Page 20 - Headlines Histology2024_Neat

• With EM, the nucleolus consists of a sponge showing dark materials of
granular (pars granulosa) and fibrillar (pars fibrosa) both form the
nucleonema which is ribonucleoprotein permeated by dispersed filaments of
DNA (pars amorpha).

• The primary function of the nucleolus is the synthesis of ribosomal RNA
(rRNA). The genes that code for rRNA are known as nucleolar genes that
lie along five different pairs of chromosomes.

Nuclear sap (karyolymph)

• The nuclear sap is a colloidal solution in which chromatins are suspended.
It helps in the movement of RNA (rRNA, tRNA, and mRNA) toward the
nuclear pores.

The cell cycle

• The cell cycle is the alternation between mitosis and interphase.
• The interphase includes three stages; first gap stage, synthesis stage and

second gap stage.
• The first gap stage (G1-stage) is the stage between the end of mitosis and

the synthesis stage (S-stage). During this stage the RNA and protein
synthesis occur and the cell volume is restored to its normal size.
• During the synthesis stage (S-stage) the actual amount of DNA is
duplicated. In the second gap (G2-stage) d-chromosomes are formed and
the cell begins to enter cell division.

Cell division (mitosis)

• The mitosis includes four different phases: prophase, metaphase, anaphase
and telophase.

Prophase

• Individualization of chromosomes.
• Initiation of mitotic spindle.
• Centriolar duplication

20