Nucleus
The central processing unit of the cell, houses the basic unit of life; The nucleic acid. All the living cells have nucleus except mature RBCs. The structural properties differ between prokaryotes and eukaryotes.
Essential characteristics:
- It is a double membrane organelle in case of eukaryotes . Prokaryotes have nucleus without any membrane.
- Has a darkly stained region called the nucleolus that is a hub of newly transcribed ribosomal RNA required for the assembly of ribosomes.
- Although it is impermeable to large molecules, it has a nuclear pore complex aiding the transport of nuclear material across the membrane.
Composition:
- Genetic material: The chromatin material forms the major component of the nucleus. The chromosomes are the folded version of the genetic material, The DNA (deoxyribonucleic acid). The packing of DNA into complicated structure like chromosome is brought about by the basic histone and non-histone proteins.
- Nucleolus: It is the darkly stained region of the nucleus and consists of rRNA and DNA forming rRNA. Its basic function is the assembly of the ribosomes.
- Nuclear lamina: It is an internal organized meshwork made up of lamin proteins which provides mechanical strength to the nucleus.
- Other subnuclear bodies: Besides the chromosome and nucleolus, the nucleus also consists of structures called Cajal bodies, PML(Premyelocytic leukemia) bodies, splicing speckles, etc.
Functions:
- It houses and forms an isolated system for the genetic material of the cell.
- By virtue of the structurally complicated nuclear envelope, it regulates the outflow of transcribed RNA into the cytoplasm and inflow of transcription factors along with other regulatory proteins.
- The processing of mRNA into matured form occurs inside the nucleus which is the pre-requisite for formation of proteins.