NUCLEUS
Nuclei usually have spherical or ovoid shape. The first are approximately 10 microns in diameter, the second are 20 microns. Nucleus keeps genetic (hereditary) information, which in confined in DNA. DNA can replicate. Its
replication precedes nucleus division, so daughter nuclei also receive
DNA. Nucleus division, in its turn, precedes cell division, and owing to this all daughter cells also have nuclei.
The nucleus is confined into the nuclear envelope and contains chromatin, nucleolus (or, several nucleoli) and nucleoplasm.
The nuclear envelope consists of two membranes. The outer membrane turns immediately into endoplasmic reticulum, and, like endoplasmic reticulum, can be dotted with ribosomes, where protein synthesis goes on. The nuclear envelope is pierced with nuclear pores. Exchange of various matters between the nucleus and the cytoplasm is carried out through the nuclear pores. For example, it can be going out of messenger RNA (mRNA) or ribosomal subunits into the cytoplasm. Or, it can be coming of ribosomal proteins, nucleotides and molecules regulating the activity of DNA, into the nucleus. The pores have a certain structure. This structure is the result of junction of the outer and inner membranes of the nuclear envelope. This structure regulates the transport of molecules through the pore.
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Supplementary information
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