The nucleus is an organelle found in eukaryotic cells that houses the cell's genetic material. It was first observed by Anton van Leeuwenhoek in the 17th century and further described by Robert Brown in the 19th century. The nucleus is surrounded by a double membrane called the nuclear envelope and contains chromatin fibers, nucleoplasm, and one or more nucleoli. It controls cell functions and stores the cell's genetic information in the form of DNA.

1. NUCLEUS
By,
K.ThangaMallika,
I M.Sc., Microbiology

2. INTRODUCTION
• The nucleus was the first organelle to be
discovered.
• It was first observed by ANTON VAN
LEEUWENHOEK (1632 - 1723).
• In more detail in 1831 by Scottish Botanist
ROBERT BROWN was observed and named it
as “aerola” or “nucleus”.

3. OCCURENCE
• OCCURRENCE - Found in all eukaryotic cells of
plants and animals.
• EXCEPTIONS - Mature sieve tubes and
erythrocytes.
• Prokaryotes (Bacteria) lack true nucleus.
• POSITION - Usually at the centre but it can
change its position according to the metabolic
state.
• NUMBER - Mononucleate , Binucleate and
Polynucleate cells.

4. • SHAPE AND SIZE : Its shape is related with the
shape of the cell. It may be spherical or
ellipsoidal.
• Its size is related with number of the
chromosomes. Eg: small in haploid cell and large
in diploid cell.
• Its size also depends upon the volume of the
cell, amount of DNA, proteins and metabolic
phase of the cell.

6. ULTRA STRUCTURE
• Larger organelle of the cell.
• Approximately 6 micrometer in diameter.
• Occupies about 10% of total volume of cell.
DIFFERENT PARTS:
1. Nuclear Envelope
2. Nuclear lamina
3. Nucleoplasm
4. Chromatin fibres
5. Nucleolus

8. 1. NUCLEAR ENVELOPE :
• Nuclear membrane, outer most covering of
nucleus.
• It acts as a barrier to prevent macro molecules
from diffusing freely between nucleoplasm and
cytoplasm.
• It contains 2 cellular membranes:
1.Inner membrane 2.Outer membrane .

9. • They are arranged parallel to one another .
• The space between 2 membranes – perinuclear
space.
• The outer membrane is continuous with the
membrane of golgi body, mitochondria,
Endoplasmic Reticulum, also studded with
ribosomes.
• Nuclear membrane is not continuous but broken
at regular intervals, these broker areas are known
as Nuclear Pores.

10. • Inner nuclear membrane : 5 to 10 mm thick. It
contains Proteins. It acts as a main dwelling for
many inner nuclear membrane pores.
• Outer nuclear membrane : perinuclear space
occupies 10 to 500 mm diameter. It continues
with Endoplasmic reticulum, studded with
ribosomes .
• It also contains fibres, lipid droplets, crystalline
deposits.

11. a. NUCLEAR PORES:
• Nuclear membrane is not continuous but broke
at regular intervals, these broken areas are
known as Nuclear pores.
• They can vary in number and it depends on
species and types of the cell. Eg: Mammalian cell
has 3000 to 4000 pores.
• The pores are circular structure and it consists
of Annuli.

12. 2. NUCLEAR LAMINA:
• Mostly composed of lamina proteins, which
synthesized in the cytoplasm and later
transported into nucleus.
• Lamin: Fibrous protein providing structural
function and for the cell nucleus.
• The lamin may be involved in the functional
organization of the nucleus.
• They may play a role in assembly and
disassembly before and after mitosis.

14. 3. NUCLEOPLASM:
• The space between nuclear envelope and
nucleolus is filled by a transparent, semi solid
granular substance is known as nucleoplasm.
• It is composed of nucleo protien and contains
inorganic and organic substances.
• It is similar to cytosol.

15. 4. CHROMATIN FIBRES :
• Chromatin is a mass of DNA and proteins that
condense to form chromosomes during cell
division.
• Chromatin is an essential part of genetic
makeup of eukaryotic cells, by controlling
replication, cell function and storing genetic
information.
• The basic structure for chromatin if the
NUCLEOPLASM.

17. 5. NUCLEOLUS:
• It is composed of the main products of the
rRNA genes, as well as their proteins and
enzymes.
• It is a large spherical and acidophilic dense
granule.
• Size depends on the synthetic activities of
the cell.
• Malfunction can leads to several human
diseases.

18. FUNCTIONS
• The nucleus contains most of the cell nucleus in
the form of chromatin. The chromatin then
organize into chromosomes during cell division.
The chromosome contains a set number of genes
and it controls every single trait.
• It controls all the activities inside the cell such as
cell growth, metabolism, protein synthesis.
• It has instructions for making proteins and other
molecules.

19. THANK YOU