Nucleus

 TOPIC#13          NUCLEUS

NUCLEUS

     INTRODUCTION

               It is present mostly in center of nucleus and its slightly darker than cytoplasm and due to this property it discovered early.Prominent structure of cell consist of 10% of cell.

     DISCOVERY
               It is discovered early by Robert brown in 1838.Its early discovery was due to its prominence in many cells.

   SIZE 

         Its size is about 10 micrometer.

   COMPOSITION

              It is the most important organelle in the cell.it contain DNA and genetic material.

     STRUCTURE

      Some cells have one nucleus called as mono nucleate and those with two nucleus called as bi nucleate while cells with more than two nuclei are said to be multi nucleate .

     It contains 4 parts which we will explain in detail:

    1-NUCLEAR MEMBRANE

                       It is outer double membrane of nucleus which seperates nucleus from cytoplasm.

  The outer membrane is continous with the endoplasmic reticulum(RER) While inner membrane continous with nuclear materials.

This nuclear membrane contain pores called as nuclear pores made up of protein called as NUCLEOPOREIN.

The Nuclear membrane is chemically composed of lipid bilayer + protein.

 The space between nuclear membrane is called PERI NUCLEAR SPACE.

  Undifferenciated cells like egg have 30,000 pores while differenciated cells like RBC have only 3-4 pores.

2- NUCLEOLOUS:

           It is darkly stained body in nucleus non mebraneous may be one in number or more than 1.

  Its main function of synthesis of ribosomal RNA and its storage.

 it composed of two regions;

A- PERIPHERAL GRANULAR AREA;

             it composed of precursor of ribosomal units .

B-CENTRAL FIBRILLAR AREA:

           It consist of large molecular RNA and rDNA.

     Nucleolus appears during interphase and dissapears during cell division.

3-NUCLEOPLASM:

                Semifluid colloidal mixture of organic and inorganic salts act as cytoplasm of nucleus called as Nucleoplasm.

 It also contain Enzymes,proteins,Free nucleotides having no histone, and these all raw materials help in  DNA replication and RNA syntheis.

 Here mostly polymerase enzyme is present which help in DNA replication. 

I WILL EXPLAIN 4TH TOPIC CHROMOSOME PART IN DETAIL TOMMOROW IN ANOTHER BLOG.

IMPORTANT MCQS IN THIS TOPIC:

1-The size of nucleus is:

Answer:   10 MICROMETER

2-The prominent organelle of cell is:

Answer:  NUCLEUS

3-The nuclear pores are made up of:

Answer: PROTEIN

4-The nucleus consist of_perecent of cell:

Answer: 10%

5-In which organisms the nuclear membrane is absent;

Answer:   PROKARYOTES

6-Which part of nucleus provide site for synthesis of rRNA:

Answer:  NUCLEOLUS

7-The _ region of Nucleolous composed of precursor of ribosomal units:

Answer:   PERIPHERAL

8-The nuclear pores are made up of protein called as:

Answer: NUCLEOPOREIN

9-Which part of cell is called as brain of cell:

Answer: NUCLEUS

10-The free nucleotides in nucleoplasm are :

Answer; NON HISTONE

11-The differenciated cells of eukaryotic cells mostly contain_nuclear pores:

Answer: 3-4

12-The nucleoplasm is _ mixtrure:

Answer: COLLOIDAL

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