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Encyclopedia > Nucleolus
The nucleolus is contained within the cell nucleus.
The nucleolus is contained within the cell nucleus.
Schematic of typical animal cell, showing subcellular components. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles
Schematic of typical animal cell, showing subcellular components. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles

In cell biology, the nucleolus (plural nucleoli) is a sub-organelle of the cell nucleus, which itself is an organelle. A main function of the nucleolus is the production and assembly of ribosome components. The nucleolus is roughly spherical, and is surrounded by a layer of condensed chromatin. No membrane separates the nucleolus from the nucleoplasm. Image File history File links Diagram_human_cell_nucleus. ... Image File history File links Diagram_human_cell_nucleus. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... Image File history File links Biological_cell. ... Image File history File links Biological_cell. ... Schematic of typical animal cell, showing subcellular components. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ... The eukaryotic cytoskeleton. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... Schematic of typical animal cell, showing subcellular components. ... Cross section of cell with cytoplasm labeled at center right. ... Various organelles labeled. ... A centriole showing the nine triplets of microtubules. ... Cell biology (also called cellular biology or formerly cytology, from the Greek kytos, container) is an academic discipline that studies cells. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... Schematic of typical animal cell, showing subcellular components. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Chromatin is the complex of DNA and protein found inside the nuclei of eukaryotic cells. ... Similar to the cytoplasm of a cell, the nucleus contains nucleoplasm or nuclear sap. ...



Nucleoli are made of protein and ribosomal DNA (rDNA) sequences of chromosomes. The rDNA is a fundamental component since it serves as the template for transcription of the ribosomal RNA (rRNA) for inclusion in new ribosomes. Most plant and animal cells have one or more nucleoli, but some cell types do not have any. Since nucleoli carry out the production and maturation of ribosomes, large numbers of ribosomes are found inside them. In addition to ribosome biogenesis, nucleoli are believed to have other roles in cellular activity. Ribosomal DNA (rDNA) are sequences encoding ribosomal RNA. These sequences regulate amplification and transcription initiation and contain transcribed and nontranscribed spacer segments. ... A scheme of a condensed (metaphase) chromosome. ... A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... Ribosomal RNA (rRNA), a type of RNA synthesized in the nucleolus by RNA Pol I, is the central component of the ribosome, the protein manufacturing machinery of all living cells. ...


Nucleoli fragment during cell reproduction (they can no longer be seen in metaphase of mitosis, when the chromosome copies separate). After the daughter cells complete their separation, the fragments of nucleoli fuse together around the nucleolus organizer regions (NORs) of the chromosomes. An image of a newt lung cell stained with fluorescent dyes during metaphase. ... Mitosis divides genetic information during cell division. ... Nucleolus organizer region(NOR) is a region inside rDNA that nucleolus synthesis there. ...

Contents

Structure

Study of the structure of the nucleolus has mainly concentrated on its RNA (Ribonucleic acid) synthesis area. The nucleolus includes fibrillar centers (FC), dense fibrillar components (DFC), granular components (GC) and rDNA. Other components are interstices and chromatin inclusions. The nucleolus can be observed with the light microscope, and was much studied in the nineteenth century; its structure has more recently been clarified using the electron microscope. Ribosomal DNA (rDNA) are sequences encoding ribosomal RNA. These sequences regulate amplification and transcription initiation and contain transcribed and nontranscribed spacer segments. ... 1852 microscope Compound microscope made by John Cuff in 1750 A microscope (Greek: micron = small and scopos = aim) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. ... An electron microscope is a type of microscope that uses electrons as a way to illuminate and create an image of a specimen. ...


Fibrillar center (FC)

It is made up by a network of fine (4-5 nm thick) Fibrils. The shape of an FC is typically roughly spherical, with the diameter ranging from about 50nm to 1 μm. The number and size of FCs per nucleolus is variable, and changes with cellular activity and the need for ribosome production. Cells with lower cellular activity usually have fewer FC than others. Fibril is a fine fiber approximately 1 nm in diameter. ...


Dense Fibrillar Component (DFC)

This component is also made up by very fine (3-5 nm) and densely packed fibrils. DFCs usually surround FCs when they are present and form a meshwork. As this is particularly true for activated states, the amount of DFC roughly reflects the nucleolar engagement in ribosome biogenesis. Sometimes this meshwork occupies large areas of the nucleolus, occasionally interspersed with small FCs.


During S phase of cell cycle, the increase in upstream binding factor (UBF) association may be due to the increase in its ability to compete with the histones for binding to the rDNA. DNA replication. ... In molecular biology, an upstream transcription factor is a protein which binds to a cis-regulatory element (such as an enhancer or repressor sequence) upstream from a gene and either directly or indirectly affects the initiation of transcription. ... Schematic representation of the assembly of the core histones into the nucleosome. ... Ribosomal DNA (rDNA) are sequences encoding ribosomal RNA. These sequences regulate amplification and transcription initiation and contain transcribed and nontranscribed spacer segments. ...


Granular component (GC)

The granular component appears to consist of small granules with a diameter of about 15 nm. They typically form a mass surrounding the fibrillar complexes and embed the FCs and DFC. Thus a transition zone between DFC and GC can be observed. Although nucleolus is not membrane-bound, due to the presence of GC the border with the surrounding chromatin and nucleoplasm is usually distinct. A biological membrane or biomembrane is an enclosing or separating tissue which acts as a barrier within or around a cell. ...


Ribosomal DNA (r DNA)

rDNA is a set of tandemly-repeated genes coding for preribosomal RNA. Because these genes have the ability to initiate the formation of nucleoli during interphase, these segments of the chromosomes are called nucleolus organizer regions or NORs. In the human genome, there are tandem repeats of the r DNA sequence on the short arms of each of the two copies of chromosomes 13, 14, 15, 21 and 22. Ribosomal DNA (rDNA) are sequences encoding ribosomal RNA. These sequences regulate amplification and transcription initiation and contain transcribed and nontranscribed spacer segments. ... preribosomal RNA is a non-complete RNA that serve as the intermediate form during RNA biogenesis. ... This article does not cite any references or sources. ... Nucleolus organizer region(NOR) is a region inside rDNA that nucleolus synthesis there. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...


Functions

The main role of the nucleolus is considered to be ribosome biogenesis, since its fundamental component DNA codes for preribosomal RNA. Ribosome biogenesis, the process of making ribosomes, takes place both in the cell cytoplasm and in the nucleolus of eukaryotic cells. ... preribosomal RNA is a non-complete RNA that serve as the intermediate form during RNA biogenesis. ...


Additionally, recent research pointed out that the nucleolus is also responsible for the trafficking of various prominent small RNA species. The nucleolus helps them during their maturation process and route to their final cellular destination. Moreover, although nucleoli become invisible during cell division, more recent studies have found that they are involved in cell cycle regulation. Several of its non-traditional roles include interaction with viral components, the regulation of tumor suppressor and oncogene activities, signal recognition particle assembly, the modification of small RNA strands, the control of aging and modulating telomerase function. The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication. ... vaghhyyyyyyyyyyyyyyyyyyyyyyyyyyyy viral vaghela (shrewsbury, massachusetts) also know as vagh is the hot sexy lover of kinjal shah (houston, texas) ... A tumor suppressor gene is a gene that reduces the probability that a cell in a multicellular organism will turn into a tumor cell. ... An oncogene is a modified gene that increases the malignancy of a tumor cell. ... The signal recognition particle (SRP) is a protein-RNA complex that recognizes and transports specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes. ... Telomerase is an enzyme that adds specific DNA sequence repeats (TTAGGG in all vertebrates) to the 3 (three prime) end of DNA strands in the telomere regions, which are found at the ends of eukaryotic chromosomes. ...


See also

A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... Left: An RNA strand, with its nitrogenous bases. ... Discovered by Fox et al. ...

References

  • Olson, Mark O.J. (2004). The Nucleolus Georgetown, Texas : Landes Bioscience / Eurekah.Com. Kluwer Academic/Plenum Publishers. New York. ISBN 0-306-47873-0
  • Khadzhiolov, Asen A. (1985). The nucleolus and ribosome biogenesis Wien : Springer-Verlag. ISBN 3-211-81790-5
  • Thiry, Marc & Guy Goessens (1996). The nucleolus during the cell cycle Hong Kong : Springer ; Austin, Tex. : R.G. Landes Company. New York. ISBN 3-540-61352-8
  • Alberts, Bruce et al. (2002). The Molecular Biology of the Cell, 4th ed., Garland Science, 2002, ISBN 0-8153-3218-1, p.331-3.

External links

  • Nucleolus under electron microscope at cellnucleus.com
  • Nucleolus under electron microscope II at uni-mainz.de
  • Recent concerns about nucleolus at hgu.mrc.ac.uk
  • MeSH Cell+Nucleolus
  • Histology at BU 20104loa

  Results from FactBites:
 
biology - Nucleolus (122 words)
In biology, the nucleolus is, strictly speaking, a "suborganelle" of the cell nucleus, which is an organelle.
It is a consequence of ribosomal RNA (rRNA) synthesis: nucleolar organizers, special regions on some chromosomes that contain multiple copies of the genes encoding for rRNA (which is involved in protein biosynthesis), gather themselves in the same region where they transcribe the rRNA genes.
Thus it can be said the nucleolus consists basically of nucleolar organizers and the transcribed rRNA (plus associated proteins).
Cell (biology) - Facts, Information, and Encyclopedia Reference article (3708 words)
The drawing on the left highlights the internal structures of eukaryotic cells, including the nucleus (light blue), the nucleolus (intermediate blue), mitochondria (orange), and ribosomes (dark blue).
The drawing on the right demonstrates how bacterial DNA is housed in a structure called the nucleoid (very light blue), as well as other structures normally found in a prokaryotic cell, including the cell membrane (fl), the cell wall (intermediate blue), the capsule (orange), ribosomes (dark blue), and a flagellum (also fl).
Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle,(5) rough endoplasmic reticulum (ER), (6) Golgi apparatus, (7) Cytoskeleton, (8) smooth ER, (9) mitochondria, (10) vacuole, (11) cytoplasm, (12) lysosome, (13) centrioles
  More results at FactBites »

 
 

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