In cell biology, the nucleus (pl. nuclei; from Latin or , meaning kernel) is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others have many.
Cell nuclei contain most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these chromosomes are the cell's nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, the control center of the cell. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm, and the nuclear matrix (which includes the nuclear lamina), a network within the nucleus that adds mechanical support, much like the cytoskeleton, which supports the cell as a whole.
Because the nuclear membrane is impermeable to large molecules, nuclear pores are required that regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be actively transported by carrier proteins while allowing free movement of small molecules and ions. Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes. Although the interior of the nucleus does not contain any membrane-bound sub compartments, its contents are not uniform, and a number of sub-nuclear bodies exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes. The best-known of these is the nucleolus, which is mainly involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA.
Usage examples of "cell nucleus".
In the middle of almost every cell is a smaller piece called the cell nucleus.
During reproduction, the helices separate, assisted by a special unwinding protein, each synthesizing an identical copy of the other from nucleotide building blocks floating about nearby in the viscous liquid of the cell nucleus.
The axon stretches so far from the cell body that it seems quite reasonable to assume it can no longer maintain active communication throughout its length with the cell nucleus —.
These genes are the mechanism by which information arriving at the cell nucleus is translated into instructions for the later synthesis of key structural proteins - that is, proteins which will eventually be inserted into the synaptic membrane so as to change its structure and shape.
In the place of the removed egg cell nucleus, you insert the nucleus of a somatic cell of the same (or, possibly, an allied) species, and then let nature take its course.
This here is an ordinary cell nucleus, although the number of chromosomes in it is somewhat higher than one would normally expect to find in a bacteria.
He claimed that, while they were essentially similar to earthly bacteria in structure, being based upon proteins, carbohydrates, and lipids, they had no cell nucleus and therefore their manner of propagation was a mystery.
When looking at physical bodies, we should be able to show in exact detail how organisms come to possess a repeating cell structure with identical DNA within each cell nucleus.
But the thing is, if the embryo is successfully brought to term, the result is an exact dupe of the subject who donated the original cell nucleus.