Cell nucleus - structure, functions
Cell nucleus
Definition
It is a structure found in eukaryotic cells. It contains DNA, which is the genetic material responsible for the characteristics of a given organism and the processes related to inheriting the characteristics.
Most cells have one nucleus, but there are also some with several or even several hundred (e.g. skeletal muscle fibers).
Some mature cells do not have the nucleus because it has disappeared during their development (e.g. in erythrocytes).
Structure
Nuclear envelope - 2 membranes separating the interior of the nucleus from the cytosol
Nucleoplasm (karyolymph) - fluid that filling the nucleus; contains enzyme proteins and RNA; there is chromatin immersed in it.
Chromatin - made of DNA wrapped on histone proteins; forms chromosomes. It is divided into:
♥ euchromatin - loosely packed, genetically active
♥ heterochromatin - whipped, less genetically active
Nucleolus - the part of the chromatin that contains the genes encoding the rRNA; rRNA synthesis and the process of joining rRNA with proteins into ribosome subunits takes place here
Nuclear pore - protein complex situated in nuclear envelope; it is responsible for the transport of substances between the inside of the nucleus and the cytosol.
Chromosome - single molecule of DNA
Functions
♥ Controlling the course of most of the cell's life processes by controlling the synthesis of proteins. (Proteins are the building ingredient of cells and tissues and play an important role in their metabolism.)
♥ Reproduction and transmission of genetic material to cells and daughter organisms.
Gene expression
All the processes from RNA synthesis to protein synthesis.
Packaging DNA in cell nucleus 
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