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Presentation Transcript

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Introduction : 

“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 Introduction 3 Nucleus

Historical Perspective : 

Microscopist Antonie van Leeuwenhoek (1632 - 1723) observed a "Lumen", the nucleus, in the red blood cells of salmon Mentioned by Franz Bauer in 1804 Scottish botanist Robert Brown elaborately described the nucleus studying orchids in 1831 In 1838 Matthias Schleiden proposed that the nucleus plays role in generating cells and introduced the name "Cytoblast" (cell builder) Historical Perspective 4 Nucleus

Structure : 

Average diameter of nucleus is 6um, which occupies around 10% of cell volume Nuclear Envelope Nuclear Pores and complex Nuclear lamina Chromosomes & Chromatin Nucleolus Nucleoplasm Subnuclear bodies Structure 5 Nucleus

Nuclear envelope : 

Also known as perinuclear envelope, nuclear membrane or karyotheca Encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm It is a lipid bilayer Consists two cellular membranes, an inner & outer membrane, arranged parallel to one another and separated by 10-50(nm) of space Nuclear envelope 6 Nucleus

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7 Nucleus

0uter Membrane : 

0uter Membrane 6 nm thick Faces cytoplasm and is continuous at certain sites with the RER A loosely arranged mesh of intermediate filaments (vimentin) Ribosomes stud the cytoplasmic surface of the outer nuclear membrane Ribosomes synthesize proteins that enter the perinuclear cisterna (space between two membranes 20-40nm wide) 8 Nucleus

Inner membrane : 

Faces the nuclear material Primary site for location of inner nuclear membrane proteins IMP Inner membrane proteins – LAP2, SUN1, EMERIN, MAN1, LBR (used during formation of NE during mitosis as well as some role in transcriptional activity) Outer and inner membranes are fused at the nuclear pore complex sites Inner Membrane is supported underneath by Nuclear lamina Inner membrane 9 Nucleus

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10 Nucleus

Nuclear lamina : 

Network of intermediate filaments ,Composed primarily of lamins A, B1, B2 and C Helps in organizing the nuclear envelope and perinuclear chromatin ,Also plays a role in DNA elongation phase Essential during mitotic events where, Phosphorylation of lamins leads to disassembly, and dephosphorylation results in reassembly of the nuclear envelope Apoptosis a highly regulated process in which nuclear lamina is disassembled following proteolytic activity of capase protein Nuclear lamina 11 Nucleus

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12 Nucleus

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LAMINOPATHIES Defects in the genes coding for nuclear lamina causes laminopathies Hutchinson-Gilford Progeria – premature aging Emery-Dreifuss muscular dystrophy – muscle wasting Restrictive dermopathy – a disease associated with extremely tight skin and severe neonatal abnormalities Pelger-huet anomaly- blood laminopathy associated with LBR GENE defect (hposegmented nucleus of neutrophils) 13 Nucleus

Nuclear pores and complex : 

Nuclear pores are aqueous channels through the nuclear envelope Composed of multiple proteins called nucleoporins” Have molecular weight of 125 million daltons Nucleus of a cell has 3000 - 4000 pores Pores are formed by fusion of outer and inner nuclear membranes NPC permits passive movement across the nuclear envelope via 9-11nm channels by simple diffusion Nuclear pores and complex 14 Nucleus

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Nucleus 15 Allows free passage of water soluble molecules Most proteins, ribosomal subunits and RNA are transported via transport factors called KARYOPHERINS a) Importins –that mediate movement into the nucleus b) Exportins –that mediate movement out of nucleus NPC is composed of nearly 100 proteins, arranged in eight-fold symmetry around the margin of the pore.

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NUCLEAR PORE STRUCTURE Cytoplasmic ring Nucleoplasmic ring Middle ring. Nucleoplasmic side- Nuclear basket Cytoplasmic side - displays fibers extending into cytosol 16 Nucleus

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17 Nucleus

Chromosomes : 

It is an organized structure of DNA Containing genetic information of cell, regulatory elements and other nucleotide sequences Chromatin is a complex of DNA and histone protein, which packages chromosomes also known as nucleosomes The structure of chromosomes and chromatin varies throughout the cell cycle Interphase chromatin consists of euchromatin and heterochromatin (chromosomes are not visible during this phase) Chromosomes 18 Nucleus

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Euchromatin – contains active form of DNA Heterochromatin - contains inactive form Metaphase chromatin- the chromatin becomes more and more condensed and compact, making the chromosome visible with a classic four arm structure, having a pair of sister chromatids attached at centromere Humans have 23 pairs of chromosomes- 22 are autosomes & 2 sex chromosomes 19 Nucleus

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20 Nucleus

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Anti Nuclear Antibodies (ANA) Antibodies to certain chromatin organizations, particularly nucleosomes, have been associated with a number of AUTOIMMUNE DISEASEAS such as sytemic lupus erythematosus systemic sclerosis/ scleroderma 21 Nucleus

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 22 Nucleus

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It is generally detectable when the cell is in interphase Synthesis of rRNA and its assembly into ribosome precursors- main function More than one nucleolus can be present in the nucleus 3nucleoli , nucleus of the spinosum cell layer of skin 23 Nucleus

Electron Microscopically Nucleolus contains three distinct regions Fibrillar center transcription of rDNA takes place Dense fibrillar center most of the cleavage and post-transcriptional modification Granular center protein assembly on to ribosomal subunits takes place During cell injury fibrillar center and granular center gets separated 24 Nucleus

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25 Nucleus

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 26 Nucleus

Subnuclear bodies : 

Nucleus contains a number of non-membrane delineated bodies which are present in the nucleoplasm Subnuclear structures namely Cajal bodies PIKA bodies PML bodies Paraspeckles Speckles Subnuclear bodies 27 Nucleus

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MORPHOLOGY lymphocyte Eosinophil Neutrophil Type I,& II Alveolar cells Nucleus shapes – vary widely from spherical to bilobed and multilobed nuclei to ellipsoid and pear shaped nuclei 29 Nucleus

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Anucleated cells- which contain no nuclei, thus has no capacity to divide eg. RBC Platelets Polynucleated cells- With multiple nuclei eg. Species of protozoa Some fungi Intestinal parasites like giardia Giant cells in inflammation 30 Nucleus

Abnormal nuclear changes : 

Nucleus 31 Abnormal nuclear changes

Functions : 

Gene Expression- it involves replication & transcription (using DNA template to produce RNA) This RNA produced is pre-mRNA which then needs to be translated to ribosomes to form proteins. This mRNA is transported out via nuclear pores in a facilitated transport Cell compartmentalisation- nuclear envelope allows the nucleus to control its contents, and separate them from the rest of the cytoplasm where necessary Functions 32 Nucleus

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Where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus, where it interacts with transcription factors to downregulate the production of certain enzymes as in the pathway of glycolysis Prevents translation of unspliced mRNA Post Transcriptional Modification- newly synthesized pre-mRNA undergoes certain modifications before transported out to ribosomes in order to avoid its degradation. These are 5 capping, 3’polyadenylation and RNA splicing. Splicing involves removal of introns 33 Nucleus

Conclusively cell nucleus is the storehouse of everything what a cell shall do in future, since it handles the gene expression and overall metabolism of cellthus called “DIRECTOR OF CELL” : 

Conclusively cell nucleus is the storehouse of everything what a cell shall do in future, since it handles the gene expression and overall metabolism of cellthus called “DIRECTOR OF CELL” 34 Nucleus

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THANKS 35 Nucleus

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