The nucleus

With the exception of mature red blood cells and platelets, every eukaryotic cell contains a nucleus (8 μm diameter) (Fig. 3.2.1). The nuclear matrix or nucleoplasm contains two complete copies of the genomic DNA, which in non-dividing cells (interphase) is packaged into chromosomes. The chromosomal complement or karyotype of normal humans is 22 homologous pairs of chromosomes plus the sex chromosome pair XY in males and XX in females. The nuclear envelope consists of a double-layer membrane separated by the periplasmic space. The outer nuclear membrane forms a continuum with the rough endoplasmic reticulum (ER) and the periplasm forms a continuum with the ER lumen. The structure of the nucleus is determined by the nuclear lamina, a dense network of rod-like lamin neuro-filaments that forms associations between DNA molecules and the inner membrane.

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