The nucleus is a membrane-bound organelle found in eukaryotic cells that contains the cell's genetic material. It maintains the integrity of genes and controls cell activities through regulating gene expression. The nucleus is surrounded by a double membrane with nuclear pores that allow transport between the nucleus and cytoplasm. Chromatin fibers containing DNA and histones are organized into chromosomes inside the nucleus. The nucleolus is a dense structure where ribosomal RNA is synthesized.

1. Nucleus
H E T V I K A N O J I A
A S S I S T A N T P R O F E S S O R
F A C U L T Y O F S C I E N C E
N O B L E U N I V E R S I T Y

3. Nucleus
Nucleus” is a Latin word meaning Kernel. It is the “CONTROL CENTER” of the cell.
It was First cell organelle to be discovered It is membrane bound organelle found in eukaryotic
cells.
Main functions are - to maintain the integrity of genes - to control the activities of the cell by
regulating gene expression

4. Nucleus
The nucleus, the largest organelle in animal cells, is surrounded by two membranes, each one a
phospholipid bilayer containing many different types of proteins
The inner nuclear membrane defines the nucleus itself.
In most cells, the outer nuclear membrane is continuous with the endoplasmic reticulum, and
the space between the inner and outer nuclear membranes is continuous with the lumen of the
endoplasmic reticulum.

5. Nucleus
The two nuclear membranes appear to fuse at nuclear pore complexes, ringlike structures
composed of specific membrane proteins through which material moves between the nucleus
and the cytosol
Intermediate-filament proteins called lamins form a two-dimensional network, called the
nuclear lamina, along the inner surface of the inner membrane, giving it shape and rigidity. The
breakdown of the lamina occurs early in cell division.

6. Nucleus
In a growing or differentiating cell, the nucleus is metabolically active, as it is the site of DNA
replication and the synthesis of ribosomal RNA, mRNA, and a large variety of noncoding RNAs.
Inside the nucleus one can often see a dense subcompartment, termed the nucleolus, where
ribosomal RNA is synthesized and ribosomes
The total DNA in an organism is referred to as its genome.

7. Nucleus
In most prokaryotic cells, most or all of the genetic information resides in a single circular DNA
molecule about a millimeter in length; this molecule lies, folded back on itself many times, in the
central region of the micrometer sized cell.
In contrast, DNA in the nuclei of eukaryotic cells is distributed among multiple long linear
structures called chromosomes.
The length and number of chromosomes are the same in all cells of a particular species, but vary
among different species

8. Nucleus
Each chromosome comprises a single DNA molecule associated with numerous histones and
other proteins.
In a nucleus that is not dividing, the chromosomes are dispersed and are not dense enough to
be observed in the light microscope. Only during cell division are individual chromosomes visible
by light microscopy.
When nondividing cells are visualized in an electron microscope, the non-nucleolar regions of
the nucleus, called the nucleoplasm, can be seen to have dark- and light-staining areas.
The dark areas, which are often closely associated with the nuclear membrane, contain
condensed, concentrated DNA that cannot be transcribed into RNA, called heterochromatin.

9. 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.

10. STRUCTURE
Average diameter of nucleus is 6um, which occupies around 10% of cell volume
The contents of the nucleus are enclosed by a complex nuclear envelope.
Included within the nucleus are:
1- Chromatin
2- Nucleoplasm
3- Nucleolus (concentrated area of chromatin, RNA and proteins)

11. The NUCLEAR ENVELOPE
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.
Also known as perinuclear envelope, nuclear membrane or karyotheca Encloses the nucleus and
separates the cell's genetic material from the surrounding cytoplasm.
The space between the membranes is called the perinuclear space and is continuous with the
RER lumen.

13. NUCLEAR PORE COMPLEX
It is a complex in the nuclear membrane that enables the trafficking of molecules between the
nucleus and cytoplasm

16. Nuclear envelope and lamina

17. Lamins are filamentous proteins in the
intermediate filament family
Lamin phosphorylation in prophase
disassembles the nuclear lamina &
allows for nuc. envel. breakdown

18. CHROMATIN
The interphase chromosomes is present in a highly extended nucleoprotein fibers called
chromatin.
Chromatin is the complex of DNA and protein (Histones) that makes up chromosomes.
Each unreplicated chromosome contains a single continuous DNA molecule.
The mitotic chromosome represents a highly condensed structure

19. Heterochromatin
= too compacted,
transcriptionally
inactive
Euchromatin = can
be transcriptionally
active

20. Nucleolus
Nucleolus is the discrete densely stained structure found in nucleus It is a nuclear inclusion that
is not surrounded by a membrane Present in cells that are actively synthesizing proteins Its size
depends on metabolic activity of cell Average size .5-5um in dia Nucleolus .
It is mainly associated with synthesis of rRNA

21. Nucleoplasm
Nucleoplasm is the protoplasm within the nuclear envelope It consists of a nuclear matrix and
various types of particles Highly viscous liquid which scaffolds chromosomes, nucleolus and
various granules like heterochromatin, perichromatin granules Many substances like nucleotides
and certain enzymes are also dissolved in it Nucleoplasm