nukleointivaihe

Nukleointivaihe, also known as the nucleolar organizer region (NOR), is a specific region within the chromosomes of eukaryotic cells that is responsible for the production of ribosomes, the cellular machinery responsible for protein synthesis. The NOR is characterized by the presence of tandem repeats of a specific DNA sequence, which is transcribed into ribosomal RNA (rRNA). This rRNA is then processed and assembled with ribosomal proteins to form the ribosomal subunits.

The NOR is a crucial component of the nucleolus, a substructure within the nucleus of eukaryotic cells. The nucleolus is where ribosome biogenesis occurs, involving the transcription of rRNA genes, their processing, and the assembly of ribosomal subunits. The NOR is typically located on the short arms of acrocentric chromosomes, such as chromosomes 13, 14, 15, 21, and 22 in humans.

The number and size of NORs can vary among different species and cell types. In humans, there are approximately 300-500 NORs per cell, and they are distributed across multiple chromosomes. The activity of NORs can be visualized using techniques such as silver staining or fluorescence in situ hybridization (FISH), which reveal the nucleolar organizing regions as distinct, brightly stained spots within the nucleus.

NORs play a critical role in cell division and differentiation, as they are involved in the regulation of ribosome production and protein synthesis. Dysregulation of NOR activity has been linked to various diseases, including cancer and neurodegenerative disorders. Understanding the structure and function of NORs is therefore essential for advancing our knowledge of cellular biology and developing targeted therapies for related diseases.