2. INTRODUCTION
• The nucleus is a membrane-
enclosed organelle found
in eukaryotic cells.
• The nucleus (pl. nuclei) is derived
from Latin word nucleus or nuculeus which
means kernel or seed.
• The nucleus is a highly specialized
organelle that serves as the information
processing and administrative center of the
cell.
• This organelle has two major functions: it
stores the cell's hereditary material, or
DNA, and it coordinates the cell's activities,
which include growth, intermediary
metabolism, protein synthesis, and
reproduction (cell division).
3. • The spherical nucleus typically occupies about 10 percent
of a eukaryotic cell's volume, making it one of the cell's
most prominent features.
• Only the cells of advanced organisms, known
as eukaryotes, have a nucleus. Generally there is only
one nucleus per cell, but there are exceptions, such as
the cells of slime molds and the Siphonales group of
algae.
• Simpler one-celled organisms (prokaryotes), like the
bacteria and cyanobacteria, don't have a nucleus.
• In these organisms, all of the cell's information and
administrative functions are dispersed throughout the
cytoplasm.
4. STRUCTURE OF NUCLEUS
• The nucleus is the largest cellular organelle in animal
cells. In mammalian cells, the average diameter of the
nucleus is approximately 6 µm, which occupies about
10% of the total cell volume.
• The viscous liquid within it is called nucleoplasm (or
karyolymph), and is similar in composition to
the cytosol found outside the nucleus.
• It appears as a dense, roughly spherical or irregular
organelle.
5. ….CONTD
• The composition by dry weight of the nucleus is
approximately: DNA -9%,RNA-1%,Histone protein-
11%,residual protein-14%,acidic protein-65%
• In some types of white blood cells specifically
most granulocytes the nucleus is lobated and can be
present as a bi-lobed, tri-lobed or multi-lobed
organelle.
6. COMPONENTS OF NUCLEUS
1.NUCLEAR ENVELOPE:-
• The nuclear envelope also known as
nuclear membrane, consists of
two cellular membranes, an inner and
an outer membrane.
• The nuclear envelope is a highly
regulated membrane barrier that
separates the nucleus from the
cytoplasm in eukaryotic cells. It
contains a large number of different
proteins that have been implicated in
chromatin organization and gene
regulation.
7. (a) OUTER NUCLEAR MEMBRANE:-
• The nuclear membrane is a lipid bilayer.It consists of
two layers of lipid molecules.
• The outer layer of lipids has ribosomes, structures that
make proteins on its surface. It is connected to
the endoplasmic reticulum, a cell structure that
packages and transports proteins.
8. (b) INNER NUCLEAR MEMBRANE:-
• The inner membrane contains proteins that helps to organize the
nucleus and tether genetic material in place.
(c) NUCLEAR LAMINA:-
• The network of fibers and proteins attached to the inner
membrane is called the nuclear lamina. It structurally
supports the nucleus, plays a role in repairing DNA, and
regulates events in the cell cycle such as cell division and
the replication of DNA.
• The nuclear lamina is only found in animal cells, although
plant cells may have some similar proteins on the inner
membrane.
9. (d) PERINUCLEAR SPACE:-
• The perinuclear space is the
lumenal space between the
inner and outer nuclear
envelope bilayers that
separate the nucleus from the
cytoplasm.
• Because the outer nuclear
membrane is continuous with
the endoplasmic reticulum,
the perinuclear space is
continuous with the lumen of
the endoplasmic reticulum.
10. 2. NUCLEOPLASM:-
• The nucleoplasm is a highly viscous liquid contained within the
nucleus that surrounds the chromosomes and other subnuclear
organelles.
• A network of fibers known as the nuclear matrix can also be
found in the nucleoplasm.The nucleoplasm acts as a suspension
medium for components of the nucleus including
the nucleolus,and chromatin.
• Nucleotides required for DNA replication and enzymes involved
in other nuclear processes are also found dissolved within the
nucleoplasm.
11. 3. NUCLEOLUS:-
• The nucleolus is the nuclear
subdomain that assembles ribosomal
subunits in eukaryotic cell.
• The nucleolus, whose primary
function is to assemble ribosomes, is
the largest structure in the cell
nucleus
• The nucleolar organiser regions of
chromosomes, which contain the
genes for pre‐ribosomal ribonucleic
acid (rRNA), serve as the foundation
for nucleolar structure.
12. • The nucleolus disassembles at the beginning of mitosis,
its components disperse in various parts of the cell and
reassembly occurs during telophase and early G1 phase.
• Ribosome assembly begins with transcription of
pre‐rRNA. During transcription, ribosomal and
non‐ribosomal proteins attach to the rRNA.
• Subsequently, there is modification and cleavage of
pre‐rRNA and incorporation of more ribosomal proteins
and 5S rRNA into maturing pre‐ribosomal complexes.
• The nucleolus also contains proteins and RNAs that are
not related to ribosome assembly and a number of new
functions for the nucleolus have been identified. These
include assembly of signal recognition particles, sensing
cellular stress and transport of human immunodeficiency
virus 1 (HIV‐1) messenger RNA.
13. 4. CHROMATIN:-
• Chromatin is a mass of genetic material
composed of DNA and proteins that
condense to form chromosomes during
eukaryotic cell division. Chromatin is
located in the nucleus of our cells.
• The primary function of chromatin is to
compress the DNA into a compact unit
that will be less voluminous and can fit
within the nucleus.
• Chromatin consists of complexes of small
proteins known as histones and DNA.
14. Histones help to organize DNA into structures called
nucleosomes by providing a base on which the DNA can be
wrapped around.
A nucleosome consists of a DNA sequence of about 150
base pairs that is wrapped around a set of eight histones
called an octamer.
The nucleosome is further folded to produce a chromatin
fiber. Chromatin fibers are coiled and condensed to form
chromosomes.
……CONTD
15. Chromatin makes it possible for a number of cell
processes to occur including DNA
replication, transcription, DNA repair, genetic
recombination, and cell division.
The primary protein components of chromatin
are histones, which bind to DNA and function as
"anchors" around which the strands are wound.
……CONTD
16. CHROMATIN ORGANIZATION
In general, there are three levels of chromatin
organization:
1. DNA wraps around histone proteins,
forming nucleosomes and the so-called "beads on a
string" structure (euchromatin).
2. Multiple histones wrap into a 30-nanometer fibre
consisting of nucleosome arrays in their most
compact form (heterochromatin).
17. 3. Higher-level DNA supercoiling of the 30-nm fiber
produces the metaphase chromosome (during mitosis
and meiosis).
The overall structure of the chromatin network further
depends on the stage of the cell cycle.
During interphase, the chromatin is structurally loose to
allow access to RNA and DNA
polymerases that transcribe and replicate the DNA.
……CONTD
18. HETEROCHROMATIN
• Heterochromatin is very tightly
packed and condensed.
The formation of heterochromatin
involves modifications to histones
and the recruitment and
spreading of silencing complexes,
which cause changes to the
structure of chromatin.
• These changes affect various DNA
processes, including gene
transcription.
19. • Euchromatin consists of loosely wrapped chromatin, so the
DNA is more accessible.
• Modifications to the histone tails allow the chromatin to be
more open.
• Euchromatin is the part of the chromatin involved in the active
transcription of DNA into mRNA.
• As euchromatin is more open in order to allow the
recruitment of RNA polymerase complexes and gene regulatory
proteins, so transcription can be initiated.
EUCHROMATIN
20. • It controls the heredity characteristics of an organism.
• It is responsible for protein synthesis, cell division, growth and
differentiation.
• Stores heredity material in the form of deoxy-ribonucleic acid
(DNA) strands.Also stores proteins and ribonucleic acid (RNA)
in the nucleolus.
• It is a site for transcription process in which messenger RNA (m
RNA) are produced for protein synthesis.
FUNCTION OF NUCLEUS
21. REFERENCES:-
• CELL BIOLOGY BY CB.POWAR
• THE CELL BY GEOFFREY M.COOPER
• CELL & MOLECULAR BIOLOGY BY ROBERTIS
• https//www.ncbi.nlm.nih.gov
