Nucleolus+-+Animal


 * __NUCLEOLUS__**



http://www.sinauer.com/cooper/4e/videos/09-01_Nucleus.mov - click here for a video In the higher organisms a cell may be defined as “a nucleated mass of protoplasm of microscopic size.” Its two essentials, therefore, are: a soft jelly-like material, similar to that found in the ovum, and usually styled cytoplasm, and a small spherical body imbedded in it, and termed a nucleus. Some of the unicellular protozoa contain no nuclei but granular particles which, like true nuclei, stain with basic dyes. The other constituents of the ovum, viz., its limiting membrane and the denser spot contained in the nucleus, called the **nucleolus,** are not essential to the type cell, and in fact many cells exist without them. ====The Nucleolus is a prominent sub-nuclear structure that is not bound by a membrane and resides within the nuclear matrix. Though known to exist since the eighteenth century, the primary function of the nucleolus was not discovered until the 1960s. It is now been determined that nucleoli manufacture the subunits that combine to form ribosomes, the cell's protein-producing factories. Accordingly, the size of nucleoli depends upon the ribosomal requirements of the type of cell in which they are found. In cells that produce large amounts of protein, and thus call for significant numbers of ribosomes, the size of the nucleolus is considerable, sometimes occupying as much as 25 percent of the total volume of the nucleus.====

During the period between cell divisions, when the chromosomes are in their extended state, 1 or more of them (10 in human cells) have loops extending into a spherical mass called the nucleolus. Here are synthesized three (of the four) kinds of [|RNA molecules] (28S, 18S, 5.8S) used in the assembly of the large and small subunits of **ribosomes**. 28S, 18S, and 5.8S ribosomal RNA is transcribed (by [|RNA polymerase I]) from hundreds to thousands of tandemly-arranged **rDNA genes** distributed (in humans) on 10 different chromosomes. The rDNA-containing regions of these 10 chromosomes cluster together in the nucleolus. (In [|yeast], the 5S rRNA molecules — as well as transfer RNA molecules — are also synthesized (by [|RNA polymerase III]) in the nucleolus.) Once formed, rRNA molecules associate with the dozens of different ribosomal **proteins** used in the assembly of the large and small subunits of the ribosome. But all proteins are synthesized in the cytosol — and all the ribosomes are needed in the cytosol to do their work — so there must be a mechanism for the transport of these large structures in and out of the nucleus. This is one of the functions of the nuclear pore complexes. When seen, it looks like a dark spot in the nucleus.

Nucleolus -[|http://www.palmbeach.k12.fl.us/Multicultural/ESOLCurriculumDocs/Secondary/SciAnimalCell.pd]f The **Nucleolus** (also called **nucleole**) is a non-membrane bound structure[|[][|1]http://en.wikipedia.org/wiki/Nucleolus#cite_note-0] found within the [|nucleus] in which [|ribosomal RNA] is [|transcribed], and is composed of protein and nucleic acids. The nucleolus ultrastructure can be visualized through an [|electron microscope] while the organization and dynamics can be studied through [|fluorescent protein tagging] and fluorescent recovery after photobleaching ([|FRAP]). Malfunction of nucleoli can be the cause for several human diseases. The nucleolus is a part of the nucleus. Strictly speaking it is not an organelle as it does not have its own membrane. It appears as a dense region and can be seen using a light microscope (of course not on the sort of slides you make in school usually). The nucleolus is a region of high transcription, the production of RNA, and is particularly associated with the synthesis of ribosomal RNA. The nucleolus disappears during cell division as transcription cannot be performed on condensed chromosomes. The nucleolus is a prominent sub-nuclear structure that is not bound by a membrane and resides within the nuclear matrix. Though known to exist since the eighteenth century, the primary function of the nucleolus was not discovered until the 1960s. It is now been determined that nucleoli manufacture the subunits that combine to form ribosomes, the cell's protein-producing factories. Accordingly, the size of nucleoli depends upon the ribosomal requirements of the type of cell in which they are found. In cells that produce large amounts of protein, and thus call for significant numbers of ribosomes, the size of the nucleolus is considerable, sometimes occupying as much as 25 percent of the total volume of the nucleus. Definition: A small, typically round granular body composed of protein and RNA in the nucleus of a cell. It is usually associated with a specific chromosomal site and involved in ribosomal RNA synthesis and the formation of ribosomes.
 * name(s): nucleolus
 * location: roughly in centre of nucleus.
 * appearance: approximately spherical but with an ill-defined edge
 * size: about 1 micrometer in diameter
 * function: production of robosomal components
 * The nucleolus is a smaller version of the nucleus

=Nucleolus= Jump to: [|navigation], [|search][|Previous (Nucleic acid)][|Next (Nucleoside)] The **nucleolus** is contained within the cell nucleus. The **nucleolus** (plural //nucleoli//) is a large, distinct, spheroidal subcompartment of the nucleus of [|eukaryote] [|cells] that is the site of [|ribosomal RNA] (rRNA) synthesis and assembly of ribosomal subunits. A nucleoli sometimes is referred to as a "non-membraneous organelle" or "nuclear membraneless organelle" in the broader sense of the term [|organelle]; however, nucleoli lack a membrane and thus are not organelles in the more technical sense of structures that are separately enclosed within their own lipid membrane. Most [|plant] and [|animal] cells have one or more nucleoli, but some cell types do not have any. The nucleolus is a highly dynamic structure from which the components are dispersed at the onset of [|mitosis] and are reassembled at the end of cell division. This intricate body works in cooperation with other nuclear components to provide a valuable function for the cell. However, when this complex coordination in human cells is disrupted, such as by [|viral] infection, congenital [|mutations], or increased activity, several human [|diseases] can result.

Function** - Rich in RNA and is the site of the synthesis of ribosomes media type="youtube" key="vt7gGKJUOEM" height="344" width="425"
 * __Nucleolus__
 * Structure** - consists of densely packed chromosomes, protein and precursor RNA strands from which the subunits of ribosomes are formed.

The nucleolus is the prominent structure in the nucleus is the nucleolus. The nucleolus produces ribosomes, which move out of the nucleus and take poistions on the rough endoplasmic rticulum where they are critical in protein synthesis.

//The Nucleolus//
Within the nucleus are one or more nucleoli. The nucleolus is roughly spherical, and appears as a mass of densely stained granules and fibres under an electron microscope. It consists of nucleolar organizers. They are specialized regions of some chromosomes with multiple copies of genes for ribosome synthesis, along with a considerable amount of RNA and proteins representing ribosomes in various stages of production. An average, healthy cell can produce up to 10 000 ribosomes per minute.