Presentation include Nucleus and its components like nuclear envelope, nucleolus, chromatin fibers, ultra structure of nucleus and its general functions.

1. Nucleus
&
Its Components
- Akshay More,
M.Sc. Biotechnology-1.,
Modern College, Ganeshkhind,
Pune.

2. Contents
• History
• Occurrence and position
• Morphology
• Ultrastructure:
1. Nuclear Envelope
2. Nucleoplasm
3. Chromatin Fibres
4. Nucleolus
• Functions

3. History:
• First discovered & named by Robert Brown
(1833).
• Term Nucleolus -Bowman(1840).
• Term Chromatin – W. Flemming(1879).
• Term Cytoplasm & Nucleoplasm- Strasburger
(1882)

4. Occurrence an Position
• Occurrence:
1. Found in all eukaryotic cells of plants & animals.
2. Exceptions: Mature sieve tube & erythrocytes.
3. Prokaryotes(Bacteria) lack true nucleus.
• Position:
Usually at Centre but change time to time acc. to metabolic state.
• Staining Properties:
Fluorescent dyes with aromatic amino or guanidine groups,
such as propidium iodide (PI), ethidium bromide (EB),
diaminophenylindole (DAPI), acridine orange (AO), and Hoechst
dyes, interact with nucleotides to emit fluorescence.

5. Morphology
• Number:
1. Mononucleate cells.
2. Binucleate cells. e.g. Paramecium, hepatocytes, chondrocytes.
3. Polynucleate cells: (3-100)
I. Animals- Syncytial cells (Osteoblasts, striated muscle fibres).
II. Plants- Coenocytes (Algae-Vaucheria, Fungi).
• Shape:
1. w.r.t. shape of cell.
2. Shapes: Spheroid, Cuboid, Isodiametric, ellipsoid.
3. e.g. Squamous epithelium- discoidal shape, Leukocytes- irregular.

6. • Size:
- Generally occupies 10% of cell volume.
- Size varies from 3μm to 25 μm depending on cell type.
- Size of nucleus is directly proportional to cytoplasm.
- R. Hertwig gives formula for determination of size,
Vn
NP= Vc- Vn where,
NP- Nucleoplasmic ratio, Vc- Volume of cell, Vn- Vol. of nucleus.
-Size is related with ploidy level.
e.g. Haploid cells have small-sized nucleus than diploid and polyploid
cells and vice versa.
- Thus size depends on Cell Volume, Amount of DNA and protein,
Metabolic phase of cell.

7. Structure of nucleus Electron Micrograph of
nucleus

8. Ultrastructure
1. Nuclear envelope:
• Encloses DNA
• Formed from-
1. Spherical inner nuclear membrane (5-10 nm thick).
-Contains sp. Proteins act as binding site for IFs- nuclear lamina.
2. Outer Nuclear membrane.
- Continues with ER, studded with ribosomes- proteins.
• Perinuclear space: 10-50 nm diam.
-contain fibres, lipid droplets, crystalline deposits.
A) Nuclear lamina-
-Protein meshwork, 50-80 nm thick.
- Lines inside surface of inner nuclear membrane.
-Plays crucial role in assembly of interphase nuclei.

9. Nuclear envelope

10. B) Nuclear Pores:
1) Structure:
-Circular, Diameter 10nm to 100nm.
-Nuclear pore complex (M.W.= 50-100 million daltons) have octagonal
symmetry, contain two rings (R), large particle that forms central plug
and radial spokes.
- Proteins=
i) Integral membrane protein, a glycoprotein of 120 K daltons.
ii) Transporter Protein, 63 k daltons.
2) Pore Density:
- Correlated with transcriptional activity of cell.
- R.B.Cs and lymphocytes~ 3 pores/μm^2.
- Proliferating cells (liver)~ 15-20 pores/μm^2

11. Nuclear pore complex

12. 3) Transport through Nuclear Pores:
- If cell is synthesizing DNA, it needs to import about 10^6 histone
molecules from cytoplasm every 3 mins., for packaging DNA.
- mRNA complexed with special proteins forming ribonucleoprotein
particles are actively export through nucleus.
[movement of granular material (presumed to be a ribosomal subunit)
through a nuclear pore]

13. Transport
of
Proteins
through
nuclear
pore complex

14. 2. Nucleoplasm:
- Transparent, semi-solid, granular, slightly acidophilic,
- Also called nuclear sap, nucleoplasm, karyolymph.
- Composed of=
1. Nucleic Acids:
Deoxyribose Nucleic Acid, Ribose Nucleic Acid.
2. Proteins :
Complex proteins, categorized into-
I. Basic Proteins:
-Takes basic stains, so the name.
e.g. A) Nucleoprotamines- M.W. = 4K D, usually bound with DNA.
B) Nucleohistones- M.W.= 10 to 18 K D.
II. Non-Histones/ Acidic Proteins:
e.g. Phosphoproteins.

15. 3) Enzymes :
- Contains enzymes necessary for DNA, RNA synthesis.
- e.g. Polymerases, NAD Synthetases, Adinosine deaminases, guanase,
aldolase etc.
- Also contains cofactors and coenzymes like ATP and Acetyl CoA.
4) Lipids :
Small Lipid content ( Stoneburg, 1937 and Dounce , 1955).
5) Minerals:
Contain several inorganic compounds such as-
P, K, Na, Ca, Mg etc.

16. 3. Chromatin Fibres:
- Thread like, coiled and much elongated structures.
- Takes basic stains like basic fuschin.
- Observed only during interphase.
- Chemically made of DNA and proteins, Protein: DNA= 1:1.
- Types=
A) Heterochromatin:
-Darkly stained, condensed region.
- Supposed to be metabolically & genetically inactive.
- Because it contains small amount of DNA & Large amount of RNA.
B) Euchromatin:
-Lightly stained, diffused region.
-Genetically active.
-Large amount of DNA present.

17. Spaghetti Model for Organization of Chromatin
in the Interphase Cell Nucleus

18. 4. Nucleolus:
• Prominent spherical colloidal acidophilic body.
• Bacteria and Yeasts lack nucleolus.
• Size depends on synthetic activity of cell.
- So, sperm cells, blastomeres have smaller nucleolus than oocytes,
neurons, secretory cells.
• Number: One , two or four, depending on no. of chromosomes.
• Position: Eccentric.
• Associated with Nucleolar Organizer (NO) represents 2° constriction
of NO chromosomes.
A) Chemical Composition:
- Not bounded by any limiting membrane.
- Contains NO DNA, 4 types of rRNAs, 70 types of ribosomal proteins,
RNA Binding Proteins ( e.g. nucleolin) and RNA splicing
nucleoproteins (U1, U2…, U12).

20. - Contains Phospholipids, orthophosphates, Calcium ions,
- Also contains enzymes like acid phosphatases, nucleoside
phosphorylase, RNA Methylases.
B) Ultrastructure and Function:
- They are sites for biogenesis of ribosomal subunits (40S & 60S).
- Here three types of rRNAs are transcribed (18, 5.8, 28S) from
precursor 45S transcript which undergoes processing with the help of
proteins=
I. Nucleolin
II. U3 sn RNA.
- All the components of ribosome are synthesized and assembled into
two types of ribosomal subunits and are transported back to
cytoplasm.
- Different stages of formation of ribosomes( Initiation, production,
maturation) are completed in three distinct regions of nucleolus.

22. a) Fibrillar centre:
- Represents innermost region of nucleolus.
- RNA genes of NO of chromosomes are located here.
- Transcription of these genes initiated here.
b) Dense fibrillar component:
- This region surrounds fibrillar centre.
- RNA synthesis proceeds where 70 ribosomal proteins binds to transcript in
this region.
c) Cortical granular components:
- Outermost region.
- Processing and maturation of pre-ribosomal particles.
C) Mitotic cycle of nucleolus :
- Appearance changes during cell cycle.
- During mitosis and meiosis, nucleolus disappears during prophase.
- As cell approaches mitosis, RNA synthesis stops, nucleolus first decrease
in size and then disappears as chromosomes condenses.
- In telophase, RNA synthesis restarts, where, tiny nucleoli reappear at the
chromosomal locations.

23. • General functions of Nucleus :
1) Functions of nucleolar genes are to produce the ribosomal RNA
molecules which forms ribosomes.
2) Has a vital role in Protein synthesis (ribosomal proteins).
3) Nucleolus of nucleus plays vital role in cell division. If nucleolus get
injured, cell division stops.
4) Chromatin plays an important role in the inheritance of characters
from one generation to another,
5) Nuclear sap is the site of enzyme activity. It is supposed to participate
in formation of spindles during cell division.
6) The nuclear pores regulate exchange of materials between nucleus
and cytoplasm.