Nucleus
The nucleus is an organelle in the eukaryotic cell. It is surrounded by a membrane and contains the genetic material. It is located in the cytoplasm of the cell.
Definition
Eukaryotic cells differ from prokaryotic cells in their cell nucleus, among other things. In eukaryotes, this is separated from the cytoplasm by a double layer, the membrane. The nucleus of prokaryotes, like bacteria , is not separated from the cytoplasm.
The cell nucleus contains the genetic material, which is in the form of chromosomes . Most cells have a nucleus. However, there are also some exceptions. After the fusion of myoblasts, so-called myotubes are formed, which contain several nuclei.
Human erythrocytes, on the other hand, do not have a nucleus after the cell has matured. Cell division occurs from mitosis to meiosis. Mitosis is the division of the cell nucleus. Meiosis describes the division of the diploid cell. As a result, each nucleus has a haploid set of chromosomes at the end.
Anatomy
The cell nucleus has a diameter of about 5 to 16 µm. It is surrounded by a membrane. This consists of two membranes that are close together. These are referred to as the inner and outer nuclear membranes. The outer membrane merges into the endoplasmic reticulum and is covered with ribosomes. The nuclear membrane borders the nuclear lamina.
This consists of lamins, i.e. proteins bound to specific nuclear membranes . They belong to the group of intermediate threads. They stabilize the cell nucleus and separate the chromosomes or chromatin from the inner nuclear membrane. The chromatin describes the arrangement of chromosomes and specific proteins.
The membrane is additionally equipped with nuclear pores. These serve the exchange of materials with the outer area of the cell nucleus. As a rule, these are mRNA and rRNA, the messenger RNA (ribonucleic acid) or ribonuclear RNA. This transport is actively controlled. Certain regulatory proteins are transported into the cell nucleus to start the first steps of protein biosynthesis, i.e. transcription. This involves the production of mRNA using DNA as a template.
In addition, so-called nucleoli or core bodies are located in the cell nucleus. They contain the genes of the rRNA. The ribosomal subunits are produced in these nucleoli. The finished ribosomes then enter the cytoplasm via the nuclear pores. The genetic material is present in the cell nucleus in the form of chromosomes, which together with certain proteins, the histones, form the chromatin.
Function
Protein biosynthesis begins in the cell nucleus. The genetic material, the DNA (deoxyribonucleic acid), is first unfolded in order to make it accessible for proteins. The DNA has certain regions, which are usually in front of the actual gene, the promoter. This is where the RNA polymerase binds.
It usually forms a whole complex with other proteins that increase the function of the polymerase or also disrupt it. Such proteins are called enhancers if they help the polymerase, or silencers if they hinder this process. When the polymerase is active, the DNA double strand is unfolded.
The polymerase then begins to run down one of the single strands of DNA and produce the mRNA. She skips the introns. A gene consists of exons, the coding DNA material, and introns, the non-coding DNA material. This process is then called splicing. This process is called transcription.
The mRNA is then transported to the endoplasmic reticulum via the nuclear pores. There, the mRNA is then transcribed into an amino acid sequence with the help of the ribosomes. The protein is created. Further modifications of the protein then follow, such as glycosylation in the Golgi apparatus.
Diseases
There are a variety of diseases that can arise from defects in the cell nucleus. In most cases, such diseases arise due to defective replication of the DNA in the cell nucleus or due to defective transcription.
An example is sickle cell anemia. This results in an incorrect exchange of a specific amino acid during protein biosynthesis. This causes the erythrocytes to have a crescent shape and function incorrectly.
In addition, problematic errors can occur during the splicing process. Nonfunctional proteins are made, which can then disrupt the entire biological process in the cell.
A defect in the replication of entire chromosomes is also possible. An example of this is Down syndrome. The patients have a third chromosome 21. This contains a gene that can lead to Alzheimer’s disease. This is because this gene is then present three times and increases the likelihood of Alzheimer’s disease.
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My passion for health and wellness started at a young age when I became interested in the connection between the food we eat and the way we feel. This fascination led me to study nutrition and dietetics in college, where I learned about the importance of a balanced diet and the impact of various nutrients on the body.