A nucleus in the human cell

What is a nucleus?

The nucleus is present in the cytoplasm of Eukaryotic cells. The nucleus is a spherical structure surrounded by a lipid bilayer -a two-layered, relatively permeable nuclear membrane. Large pores are also present in the nuclear membrane through which large molecules like RNA pass quickly. The nucleus encloses the genetic material. At nuclear pores, two layers are connected.

The space between the two folds of the nuclear membrane is known as a ‘perinuclear cistern or space. Inner the internal layer of the nuclear membrane, there is a thin Nucleus in the human cell.

The layer is the nuclear lamina, which provides structural support to the nucleus.

Who discovered the nucleus?:

Robert Brown, in 1831, discovered the nucleus. It was the very first organelle to be found.

Position of the nucleus:

Usually, only one nucleus is present in the cell center. Usually, one nucleus is present in each cell; in some cells, more than one nucleus (nucleoli) are present, and in some nucleus is absent.

Nuclear receptor

Nuclear receptors are ligand-regulated transcription factors activated by steroid hormones, estrogen, thyroid hormones, vitamins, and other lipid-soluble signals.

Ligands are lipid-soluble substances -hormones, fat-soluble vitamins, and xenobiotic hormones.

When a ligand binds with its specific nuclear receptor, regulation of gene expression occurs. It causes ‘conformational’ changes of the receptor that activates receptors, and up-or down-regulation of gene expression occurs.

Nuclear receptors directly control genomic DNA. In human beings, 48 Nuclear receptors are present.

Types of receptors:

Class I Nuclear receptors

Class II Nuclear receptors

Class III Nuclear receptors are a subgroup of type I and II.

Class IV Nuclear receptors

They regulate :

Embryonic development and adult homeostasis.

Nuclear receptors bind directly to DNA; they are ‘Transcription factors .’

Orphan receptors have no endogenous ligands. However, some receptors, e.g., FXR, LXR, and PPAR, bind multiple metabolic products, e.g., free fatty acids, bile acids, et. cetra.

CAR, PXR, and other nuclear receptors are xenobiotic sensors that increase Cytochrome P 450 enzymes.

Domains of nuclear receptors are

N-terminal

DNA binding domain DBD

Hing region

Ligand binding domain (LBD)

And C-terminal.

Mechanism of action of Nuclear receptor:

Class I Nuclear receptors (NR) are in the cytosol(cytoplasm). When a hormone binds with NR, it dissociates heat stroke proteins (HSP), dimerization, and translocation( active transport ) to the nucleus. In the nucleus, NR binds to a specific sequence of DNA known as ‘Hormone Response Element (HRE).

The Nuclear receptor DNA complex, in turn, recruits other proteins responsible for DNA transcription into mRNA. mRNA is

translated into protein-changing in cell function.

Class II receptors: located in the nucleus bound to DNA. For example, the Nuclear receptor for the thyroid hormone TR is converted to ‘RXR. When the hormone is absent, the TR binds with the Corepressor protein.

TR- Corepressor protein complex dissociates when the hormone comes, and free TR binds with the Coactivator protein.TR- Coactivator protein complex recruits some protein, e.g., RNA polymerase, that causes transcription of DNA into RNA and finally protein.

Structure

The nucleus comprises chromosomes supporting proteins (deoxyribonucleic acid) DNA on which genes are present.

Gene is a portion of DNA molecule that carries information for all the individual’s features and characteristics.

Under normal conditions, chromosomes appear as irregular clumps of dark material

known as ‘chromatin.’ Chromatin is the evidence of the presence of chromosomes.

However, the pair of chromosomes become apparent and visible during cell divisions.

In human beings, there are 46 chromosomes arranged in 23 pairs of chromosomes.

Twenty-two pairs are somatic chromosomes; one pair is sex chromosomes, and x y, or xx.

Nucleolus

The nucleus of a cell contains one or more nucleoli. In the nucleus, the nucleolus is present, the most dense part of the nucleus. It is rich in RNA. They are bluish in nature. The characteristic feature of the nucleolus is that they lack membrane. The nucleolus is not covered by any membrane. Other organelles have membranes.

The nucleoli are collections of large amounts of RNA and proteins in the cytoplasm without any membrane. The size of the nucleoli depends on the activity of the cell. When the cell synthesizes protein rapidly, the nucleolus becomes enlarged.

The nucleoli are very prominent in growing cells to synthesize large amounts of proteins.

The nuclei form or synthesize the nucleolus. Some specific DNA gene causes the synthesis of different types of RNA. Some RNA is stored in the nucleus, but most enter the cytoplasm through nuclear pores.

They synthesize RNA, which stimulates ribosomes, to stimulate protein synthesis.

Functions of nucleus

Provides a template for RNA synthesis.RNA migrates in the cytoplasm and causes protein synthesis.

Genes are responsible for the inheritance of species-specific features

The nucleus is responsible for cellular reproduction and the multiplication of cells.

Proteins, fat, and Carbohydrates are present in the cell membrane. When a protein attaches to a carbohydrate, glycoproteins are formed that play vital roles in the cells, like cell adhesion.

Disclaimer:

Although every precaution has been taken to verify the accuracy of the information contained herein, the author assumes no responsibility for any errors or omissions. No liability is assumed for damage resulting from using the information contained within.

Structure of a nucleus