Eukaryotic nucleus structure Boby

1. Nucleus
Dr Boby T Edwin
TKMCAS, Kollam
bobytedwin2003@gmail.com
BB/TKMBOT/Cytology/5

3.  The nucleus was discovered by Robert Brown in 1831.
 The nucleus is considered to be the core of the cell.
 It commands all metabolic events.
 Miescher (1869) discovered nucleoproteins and nucleic
acids and suggested that it is an important component of the
nucleus.
 In 1888, Waldeyer observed and designated chromosomes.
 The number of nuclei per cell may vary from one to many.
 Generally, cells contain a single nucleus, and such cells are
called uninucleate cells.
 Paramaecium protozoan contains 2 nuclei and is called as
Binucleate.
 Some cells possess 3 or more nuclei and are called as
Polynucleate.
Nucleus

4.  The nucleus may be elliptical or discoid in
shape
 Nucleus is covered with a nuclear envelope
which contains nuclear pores involved in
transport of molecules across the nuclear
membrane.
 Nucleus contains nuclear membrane,
nucleoplasm. chromatin reticulum and
nucleolus
 The nucleolus observed
during interphase are
called interphase nucleus.

5. Ultra structure of Nucleus
Nuclear Membrane
 . Interphase nucleus is
surrounded by an envelope
called nuclear membrane
(karyotheca) containing two
layers outer nuclear
membrane (ectokaryotheca)
and inner (endokaryotheca)
nuclear membrane.
 Between these two layers a
space is present called
perinuclear space (150 to
300 angstrom).
 The perinuclear space is filled

6. Ultra structure of Nucleus
Nuclear Membrane
 The nuclear membranes are unit
membranes and
lipoproteinaceous.
 The inner nuclear membrane is
lined by a fibrous material called
nuclear lamina composed of a
protein called laminin (A and B).
 The outer nuclear membrane
also contains lamina but not
organized.
 The outer nuclear membrane is
bounded with ribosomes.
 The outer nuclear membrane
has connections between
endoplasmic reticulum,
golgibodies and plasma

7. Ultra structure of Nucleus
• Inner to nucleus a
matrix is present. It
is called
nucleoplasm.
• The nuclear
membrane contains
many pores called
nuclear pores
which form
passage ways
between
nucleoplasm and
cytoplasm.

8.  The nuclear membrane contains many
pores.
 Each pore has a diameter of 200 to
400 Angstrom.
 The nuclear pore has a complex
organization referred as nuclear pore
complex.
 At the rim of the pores, the inner and
outer nuclear membranes are
continuous.
 A cylindrical structure called annulus
lies inside the pores. The annulus
slightly extends to cytoplasm and
nucleoplasm.
 The nuclear membrane and the
annulus together forms pore complex.
 The centre of the pore contains a
passage called central channel. The

9. complex
 The two irises are placed one above
the other. Each iris is formed of 8
arms. The iris opens sequentially
like diaphragm of a camera.
 On the cytoplasmic side the nuclear
pore is provided with and
ocatagonal ring called cytoplasmic
ring connected to the transporter
by 8 spokes.
 On the nuclear side, the nuclear
pore is provided with another
octagonal ring called
nucleoplasmic ring connected to
the transporter by 8 spokes.
 On the nucleoplasm side, the
nuclear pore is provided with a
basket.
 The basket consists of a small ring,
8 filaments connecting the small
ring and the nucleoplasmic ring.
 The pore complex helps the
Functions of nuclear
membrane or nuclear
envelope are regulation of
nucleo-cytoplasmic
exchange, formation of
Endoplasmic reticulum and

10.  Nucleoplasm
 Nucleoplasm is otherwise called nuclear sap or
karyolymph.
 Nucleoplasm contains a number of proteins, such as RNA
polymerase, DNA polymerase, several types of cytochromes
and histones; all are synthesised in cytoplasm of the cell
and transported into the nucleus.
 Dense jelly like mass in nucleus is called karyolymph and
the fibrous materials are called chromatic reticulum.
 The proteins present in nuclear sap are acidic and basic.
 The basic proteins include nucleoprotamines and
nucleohistons. The protamines are bound to DNA through
salt linkages and histones through ionic bonds.
 The nucleoplasm contains numerous ribonucleoprotein
granules or particles (RNP).
 They are mRNA precursors.

11. Chromatin Reticulum
 Lightly stained thread like bodies present in nucleoplasm
are called chromonemata.
 The network or assemblage of chromonemata is called
the chromatin reticulum.
 During prophase these
chromatin reticulum
condenses to become chromosomes. (chromo-coloured).
 The permanently condensed chromosomes are called
heteropycnotic chromosomes while other are called
euchromosomes.

12. Source of image : https://www.nature.com/articles/nchembio0206-64
Wikipedia

13.  The chromatin reticulum during interphase
contains higly stained condensed heteropycnotic
regions called heterochromatin and less
stained, non-condensed, nonheteropycnotic
regions called euchromatins.
 The heterochromatins are genetically and
metabolically inert. While the euchromatins are
active in metabolism and genetics.

14.  During some stages of cell division, the
chromatin contains beaded appearance
with granular regions called
chromomeres.
 Chromomeres are superimposed local
coils of chromatin reticulum
 In some nuclei, one or more dense
regions can be observed in chromatin
reticulum they are called
chromocentres.
 Chromocentres are the regions where
heterochromatic regions merge
together. Heterochromatic can either
constitutive or facultative.
 Constitutive heterochromatin is
always condensed while the facultative
heterochromatin undergoes
condensation only at some stages of life
cycle.
 Chemically chromatin reticulum is deoxy
ribonucleoprotein formed of DNA and
basic protein histone.

15. Nucleolus
 The nucleus contains one or more dense bodies called
nucleoli. They are discoved by Fontana in 1874. They are
distinct in interphase nucleus. They disorganize and
disappear during the late prophase stage of cell division. The
formation of nucleolus is associated with a specific
chromosomal locus called nucleolar organizer region.
Nucleolus lacks a limiting membrane. A nucleolus has four
parts
 Nucleolar matrix: Matrix is the amorphous enzyme rich
proteinaceous ground substance with high concentration of
RNA and protein.
 Granular zone (pars granulosa): this region is the periphery

16.  Fibrillar zone ( par fibrosa): this
zone is formed of fibres. The
fibrils are 50 to 80 angstrom long.
 The fibrils are called
nucleolonema formed of
ribonucleoprotein filaments which
are the precursors of ribosomes.
 Nucleolar chromatin (nucleolus
associated chromatin): Nucleolar
chromatin are chromatin
associated with nucleolus. They
are of two types perinuclear
chromatin which surrounds the
nucleolus through periphery and
intra- nucleolar chromatin which
forms septa like projection from
perinuclear chromatin to the
nucleolar matrix.
 Some chromosomes have the
presence of low electron density
region and this region is called

17. Functions of Nucleus
 Synthesis, storage and processing of RNA
 Storage of ribosomal proteins and assembly of
ribosomes

18. Thank you