nucleolus organization

Definition

Target type: biologicalprocess

A process that is carried out at the cellular level which results in the assembly, arrangement of constituent parts, or disassembly of the nucleolus. [GOC:dph, GOC:jid, GOC:jl, GOC:mah]

The nucleolus is a prominent structure within the nucleus of eukaryotic cells that plays a crucial role in ribosome biogenesis. Its formation and organization are tightly regulated processes involving a complex interplay of proteins, RNAs, and DNA.

The nucleolus is not membrane-bound but instead forms through the association of specific chromosomal regions, known as nucleolar organizer regions (NORs), which contain the genes encoding ribosomal RNA (rRNA). These genes are transcribed by RNA polymerase I, producing pre-rRNA transcripts that are processed and assembled into ribosomal subunits.

The initial step in nucleolus formation is the recognition and clustering of NORs. These regions are characterized by repetitive DNA sequences that bind specific proteins, including nucleolin and fibrillarin. These proteins act as scaffolding elements, facilitating the assembly of NORs into a nucleolar precursor body.

As pre-rRNA transcripts are synthesized, they associate with ribosomal proteins, forming pre-ribosomal particles. These particles, along with other nucleolar components, assemble into the dense fibrillar center (DFC) of the nucleolus. The DFC is the site of pre-rRNA processing, where the transcripts are cleaved and modified to produce mature rRNAs.

Surrounding the DFC is the dense fibrillar component (DFC), a region enriched in pre-ribosomal particles and processing factors. The DFC is further surrounded by the granular component (GC), where ribosomes undergo final assembly and maturation.

The organization of the nucleolus is dynamic and responsive to cellular needs. For example, during periods of active protein synthesis, the nucleolus expands and its activity increases to meet the demand for ribosomes. Conversely, during periods of stress or cell cycle arrest, the nucleolus may shrink or even disappear.

The intricate process of nucleolus organization is essential for the proper functioning of eukaryotic cells. Disruptions in nucleolar structure or function can lead to a wide range of cellular defects, including impaired ribosome biogenesis, protein synthesis, and cell growth. Therefore, understanding the molecular mechanisms underlying nucleolus organization is crucial for understanding cell biology and disease pathogenesis.'
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Proteins (1)

Compounds (2)