Nucleolus, Biology

Assignment Help:

NUCLEOLUS

  • Discovered by Fontana and name given by Bowman.
  • It is naked structure that is attached to chromatin at specific point called nucleolar organiser region or NOR.
  • NOR is a type of heterochromatin.
  • Nucleolus known as ribosomal factory, ribosomal protein is synthesized in the cytoplasm.
  • There is normally one nucleolus with each set of chromosomes.
  • Somatic cells of man may have five nucleoli (on 13, 14, 15, 21, and 22 chromosomes) while oocyte of Amphibians have approximately 2000 nucleoli. Nucleus of onion cells have 4 nucleoli.
  • True nucleolus is also termed as Plasmosomes and they are stainable by acid dyes. Cell actively engaged in protein synthesis have large nucleolus. For example oocytes, neurons etc.
  • Nucleolus remains absent in sperm cell, muscles cell and blastomeres during cleavage.
  • Nucleolus contains following parts -

(1) Fibrous part - Central part of nucleolus composed of fibers called nucleonema. Nucleonema mainly composed of r-DNA and proteins.

(2) Granular part - Peripheral part of nucleolus composed of granules (r-RNA + proteins) which represents maturing ribosomes.

(3) Amorphous matrix or Pars amorpha - A proteinaceous matrix which contains both fibers and granules. r-RNA 5.8s, 18s and 28s are synthesized in nucleolus. Ribosomal protein is synthesized in cytoplasm. Organisation of r-RNA and protein to form ribosomes occurs in nucleolus. Completely formed ribosomes then move to cytoplasm through nuclear pores. Nucleolus also play important role in initiation of cell division.

1198_Nucleolus.png


Related Discussions:- Nucleolus

Valve replacement, Valve Replacement Replacement of the diseased valve...

Valve Replacement Replacement of the diseased valve is done. This is done biologic tissue valves or mechanical valves. Three types of biologic tissue valves are used. Aut

Define obligatory and facultative water excretion, Define Obligatory and Fa...

Define Obligatory and Facultative water excretion? i) Obligatory water excretion: The kidney is 'obligated' to excrete some water to rid the body of its daily load of urinary s

Becoming online tutor, how can i work with u as an online biology tutor?

how can i work with u as an online biology tutor?

Explain intensity of heart sound, Explain Intensity of heart sound? Int...

Explain Intensity of heart sound? Intensity of S 1, particularly M 1 depends on the position of the bellies of mitral leafets when the LV begins to contract since S 1 is loudes

Meat snack products, S n a c k Products Meat snacks such as curls; ...

S n a c k Products Meat snacks such as curls; chips are made from sliced, whole meat and comminuted meat. Extruded snacks are made from meat and non meat ingredients. Extru

Define about the environmental deficiency of iodine, Define about the Envir...

Define about the Environmental deficiency of iodine? The ultimate causative Factor is deficient intake of iodine. Iodine occurs in soil and sea as iodide, the ions of which arc

Enzymology, Ethylene glycol is a poison that causes about fifty deaths a ye...

Ethylene glycol is a poison that causes about fifty deaths a year in the United States. Treating people who have drunk ethylene glycol with massive doses of ethanol can save their

Explain some weight loss during breastfeeding, Explain some Weight Loss dur...

Explain some Weight Loss during breastfeeding? Some women may want to return quickly to their pre-pregnancy weight. It is important to remember that some women will lose more,

What treatment should be used for cardiac tamponade, Q. What Treatment shou...

Q. What Treatment should be used for cardiac tamponade? Percutaneous Pericardiocentesis Cardiac tamponade is an acute emergency and percutaneous pericardiocentesis must b

Teratogens, TER A T OGEN S - These are chemicals or drugs causin...

TER A T OGEN S - These are chemicals or drugs causing malformed foetus . The production of monsters or malformed foetus is called tertogeny or teratogenesis . Th

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd