HeLa cells stained for nuclear DNA with the blue fluorescent Hoechst dye. The central and rightmost cell are in interphase, thus their entire nuclei are labeled. On the left, a cell is going through mitosis and its DNA has condensed. Cell biology The animal cell Animal Cell.svg Components of a typical animal cell: Nucleolus Nucleus Ribosome (little dots) Vesicle Rough endoplasmic reticulum Golgi apparatus (or "Golgi body") Cytoskeleton Smooth endoplasmic reticulum Mitochondrion Vacuole Cytosol (fluid that contains organelles, comprising the cytoplasm) Lysosome Centrosome Cell membrane In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, meaning kernel or seed) is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many.

1. VEENA P KUMAR
1st YEAR MSC.MICROBIOLOGY
SCHOOL OF BIOSCIENCE
Veena P Kumar 1

2.  Eukaryotic membrane based organelle.
 Comprises of linear DNA molecules.
 Monitors cellular activity by gene regulation.
 Enclosed in a double membrane envelope.
 Comprises of pores to allow transport of
molecules.
 Largest cell organelle in animals.
 Comprises of viscous fluid throughout the
organelle(nucleoplasm).
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3.  Discovered by A. V. Leeuwenhoek for first
time.
 Franz Bauer in 1802 also described it.
 Scottish botanist Robert Brown explained it in
more detail.
 Later it was concluded that it is a membrane
bounded organelle found in eukaryotic cells.
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5. 1. Nuclear envelope - pore riddle.
2. Nucleoplasm – fluid interior portion.
3. Nucleolus – dense cluster of RNA.
4. Chromatin – all DNA + protein.
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6.  Existence of nuclear membrane – late 19th
century.
 Phase contrast microscopy – 20th century.
 Further investigations – double membrane
with space between 2 phospholipid bi layers.
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7.  Inner and outer nuclear membrane with
perinuclear space.
 7-8nm thick and trimellar appearance.
 Inner membrane lined with fiber net work-
nuclear lamina-10 - 40nm.
 Nuclear lamina- intermediate filament
(protein) called as Lamins.
 Nuclear lamina support to NE & attachment
site for chromatin.
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8.  Outer membrane continuous with ER.
 Outer membrane studded with ribosomes-
protein synthesis.
 Perinuclear space-20 to 40nm continuous
with cisternae of ER.
 Filaments of cytoskeleton extend outward
cytoplasm-anchored to organelles/plasma
membrane- known as nuclear matrix.
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10.  Most distinctive feature of nuclear envelope.
 Small cylindrical channels- direct contact b/w
cytosol & nucleoplasm.
 Readily visible- freeze fracture microscopy.
 Density- cell type & activity.
 Mammalian nucleus-3000to4000 pores.
 Density 10-20 pores/sq. micrometer.
 Structural complexity control transport of key
molecules.
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12.  Nuclear pores are large protein complexes
that cross the nuclear envelope, which is the
double membrane surrounding the eukaryotic
cell nucleus.
 Diameter 120 nm, over all mass 120 million
da, 100 or more different poly peptide sub
units.
 Shape- wheel lying on its side within NE.
 Two parallel rings –rim of wheel – 8 sub units.
 Anchor protein - proteins extend from rim
into peri nuclear space.
 Fibers extend from rings to cytosol and
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15.  Enzymes and proteins-replication and
transcription must be imported from
cytoplasm.
 RNA and ribosomes for protein synthesis in
cytoplasm must be obtained rom nucleus.
 Natures solution – evolution of eukaryotic Ne
with pores.
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17.  3000 t0 4000 nuclear pores are usually
present in actively growing mammalian cell.
 Ribosomes are partially assembled in nucleus.
 In an actively growing mammalian cell-
2000ribosomal unit per minute.
 Transport rate of ribosomal subunit- 5 to 6
units/minutes/pore.
 During replication histones needed
@3,00,000 molecules/min.
 Rate of inward movement-100 histones/min.
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18.  Apart from macromolecules pore allow –small
molecules and ions.
 Aqueous channels-direct contact cytosol and
nucleoplasm.
 Permeable to small molecules and ions
 Nucleoside triphosphates required for
DNA&RNA synthesis-diffuse freely through
pores.
 Small molecules- metabolic pathways.
 Eight 9nm channels between the spokes +
9nm channel at center of transporter.
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20.  Eukaryotic chromosomes 2 two broad
components.
1.Nucleic acid;
 DNA
 + small amount of RNA
2.Proteins;
 Histones-core histones , linker histones.
 Non histone proteins.
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21.  Histones bind to-vely charged DNA –stability
to the DNA.
 E/M examination of inter phase chromatin –
ellipsoidal beads joined together by linker
DNA known as nucleosomes
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22.  Simplest packing
structure of DNA .
 146bp DNA wrapped
around histone octamer.
 Octamer-2copies of four
histones.
 DNA length varies
between species.
 Core DNA –DNA
associated with histone
octamer.
 Linker DNA –DNA b/w
histone octamer- 8-114
bp
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24. • Chromatin can be
differentiated into two
regions .
• Euchromatin -
• slightly stained.
• Hetero chromatin-
• densely stained
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25.  Heterochromatin appears as small, darkly
staining, irregular particles scattered
throughout the nucleus or accumulated
adjacent to the nuclear envelope.
 Euchromatin is dispersed and not readily
stainable.
 Euchromatin is prevalent in cells that are
active in the transcription of many of their
genes while heterochromatin is most
abundant in cells that are less active or not
active.
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26.  DNA, or deoxyribonucleic acid, contains the
information needed for the creation of
proteins (which include enzymes and
hormones) and is stored in the nucleus.
 The nucleus is the site of DNA duplication,
which is needed for cell division (mitosis) and
organism reproduction and growth.
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27.  Polymeric molecules made of 4 different
monomeric units called nucleotides.
 Nucleotide :
1. A pentose(5 carbon)sugar.
2. A nitrogen base
3. A phosphate group
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28.  For DNA pentose sugar is ribose.
 Nitrogenous bases ; 2 classes
1. Purines – adenine(A)&guanine(G)
2. Pyrimidines –
Thymine(T)&Cytosine(C)
 IN RNA thymine is replaced by uracil
 Nucleoside =base + sugars.
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30.  In 1953 James.D.Watson and Francis.H.C. Crick
published paper –model for physical and
chemical structure of DNA molecule.
 Its was based on earlier findings by different
scientists.
1. Erwin charqoff
1. Rosalind Franklin & Maurice H F Wilkins
 Watson & crick considered all evidence & began
to build three dimentional model of structure of
DNA
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32.  Estable and Sotelo (1951) described the
structure of a nucleolus under the light
microscope.
 According to them, nucleolus consists of a
continuous coiled filament called the
nucleolonema embedded in a homogenous
matrix.
 The first description of nucleolar ultra
structure was given by Borysko and Bang
(1951) and Bernhard (1952).
 They described two main nucleolar
components, a filamentous one
corresponding to the nucleolonema and a
homogenous one corresponding to the pars
amorpha (matrix).
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34.  The nucleolus is a non-membrane bound
structure composed of proteins and nucleic
acids found within the nucleus.
 The ribosomal RNA is transcribed in the
nucleolus.
 There are three main parts that are
recognized: the fibrillar centers, the dense
fibrillar component, and the granular
components.
 The nucleolus is the main part of the cell
that produces the ribosomes that make the
proteins.
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35. FC ; Fibrillar centres
DFC; Dense fibrillar
centres
GC; Granular centres
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36.  As the nucleus is the "brain" of the cell, the
nucleolus could loosely be thought of as the
brain of the nucleus.
 The nucleolus takes up around 25% of the
volume of the nucleus.
 This structure is made up of proteins and
ribonucleic acids (RNA).
 Its main function is to rewrite ribosomal RNA
(rRNA) and combine it with proteins. This
results in the formation of incomplete
ribosomes.
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37.  There is an uninterrupted chain between
the nucleoplasm and the interior parts of
the nucleolus, which occurs through a
system of nucleolar passages.
 These passages allow macromolecules with
a molecular weight up to 2,000 kDa to be
easily circulated throughout the nucleolus.
 Because of its close relationship to the
chromosomal matter of the cell and its
important role in producing ribosomes, the
nucleolus is thought to be the cause of a
variety of different human diseases.
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38. SYNTHESIS OF RIBOSOME IN NUCLEOLUS
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39.  Mutations in lamin genes leads to
Laminopathies.
 Eg: Progeria
Progeria leads to premature aging.
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40.  IQGAP1 protein helps in amplification of
cancer cells.
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41.  Dicer is a protein forms RISC( RNA Induced
silencing complex) and plays a vital role in
RNAi.
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