The nucleus is
a membrane bounded organelle which is found on Eukaryotic cells. It is also the
largest cellular organelle in animal cells and is 5µm in diameter. Mostly the
cells are uni-nucleate, and some cells may have more than one nuclei. But there
are few types of cells which lack a nucleus. Ex: mammalian red blood cells. The
nucleus carries the hereditary information or the genetic material of the cell
which are arranged within the chromosomes. These chromosomes are formed by the
long linear DNA molecules and different types of proteins including Histone.
The DNA and protein complex which makes the chromosomes is called chromatins.
Each eukaryotic cell has a specific number of chromosomes. Ex: typical human
cell has 46 chromosomes.
The double membranes around the nucleus is called the
nuclear envelope. The nuclear envelope consists of phospholipids which is
impermeable to larger molecules. The two membranes are separated by a space of
20-40nm. The function of this envelope is to maintain the shape of the nucleus
and to regulate the molecules which flows in and out of the nucleus. The outer
membrane of the nuclear envelope is attached with the Rough Endoplasmic
Reticulum. There are pores along the nuclear envelope which provides a channel
to transport molecules across the nuclear envelope. They are known as nuclear
pores and are about 100nm in diameter. This helps in the transportation of molecules
such as RNA, different proteins, carbohydrates, and some DNA. Within the
nucleus there is a viscous liquid called nucleoplasm which is also called
Karyoplasm. It is mainly composed of water, different enzymes, dissolved salts
and some suspended organic molecules. The nucleolus and the chromosomes are
kept intact within the nucleus by the nucleoplasm. In animal cells a mesh
structure is present which is called the nuclear lamina that provides the
support to the envelope.