Nucleolus Chromosomes

Other Cell Structures. Recently other cell structures have been separated Golgi substance, nucleolus, chromosomes, mitotic apparatus, and secretory granules. The identification of some of these fractions is not certain, and therefore the association of specific enzymes with these structures cannot be made at this time. 

Nucleus The nucleus is separated from the cytosol by a double membrane, the nuclear envelope. The DNA is complexed with basic proteins (histones) to form chromatin fibers, the material from which chromosomes are made. A distinct RNA-rich region, the nucleolus, is the site of ribosome assembly. The nucleus is the repository of genetic information encoded in DNA and organized into chromosomes. During mitosis, the chromosomes are replicated and transmitted to the daughter cells. The genetic information of DNA is transcribed into RNA in the nucleus and passes into the cytosol where it is translated into protein by ribosomes. 

That the cytoplasmic nucleic acid is present in the mitochondria, the micro-eomes, and the non-sedimentable cell-sap is also known.117 The nuclear ribonucleic acid has been reported to be associated with the nucleolus and the chromosomes.118 It is known, moreover, that the ribonucleic acids of the different parts of the cell are biochemically distinct, since they become labeled with P32 at different rates.119 In liver cells, the nuclear ribonucleic acid is also chemically distinct from the cytoplasmic material, since the two differ in composition.120 It is clear, therefore, that ribonucleic acids prepared from whole cells are likely to be mixtures of various molecular species. 

A somewhat spherical or oblong body in most living cells. This nucleus contains the chromosomes, which, in turn, bear the genes of heredity. The nucleus also contains a nucleolus, or sometimes two or more nucleoli and a basic ground substance, the nucleoplasm. A nuclear membrane surrounds it on the outside, but this membrane is very porous, allowing materials to pass through rather freely. 

Nucleus 0.7-3 Surrounded by a double membrane (10 nm), containing pores (40-70 nm wide) flexible and contains cytologically distinguishable chromosomes. Nucleolus about 3 nm... 

Nucleolus. A spherical structure visible in the nucleus during interphase. The nucleolus is associated with a site on the chromosome that is involved in ri-bosomal RNA synthesis. 

The nucleus stores the cell s genetic information as DNA in chromosomes. It is bounded by a double membrane but pores in this membrane allow molecules to move in and out of the nucleus. The nucleolus within the nucleus is the site of ribosomal ribonucleic acid (rRNA) synthesis. 

The major components of the nucleus include the chromosomes, the nucleolus, the nucleoplasm, and the nuclear cortex. Chromosomes are made of DNA the nucleolus manufactures ribosomal components and the nucleoplasm is the fluid and filaments inside the nucleus. The nuclear cortex is a dense area on the inner face of the nucleus, which tethers the chromosomes in place when the cell is not undergoing division. 

The most characteristic feature of a eukaryotic cell, the nucleus, consists of a nucleoplasm surrounded by a double nuclear m mbrane pierced by nuclear pores. The nucleoplasm contains the (linear) chromosomes of the cell, which are organised into heterochromatin, which stains only a little, and euchromatin, which stains more densely. The most important euchromatic area is the nucleolus, in which ribosomes are formed (Fig. 1.2). 

The nuclear matrix. The lipid bilayers, the histones and other soluble proteins, and the DNA can all be removed from nuclei by exfracfion and enzymatic digestion. An insoluble residue, the nuclear matrix, is left. Largely protein in nature, this matrix is spread throughout the nucleus. Remnants of the membranes remain in the form of profeins that were in or along the bilayer. The nucleolus is clearly defined. The DNA appears to be bound to the nuclear matrix proteins. A specific 320-kb piece of a Drosophila chromosome has been mapped and used fo locate nontran-scribed scaffold (or mafrix) affachmenf regions of DNA bound to matrix proteins. These were found af intervals of 26-112 kb, fhe infervening loops confain-ing up to five or more A 120-kDa... 

The nucleus is the brain of the cell that contains all of the cell s genetic information. The chromosomes consist of chromatin, which is a complex of DNA and proteins. The chromosomes are tightly coiled to conserve space while providing a large surface area. The nucleus is the site of transcription of the DNA into RNA. The nucleolus is where ribosomes are made. There is at least one of these dark-staining bodies inside the nucleus of most eukaryotes. The nuclear envelope is two membranes separated by a narrow space. The envelope contains many pores that let RNA out of the nucleus. 

The nucleolus is a web of threads with no surrounding membrane, and is rich in RNA. The nuclear sap contains chromatin threads which, at mitosis, become more densely organized and are seen as chromosomes (DNA+proteins). The total length of DNA in a nucleus is about 1 m, made up of about 3X10 nucleotides each with a molecular weight of about 350. F. Sanger has compared the amount of information stored in this quantity of DNA to that available in a large library. 

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