Nucleus

The nucleus, the largest organelle in eukaryotic cells,it is a membrane-bound structure that contains the genetic material of a cell.It is present in Eukaryotic organisms The plural of nucleus is nuclei. Not all cells have nuclei, but many cells, such as those in plants, fungi, animals, and protists, contain these structures.
The nucleus is surrounded by a structure called the nuclear envelope. This membrane separates nucleuoplasm,fluid present in the nucleus from the cytoplasm.Nuclear envelope  is not allow large molecules enter into the nucleus.The two nuclear membranes appear to fuse at the nuclear pores . which allows selected molecules i.e a specific set of membrane proteins, pores function as channels that regulate the movement of material between the nucleus and the cytosol .A nuclear envelope is made up of two membranes .An outer membrane and an inner membrane. Each membrane is composed of phospholipids arranged in a bilayer.The inner and outer membranes are separated by the perinuclear space.The outer nuclear membrane is continuous with the rough endoplasmic reticulum.Inner membrane facing Lamina called nuclear lamina which is a protein sheet that contributes to nuclear mechanical supports and function like replication and cell division.

Chromosomes are also present in the nucleus.Chromosomes contain DNA which provides the genetic information necessary for the production of other cell components and for the reproduction.DNA can be duplicated in the nucleus. This process is called replication and creates an identical copy of DNA. during cell division are chromosomes visible by light microscopy.Non dividing cells chromosome material is condensed that is called chromatin . Chromatin contains DNA,RNA and proteins. Proteins present in the chromatin is Histones.This histones package tightly with DNA is called nucleosomes.DNA is made up of DNA bases, Adenine, thymine, cytocine, and guanine.

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%
Enzymes present in the Nucleus:
Enzymes of general distribution fell into three classes: (a) Those present in low concentrations, if at all, in the nuclei—alkaline phosphatase, the nucleotide phosphatases) and β-glucuronidase. (b) Those present in nuclei in varying concentrations—esterase. (c) Those present in high proportions in most nuclei—adenosine deaminase, nucleoside phosphorylase, and guanase.
Diphosphopyridine nucleotide synthetase: is an important nuclear enzyme necessary for the synthesis of diphosphopyridine nucleotide (DPN) which is a coenzyme for protein synthesis. 
DNA polymerase :DNA polymerase is to make DNA from nucleotides, the building blocks of DNA.with cytosine along with guanine, and thymine along with adenine. 
RNA polymerase:RNA polymerase also known as DNA-dependent RNA polymerase, is an enzyme that produces primary transcript RNA.Forming m-RNA necessary for the synthesis of DNA.
Other enzymes present in the nucleus are 
Nucleotide phosphorylase:
nucleotide + phosphate nucleoside + alpha-D-ribose 1-phosphate
Nucleotide triphosphatase:
The enzymes are capable of enzymatically unwinding duplex RNA structures by disrupting the hydrogen bonds that keep the two strands together.

NTP + H₂O NDP + phosphate

NAD synthetase:
This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds as acid-D-ammonia (or amine) ligases (amide synthases).
ATP + deamido-NAD⁺ + NH₃ AMP + diphosphate + NAD⁺

Adenosine diaminase:
Adenosine deaminase also known as adenosine aminohydrolaseis an enzyme involved in purine metabolism.  
Guanase:
Guanase is also called as Guanine deaminase, guanine aminase, and guanine aminohydrolase is an aminohydrolase enzyme which converts guanine to xanthine.  
Aldolase:
An aldolase is an enzyme that performs an aldol reaction or its reverse .
Enolase:
it is found in cytoplasm and nucleus.
2-phospho-D-glycerate phosphoenolpyruvate + H₂O.
3-phosphoglyceraldehyde:
Dehydrogenase: It belonging to the group of oxidoreductases that oxidizes a substrate by a reduction reaction that transfers one or more hydrides (H⁻) to an electron acceptor, usually NAD⁺/NADP⁺ such as FAD or FMN.

Pyruvate kinase:It catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP, yielding one molecule of pyruvate and one molecule of ATP.
Ribonuclease: necessary for the synthesis of RNAthe degradation of RNA into smaller components. Ribonucleases can be divided into endoribonucleases and exoribonucleases. 
The nucleus also contains ATP and acetyl Co-A, etc.
Inorganic material present in the Nucleus:salts of calcium, potassium, sodium, magnesium, phosphorus, iron and zinc. which are associated with protein and enzymes.
Nucleic acids present in Nucleus:
15 to 30% of the dry weight of nucleus, mostly 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. 
Proteins present in the Nucleus: 
Histones which are made up of amino acids arginine, histidine and lysine. Protamines are the proteins which present along with Histones . protamine bounded with DNA by  salt linkages.