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The nucleolus (/ nj uː ˈ k l iː ə l ə s, ˌ nj uː k l i ˈ oʊ l ə s /; pl.: nucleoli /-l aɪ /) is the largest structure in the nucleus of eukaryotic cells. [1] It is best known as the site of ribosome biogenesis. The nucleolus also participates in the formation of signal recognition particles and plays a role in the cell's response to ...
One hypothesized function of the dots is as a 'nuclear dump' or 'storage depot'. [21] The nuclear bodies may not all perform the same function. Sp140 associates with certain bodies and appears to be involved in transcriptional activation. [22] ND10 nuclear bodies have been shown to play a major role in chromatin regulation. [23]
The nuclear matrix is also believed to be contained in the nucleoplasm where it functions to maintain the size and shape of the nucleus, in a role similar to that of the cytoskeleton found in the cytoplasm. [10] However, the existence and the exact function of the nuclear matrix remain unclear and heavily debated.
The nuclear pore complex (NPC) is a crucial cellular structure with a diameter of approximately 120 nanometers in vertebrates. Its channel varies from 5.2 nanometers in humans [14] to 10.7 nm in the frog Xenopus laevis, with a depth of roughly 45 nm. [15]
In fact, DNA analysis of these two types of domains have shown that many sequences overlap, indicating that certain regions may switch between lamina-binding and nucleolus-binding. [35] NADs are associated with nucleolus function. The nucleolus is the largest sub-organelle within the nucleus and is the principal site for rRNA transcription.
A few examples of RNPs include the ribosome, the enzyme telomerase, vault ribonucleoproteins, RNase P, hnRNP and small nuclear RNPs , which have been implicated in pre-mRNA splicing (spliceosome) and are among the main components of the nucleolus. [22]
The location of NORs and the nucleolar cycle in human cells. Nucleolus organizer regions (NORs) are chromosomal regions crucial for the formation of the nucleolus.In humans, the NORs are located on the short arms of the acrocentric chromosomes 13, 14, 15, 21 and 22, the genes RNR1, RNR2, RNR3, RNR4, and RNR5 respectively. [1]
For example, a transcription factor may be directed to a nucleus, where it can promote transcription of certain genes. In terms of protein synthesis, the necessary organelles are relatively near one another. The nucleolus within the nuclear envelope is the location of ribosome synthesis.