes, which, depending on their use, can be read and translated into the required proteins and enzymes.

You can find more information about the peculiarity of the nerve cell at: Nerve cell