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A generic term for any member of a large class of proteins associated with nucleic acid molecules. Nucleoprotein complexes occur in all living cells and in viruses, where they play vital roles in reproduction and protein synthesis.
Classification of the nucleoproteins depends primarily upon the type of nucleic acid involved—deoxyribonucleic acid (DNA) or ribonucleic acid (RNA)—and on the biological function of the complex. Deoxyribonucleoproteins (complexes of DNA and proteins) constitute the genetic material of all organisms and of many viruses. They function as the chemical basis of heredity and are the primary means of its expression and control. Most of the mass of chromosomes is made up of DNA and proteins whose structural and enzymatic activities are required for the proper assembly and expression of the genetic information encoded in the molecular structure of the nucleic acid. See Deoxyribonucleic acid (DNA)
Ribonucleoproteins (complexes of RNA and proteins) occur in all cells as part of the machinery for protein synthesis. This complex operation requires the participation of messenger RNAs (mRNAs), amino acyl transfer RNAs (tRNAs), and ribosomal RNAs (rRNAs), each of which interacts with specific proteins to form functional complexes called polysomes, on which the synthesis of new proteins occurs. See Ribonucleic acid (RNA)
In simpler life forms, such as viruses which infect animal and plant cells and bacteriophages which infect bacteria, most of the mass of the viral particle is due to its nucleoprotein content. The material responsible for the hereditary continuity of the virus may be DNA or RNA, depending on the type of virus, and it is usually enveloped by one or more proteins which protect the nucleic acid and facilitate infections. See Bacteriophage, Chromosome, Nucleic acid, Virus
A typical human diploid nucleus contains 5.6 × 10-12 g of DNA. This DNA is arranged in 23 pairs of chromosomes differing in size and DNA content. The large number 1 chromosome, for example, contains 0.235 × 10-12 g of DNA, while the much smaller chromosome number 22 contains only 0.046 × 10-12 g. The DNA double-helix of chromosome 1 is actually 7.3 cm long, but this thin filamentous molecule is packaged to form a chromosome less than 10 micrometers long. The enormity of the packing problem can be appreciated from the fact that the average human contains about 100 g of DNA, and 0.5 g would reach from the Earth to the Sun! The reduction in size is largely due to interactions between the DNA and sets of small basic proteins called histones. All somatic cells of higher organisms contain five major histone classes, all of which are characterized by a high content of basic (positively charged) amino acids.
a complex consisting of a nucleic acid and a protein. Nucleoproteins are widespread in nature. Deoxyribonucleoproteins and ribonucleoproteins are distinguished according to the nucleic-acid component. Deoxyribonucleoproteins constitute the chromatin matter in the nucleus of all cells and are present in the bodies of spermatozoa. Basic proteins called histones are the main protein component of deoxyribonucleoproteins. Smaller basic proteins called protamines occur in the spermatozooa of some animals, mainly birds and fish. Histones and protamines at neutral pH carry a large positive charge, which ensures a strong electrostatic interaction with nucleic acids, which are negatively charged. Deoxyribonucleoproteins are believed to be distributed in the grooves of the double helix of deoxyribonucleic acid, where they stabilize the helical structure and regulate the matrix activity of DNA. Many viruses, informosomes, and ribosomes consist of ribonucleoproteins (seeINFORMOSOMES).
REFERENCESFinean, J. Biologicheskie ul’trastructury. Moscow, 1970. (Translated from English.)
Khimiia biologicheski aktivnykh prirodnykh soedinenii. Moscow, 1970.
I. B. ZBARSKII