This article provides information about the Chemical Composition of Nucleus!
The nucleus contains mainly nucleoproteins composed of nucleic acid and proteins, besides enzymes and inorganic salts.
The following is the percentage of different components of nucleus of mammalian liver cells in interphase, determined by spectrophotometric analysis:
DNA 9% Residual protein 14%
RNA 1% other acidic proteins 65%
Histone protein 11%
[I] Nucleic acids:
These are the main constituents of nucleoproteins comprising about 15 to 30% of the dry weight of nucleus, mostly as DNA. RNA is in very small amount as 1-2% of dry weight occurring mainly in nucleolus.
These substances (DNA and RNA) are found associated with the proteins forming deoxyribonucleoprotein or ribonucleoprotein. The nucleolus contains 8 to 10% of RNA by dry weight and upto 90% acidic protein. The amount of DNA in the nucleus depends upon the number of chromosomes; the higher the chromosome number, the greater the DNA amount.
These may be either acidic or basic proteins. Basic protein contents are comparatively greater than acidic proteins and contain mainly histone and protamines, as nucleohistones and nucleoprotamines. Histones are characterized by the preponderance of amino acids—arginine, histidine and lysine, while protamines show mainly arginine.
The protamines are usually bounded with the DNA molecules by the salt linkage. The histone proteins are associated with the DNA by the ionic bonds. Acidic proteins (nonhistone proteins) in nuclei show the abundance of amino acids name у tryptophan and tyrosine.
These are the most important components of nucleus. Diphosphopyridine nucleotide synthetase is an important nuclear enzyme necessary for the synthesis of diphosphopyridine nucleotide (DPN) which is a coenzyme for protein synthesis. Besides, there are DNA polymerase, RNA polymerase (forming m-RNA) necessary for the synthesis of DNA.
Other enzymes present in the nucleus are nucleotide phosphorylase, nucleotide triphosphatase, NAD synthetase, adenosine diaminase, guanase, aldolase, enolase, 3- hosphoglyceraldehyde, dehydrogenase, pyruvate kinase, and ribonuclease necessary for the synthesis of RNA. The nucleus also contains ATP and acetyl Co-A, etc.
[IV] Inorganic contents:
These are present in minute quantities but are of great biological importance. The inorganic materials include salts of calcium, potassium, sodium, magnesium, phosphorus, iron and zinc. They may be both associated with proteins or with enzymes and related to the organization of chromosomes as metallic ions.