NUCLEUS

NUCLEUS

 The nucleus is a large organelle of a cell. It is a central depository of genetic material.   This separates genetic material from cytoplasm.

 The nucleus is double membrane organelle. Which has an outer membrane, an inner membrane, and periplasm space. The nuclear outer membrane is in continuity with the endoplasmic reticulum. Which serves as a site for protein synthesis. Nucleus, however, is the site for chromatin storage and gene regulation. Here transcription. tRNA synthesis and rRNA synthesis occur. 

MATRIX

Nuclear Matrix, along with chromatin consist of many proteins that are associated with ribosome synthesis, as well as histone proteins, and many proteins that are associated with gene regulation. It has rRNA, tRNA, hnRNA, nucleotide, and regulatory proteins.

The nuclear membrane is composed of phospholipids and proteins. 

Nucleus 

Nuclear Pore Complex

 Nucleus has a special structure, which is known as the nuclear pore Complex that is associated with the transfer of molecules across the nuclear membrane. 

Nuclear Pore Complex is composed of 30 to 50 types of protein it is 125 million Daltons in molecular weight. It is a large Complex that is associated with the transfer of the ribosome to the cytoplasm

Most of the polar molecules are passively transported through the nuclear pore Complex. 

NUCLEAR PORE COMPLEX

The nonpolar components are either selectively or actively transported across the nuclear pore complex.  RNA and ribosomes require special signal tags for their transport across the nuclear pore complex

Structurally, NPC has a cytoplasmic domain, inter membrane domain, and a nucleoplasmic domain. The nucleoplasmic domain is called the nuclear basket that has many spokes that connect the nuclear basket to the median domain. The Nuclear Pore Complex recognizes the signal tag for the transport of molecules.

Chromatin present in the nucleus is associated with the Lamin protein, which is underneath the nuclear membrane. Lamin proteins are fibrous proteins that are associated with the inner nuclear membrane with another protein, Emarin, and LBR. Thus, Lamin acts as an anchor to the chromatin fibers. 

Interphase chromatin is divided into heterochromatin and euchromatin, where euchromatin is highly extended and associated with transcription. However, heterochromatin is highly compact and appears darker in staining processes. 

NUCLEOLUS 

Another dominant structure present in the nucleus is the nucleolus.  Which is associated with nucleolar organizing region (NOR), which are present on chromosomes 13, 14, 15, 21, and 22. These chromosomes carry tandem repeats of rRNA genes. These consist mainly of 18S rRNA, 5.8S rRNA, and 28S rRNA. The rRNA in the nucleolus constitutes the fibrillar component of the nucleolus. While protein that involved in the packaging of rRNA into the ribosome form the granular component. The nucleolus is the site where rRNA is processed and packaged into ribosomal subunits. Thus, the small subunit of the ribosome and the large subunit of the ribosome are synthesized in the nucleolus. These are then transported through the NPC to the cytoplasm, where they are actively involved in the synthesis of protein. Another rRNA, which is also required for the synthesis of ribosome is 5S rRNA, which is present on chromosome number 1, which is present outside the NOR.

FUNCTIONS

It is a depository of genetic material. 

It is the site of gene expression. 

It is the site of ribosome synthesis. 

It acts as the control center of the cell.

The nucleus is the site of gene regulation.

It is the site of the ribosome subunit synthesis and storage.

Post-transcriptional modification of RNA occurs in the nucleus.