Eukaryotes - Nucleus
Description:
The nucleus is also known as the director of the cell. It is the most important part of the cell which directs and controls all the cellular functions.
A nucleus is present in all the eukaryotes except mature RBCs, sieve tubes of phloem, tracheids and vessels of xylem.
Nulceus was first described by Robert Brown in 1831. Later Flemming gave the name chromatin to the contents of the nucleus which were stained by basic dyes.
Nuclear membrane
Also called nuclear envelope or nucelolemma.
It controls the nucelo-cytoplasmic interactions and exchange of materials.
The nuclear envelope consists two parallel membranes with a space in between which is called the perinuclear space. Perinuclear space forms a barrier between the materials present inside the nucleus and that of cytoplasm.
The outer membrane remains continuous with the endoplasmic reticulum and bears ribosomes on it.
A number of places are present in the nuclear membrane in which the two membranes fuse together and form pores.
Nuclear pores help in movement of RNA and proteins in both directions between the nucleus and the cytoplasm.
Nucleoplasm
- Transparent, semifluid, colloidal ground substance present inside the nuclear membrane.
- It acts as nuclear skeleton and helps in maintaining the shape of the nucleus.
- It contains the nucleolus and the chromatin.
Nucleolus
- Spherical structures present in the nucleoplasm.
- Remains associated with the nucleolar organizing region (NOR) of the nucleolar chromosome.
- Non-membrane bound structure.
- It is a site for active ribosomal RNA synthesis.
- Nucleoli are larger and more numerous in cells that are actively carrying out protein synthesis.
