SiteGround
www.siteground.com
Web Hosting Services Crafted with Care!
BioScience.pk App
www.bioscience.pk
Put vital info into the palm of your hand.

STRUCTURE AND FUNCTION OF CELL NUCLEUS

Published in Cell Biology
Wednesday, 07 June 2017 17:29
In 1832 "Robert Brown" discovered nucleus. It is the essential part of the cell.
 
A definite nucleus is absent in prokaryotic cell. Instead of it a DNA molecules is present. It is called by “Prokaryotic cell". Ex: Bacteria.
 
Definite nucleus is present. It is cov­ered by nuclear membrane.
 
The position of a nucleus in the cell is definite. It occupies more or less central position. Now and then it is pushed to die periphery.
 
Number:
 
  1. Anurfeate: Nucleus is absent Ex: RBC of mammal
  2. Mononucleate: It is very common. Usually the cell contains a single nucleus
  3. Binucleate: Two nuclei are present. Ex: cells of cartilage.
  4. Poly nucleate: Three to many nuclei are present. In animals poly nucleate cell is called "Syncytial cell". Ex: Syncytial cell of osteoblast.
.
Shape:
 
It is usually oval. But its shape is dependent on the cell type.
 
  1. Cylindrical: Ex: Columunar epithelium.
  2. Horse shoe shape: Ex: Paramecium meganucleus.
  3. Tri lobed nucleus: Ex: WBC of mammals.
  4. Branched nucleus: Ex: Silk spining cell of insect larvae.
  5. Irregular nucleus: Ex: Glandular cell of insect.
 
Size:
 
The size of the nucleus varies with cell type . It is directly proportional to the amount of cytoplasm. "Hertwig" gave nucleo plasmic index.
 
nucleas cell nucleoplasmic index 17
 
Structure:
 
The nucleus will show.
 
  1. Nuclear membrane.
  2. Nucleo-plasm or karyolymph.
  3. Chromatin network.
  4. Nucleolus.
 
Nuclear membrane:
 
It is called nuclear envelope. It is 100 to 150 A°. The membr< nes are unit membranes. The outer membrane bears ribosomes, It is cor, nuous with endoplasmic reticulum.
 
Nuclear pores:
 
Nuclear membrane is not continuous. Here and there pores are present. Each pore is 500 to 800 A° in diameter. Each pore is covered by annulus membrane The pore and annulus will be called "Pore Complex". Because of ithese pores nucleoplasm and cytoplasm will be continuous.
 
nucleus cell structure function9
 
Nucleoplasm:
 
Below the nuclear membrane a transparent semifluid is present. It is granular. In this a chromatin network is present. It contains proteins, ions, enzymes, and nuclic acids. It is believed that nucleoplasm will take part in spindle formation.
 
Chromatin network:
 
In the nucleoplasm chromatin net work is present. In the inter phase nucleus the chromosomes are fine threads, and in the form of a network.
 
Euchromatin & Heterochromatin:
 
In the interphase nucleus the chromatin net work shows dark stained regions. They are called heterochromatin regions, Light stained regions are called euchromatin.
 
In 1928 "Hertz" defined heterochromatin as condensed chromatin part. The hetero-chromatin is two types.
 
a) Facultative-hetero-chromatin:
 
This is a temporary state of inactivation of chromatin. In which one chromosome of the pair will becomes hetero chromatin. Ex : In mammals the second X chromosome in the somatic cells of female will become hetero-chromatin, it is called ban* body.
 
b) Constitutive hetero-chromatin:
 
It is present permanently. It is present in both chromosomes of the pair. It is common in nucleolar organising chromosomes.
 
Hetero-chromatic regions genitically inactive. Now a days it is believed that it contains polygens, for the synthesis of tRNA and 5S RNA.
 
Functions:
 
  1. It gives protection to the genome.
  2. Helps in the reflection of DNA.
  3. During synaptic pairing in meiosis it attracts the homologous chromosomes.
Nucleolus:
 
It was discovered by "Fontana". In almost all the cells in the inter-phase nucleus, nucleolus is present. The number may be one or two. In some cases hundreds of nuclei will be present. Ex. Amphibian oocyte. The size of the nucleolus is depended upon the activity of the cell. They may be smaller or big.
 
nucleolus nucleus cell13
 
The nucleous shows two parts, a) Amorphous part, b) Filamentous part.
 
a) Amphorophous part contains four parts
 
  1. Granular zone
  2. Fibrillar zone
  3. Protenaceious part,
  4. Nucleolar associated chromatid.
 
Nucleous contains RNA, proteins and enzymes. It is formed with the help of nucleolar organising chromosome.
 
Functions:
 
  1. It is helpful in biogenesis of ribosomes.
  2. It plays a major role in mitosis.
 
Constitution of Nucleus:
 
It contains nucleo proteins, enzymes and inorganic salts. Low molecular weight proteins like histones, protamines are present. High molecular proteins contain tryptophan, tyrosine are constituent particles, DNA, RNA nuclei acids will be present. Salts of sodium, magnesium, calcium etc., some phospholipids are also present.
 
Functions of Nucleus:
 
  1. Nucleus plays a major role in the general metabolism of the cell
  2. It is helpful in the synthesis of ribosomes.
  3. It is helpful in the synthesis of RNA.
  4. It controls the synthesis of proteins.
  5. It is the seat of heredity.

Useful Sites

  • NCBI

    National Center for Biotechnology Information
  • LTO

    Lab Tests Online® by AACC
  • ASCP

    American Society for Clinical Pathology
  • ASM

    American Society for Microbiology
  • The Medical Library®

    Project of BioScience.pk

Sponsored Links

ASH Job Center
www.jobcenter.hematology.org
By American Society of Hemotology
SiteGround
www.siteground.com
Web Hosting Services Crafted with Care!
Daily Science
www.bioscience.pk
The Science News app that will get you to the breaking news.
Advertisement

Sponsored Links

ASH Job Center
www.jobcenter.hematology.org
By American Society of Hemotology
Daily Science
www.bioscience.pk
The Science News app that will get you to the breaking news.
Make money online!
www.adf.ly
Use a URL shortener service that pays.
Online Digital Library
www.bioscience.pk
Free Downloads Medical Books.
SiteGround
www.siteground.com
Web Hosting Services Crafted with Care!
BioScience.pk App
www.bioscience.pk
Put vital info into the palm of your hand.

Connect With Us

Contact Us

All comments and suggestions about this web site are very welcome and a valuable source of information for us. Thanks!

Tel: +(92) 302 970 8985-6

Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Website: https://www.bioscience.pk

Our Sponsors

Findeen.com

By using BioScience.pk you agree to our use of cookies to enhance your experience on this website.