Nucleus
Links exist between the nucleus and the extracellular microenvironment that direct cell fate. ~ American biologists Valerie Weaver & Russell Bainer
The nucleus serves as the control center of a cell, maintaining the integrity of a cell’s genes and their expression. The nucleus contains the nuclear genome, which holds most of a cell’s genetic material, though the mitochondrion and cytoplasm also hold genomes relevant to their operations.
As with a mitochondrion, a double membrane envelops the cell nucleus. Nuclear envelope proteins – nucleoporins – selectively allow molecules in and out of the nucleus. Proper functioning of these nuclear pore complexes is critical to maintaining cell health.
Amazingly, nucleoporins can manage over 1,000 molecules per second. Amino acid sequences within these proteins are optimized for efficiency in screening and transport. The physiochemical optimality of these sequences has been conserved evolutionarily from the early times of eukaryotes.
A nucleus has no membrane-bound sub-compartments but is organized for various operations. The best-known sub-nuclear body in the nucleus is the nucleolus, which is the site of ribosome assembly. A control center for cellular growth and health, the nucleolus takes up 25% of the nucleus. Malfunctioning nucleoli are a known cause of several human diseases.
