The nucleus is a membrane-bound organelle that controls all cell activity. It contains the cell's genetic material in the form of DNA and is the site of DNA replication and transcription. The nucleus is enclosed by a nuclear envelope containing nuclear pores that regulate movement of molecules between the nucleus and cytoplasm. Chromatin in the nucleus packages DNA and participates in gene expression. The nucleolus forms within the nucleus and produces ribosomes.

1. THE CELL NUCLEUS
Tr. Apoorva

2. The Nucleus
The nucleus is the headquarters of the cell.
It is the most obvious organelle in any
eukaryotic cell and appears as a large dark
spot in EUKARYOTIC cells. It controls all
cell activity.

3.  The Nucleus is a membrane-enclosed
organelle which house most of the
genetic information and regulatory
machinery responsible for providing the
cell with its unique characteristics.

4.  THE NUCLEUS:
 FUNCTIONS
 It stores the cell's hereditary material, or DNA.
 Site of DNA replication
 Site of DNA transcription to mRNA
 Ribosomal formation
 Nucleolus: RNA & protein required for ribosomal
synthesis
 It coordinates the cell's activities, which include
growth, intermediary metabolism, protein
synthesis, and reproduction (cell division) by
regulating gene expression.

5.  THE NUCLEUS:
 STRUCTURE
 The contents of the nucleus are enclosed by a
complex nuclear envelope.
 Included within the nucleus are:
 1- Chromatin
 2- Nucleoplasm/ Nuclear matrix
 3- Nucleolus (concentrated area of chromatin,
RNA and proteins)

6. NUCLEUS

7. nuclear
envelope
nucleolus
nuclear
pores
chromatin

8. nucleus
nuclear
pores

9.  The NUCLEAR ENVELOPE (NE)
The nuclear envelope completely encloses the
nucleus and separates the cell's genetic
material from the surrounding cytoplasm,
serving as a barrier to prevent
macromolecules from diffusing freely between
the nucleoplasm and the cytoplasm.

10.  The NE consists of two cellular membrane, an
inner and an outer membrane, arranged parallel
to one another and separated by 10 to 50
nanometers (nm).
 The outer nuclear membrane is continuous with
the membrane of the rough endoplasmic
reticulum (RER), and is similarly studded with
ribosomes.
 The space between the membranes is called the
perinuclear space and is continuous with the RER
lumen.

12.  The inner surface of the NE is bound to a thin
filamentous network (lamins polypeptides)
called the nuclear lamina. It provides
mechanical support to the NE and seeves as
sites for attachment for chromatin fibers.
 Mutations in the lamin genes are responsible
for several distinct human diseases (e.g. a rare
form of muscular dystrophy).

13.  THE NUCLEAR PORE
 The nuclear pores are the gateways across
which movement of RNAs and proteins takes
place between the nucleus and cytoplasm in
both direction.
 Proteins synthesized in the cytoplasm cross
the nuclear envelop to initiate replication and
transcription of genetic material. Similarly,
mRNA,tRNA and ribosomal subunits built in
the nucleus cross through the nuclear pores to
the cytoplasm.

14.  The pore is 100 nm in total diameter and
consists of around 100 proteins which allows
the free passage of small water-soluble
molecules while preventing larger molecules,
such as DNA and proteins.
 The nucleus of a typical mammalian cell has
about 3000 to 4000 pores throughout its
envelope.

15. CHROMATIN
The interphase chromosomes is present in a highly
extended nucleoprotein fibers called chromatin.
 Chromatin is the complex of DNA,RNA and
protein (Histones and Non-Histomes) that makes
up chromosomes.
 Each unreplicated chromosome contains a single
continuous DNA molecule.
 The mitotic chromosome represents a highy
condensed structure (10000:1)

16. chromatin
chromosome

18. Replicated
chromosome
P arm
kinetochore
centromere
Q arm
sister chromatids

19.  Each human somatic cell contains 23 pairs
of different chromosomes ( DIPLOID
CELLS) .
 GAMETES (sperm and egg cells) have one set
of 23 chromosomes ( HAPLOID CELLS).
 One member of each pair is derived from the
individual's father, and the other member is
derived from the mother. One of the
chromosome pairs consists of the sex
chromosomes.

20.  In normal males, the sex chromosomes are a Y
chromosome inherited from the father and an
X chromosome inherited from the mother.
 Two X chromosomes are found in normal
females, one inherited from each parent.
 The other 22 pairs of chromosomes are termed
autosomes. The members of each pair of
autosomes are said to be homologs, or
homologous, because their DNA is very
similar. The X and Y chromosomes are not
homologs of one another.

21.  Human Chromosomes
 Chromosomes are the physical carriers
of genetic information.
 The packaging of DNA into
chromosomes involves several orders
of DNA coiling and folding.

22.  LEVELS OF CHROMATIN ORGANIZATION
 The structure of chromatin varies considerably as
the cell progresses through the cell cycle. The
changes in structure are required to allow the
DNA to be used and managed.

23. Chromatin Function
 Package DNA into a smaller volume to fit in
the cell.
 Strengthen the DNA to allow mitosis and
meiosis
 Serve as a mechanism to control
expression.

26. Simplified diagram of proposed solenoid
model of DNA coiling which leads to the
visible structure of the chromosome.

27. NUCLEOPLASM
 The nucleoplasm is a highly viscous liquid
that surrounds the chromosomes and
nucleoli. Many substances such as
nucleotides (necessary for purposes such as
the replication of DNA) and enzymes (which
direct activities that take place in the nucleus)
are dissolved in the nucleoplasm.

28.  Nucleolus
:
 The prominent structure in the nucleus
is the nucleolus.
 The nucleolus produces ribosomes,
which move out of the nucleus and
take positions on the rough
endoplasmic reticulum where they are
critical in protein synthesis.