InterphaseNucleus : InterphaseNucleus Largest cell organelle
Robert brown 1831 from roots of orchids, also coined the term
Slide 2 : Absent in RBCs & sieve cells
Was seen first by Leewenhoek ,1672 (from fish RBCs) & Fontana, 1781(skin of eels)
Can be studied under EM
Number : Number Generally cells are uninucleate, mononucleate or monokaryotic
2 / cell in Paramicium caudatum(micro-genetic & mega-somatic). Also in liver & cartilage cells
3 / cell in Paramecium aurelia-1 macro & 2 micro)
Multiple- /cell – striated muscles, latex cells, Opalina (protist) Ascaris, bone marrow(100), Rhizopus & some alga-Vaucheria
Syncytial and coenocytic conditions. Plasmodium in slime moulds
Size : Size It occupies 15-25 % space of cell mass.
Ploidy level, cell maturity and function determine size of the nucleus.
Thymus cell nucleus occupies 60% cell mass.
Parenchymatous cell nucleus occupies 10% of cell mass.
Dormant cells possess small sized nucleus.
5-25 µm general size.
Position : Position Generally at geomatric centre of cell.
Mature plants eccentric
Adipocytes peripheral
Glandular cells at the base
In spirogyra in the central vacuole where it is suspended by cytoplasmic strands.
Shape : Shape Round in young, rounded cuboidal or polygonal cells
Oval / elliptical – mature plant cells . Columnar animal cells.
Disc shaped- flat cells-squamous cells, endothelial cells.
Reinform/ kidney shaped- macronucleus of paramecium,
Horse shoe shaped- macronuleus of Vorticella
Bilobed- acidophill
Trilobed- basophill
Many lobed – neutrophil/ leucocytes
Long & moniliform- Stentor
Branched in silk spinning cells of larva of insect Plantyphylax
Chemical composition : Chemical composition DNA-9-12 %
BASIC PROTEINS (HISTONES)- 15 %
ENZYMES, ACID PROTEINS & NEUTRAL PROTEINS-65 %
RNAs – 5 %
Lipids – 3 %
Minerals (other than P)-Ca, Mg, K, Na- traces
Nuclear envelope, karyotheca, nucleolemma-Hertwig,1893 and pores : Nuclear envelope, karyotheca, nucleolemma-Hertwig,1893 and pores Double membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 (nm)-serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm.
Thickness- 60-90 Å
Outer mem-bear ribosomes on cytoplasmic surface and is connected with ER.
Inner surface is smooth
Perinuclear space-b/w outer and inner mem- 100-700 Å- continuous with channels of ER
Slide 9 : Nuclear pore- Callan & Tomlin-both membranes- inner and outer are continuous at pores
Number of pores-
150 / nucleus in mature RBCs of frog Xenopus laevis
30 million/ nucleus in its oocytes.
Pores are 400-1000 Å in diameter.
Circular /polygonal-octogonal in outline.
Pore contains-pore complex-blebs, diaphragm, septum, plug nucleoplasmin, microcylinders, annuli.
Pore comples consits of nine microcylinders--8 peripheral & one wider central central.
Nuclear pores are selective in penetration-allow new ribosomes out & not inside, proteins from cytoplasm allowed in but K, Na, / Cl does gain entry.
Slide 10 : Nuclear envelope breaks during division into small fragments /vesicles
New envelope dev from telophase from older envelope & ER.
Nucleoplasm / karyoplasm, nuclear sap : Nucleoplasm / karyoplasm, nuclear sap Strasburger , 1882.
Transparent, nonstainig, semi-solid colloidal complex.
Nucleotides, nucleosides, triphosphates, proteins, enzymes, minerals
Electron dense RNA granules & ribonucleoproteins (RNP) are abundant.
Nuclear matrix/ nuclear skeleton : Nuclear matrix/ nuclear skeleton Network of proteinaceous fibrils that traverses whole nucleus.
Form fibrous lamina/nuclear lamina- 150- 300 Å- underneath nuclear membrane.
Fibrous lamina is formed of three types of proteins- LAMINS A, B & C- LAMIN B remins attached with nuclear mem.
Proteins are acid proteins
Matrix helps in-holding telomere, in synapting pairing, turgidity of nucleus,
Chromatin : Chromatin Brightly stained-basic dyes-DNA HISTONE complexes-long & fine
Unit of chromatin is nucleosome.
Not present in the region of nuclear pores.
Euchromatin- transcriptionally active, loose coiling of nucleosomes, affected by pH, temp., hormones, poisons etc. replicates during S phase
Heterochromatin- inactive genes, darkly stained, false nucleolus, formed by solenoid type of coiling of nucleosomes-, replicate during LATE S phase / G 2 PHASE.
CONSTITUTIVE HETEROCHROMATIN- PRESENT IN ALL CELLS and at telomere and centromere and at the ends of genes, repetitive nitrogen base pairs
Facultative heterochromatin- develops secondarily meant for inactivating certain genes,
E.g. BARR body
Barr body(Barr & Bertmann,1949) : Barr body(Barr & Bertmann,1949) Mammalian females
One X becomes inactive during embryogenesis
Stains with orcein
20-50 % cells of oral mucasa/ 85% nerve cells have dark patch with nuclear envelope
Drum stick of nucleus of neutrophils (10% cells)
Generally number = (nX-1)
Human females -1, male -0
Super female-3X-1=2
Klinefilter syndrome-XXY=1
Y - SPOT : Y - SPOT QUINACRINE stained spot in the nucleus of mammalian males due to presence of heterochromatin in long arm of Y- chromosome
Nucleolus : Nucleolus Term by Bowmann,1848.
Naked membraneless, dark staining
Attached at NOR to chromatin
First observed by Fontanna,1781, studied by Wagner, 1840
1-4 general no.
13,14,15,20 & 21 chr have NOR/SAT
Xenopus oocyte has 1600 nucleoli
No nucleolus in sperm cells/ reticulocytes., blastomeres/ yeast/primitive algae
Calcium essential for maintaining it
Disappear during division & reappear after nuclear reformation.
Structure of nucleolus : Structure of nucleolus Homogenous/ vacuolate.
Following components:
Amorphous matrix/ pars amorpha-colloidal proteins
Granular part/pars granulosa-150-200 Å dia, protein & RNA made in ratio 2:1, precursors of ribosomes.
Fibrillar part-pars fibrillosa- 5-8 nm long fibrils of RNA.
Chromatin part-2 types- peri nucleolar & intra-nucleolar. Associated with synthesis of r RNA
45 S r RNA SPLITS in 18S, 5.8 S & 28 S r RNA
5 Sis transcribed elsewhere
Evidence of nuclear function : Evidence of nuclear function Enucleate part of amoeba cannot grow, divide & develop.
Hammerling,1934, Acetabularia mediterranea & A. crenulata.