Nucleus and nucleolus Dr Mah Jabeen Muneera Assistant
Nucleus and nucleolus Dr Mah Jabeen Muneera Assistant Professor Department of Anatomy KEMU
Introduction • • Command center DNA replication Synthesis & processing of RNA
Interphase Nucleus Location � Shape � Nuclear envelope and nuclear lamina � Chromatin � › DNA › RNA › Nucleoproteins � Nucleolus
Human genome project � Sequencing was successfully completed in 2003 � Entire length (1. 8 m) � Genetic information packaged in all 46 chromosomes. � 2. 85 -billion base pair sequence of nucleotides-- 23, 000 protein-coding genes.
Chromatin � DNA protein (histone & other structural proteins) complex � Euchromatin: › It is stretched out so that genetic information in the DNA can be read and transcribed � Heterochromatin: › Highly coiled or condensed form of chromatin, not available for transcription
The chromatin pattern is indicative of the metabolic activity of a cell � Liver cells and neurons- active in protein secretory activity – lightly stained nucleus due to euchromatin � Lymphocytes and sperm- inactive cells- darkly stained nucleus due to heterochromatin
Packaging of chromatin
Cell well being Dying cells have visible nuclear alterations. These include � karyolysis, � › Disappearance of nuclei due to complete dissolution of DNA by increased activity of DNAase � Pyknosis, › Condensation of chromatin leading to shrinkage of the nuclei (dense basophilic masses) � karyorrhexis, › Fragmentations of nuclei
Apoptosis
‘Female’Sex chromatin/Barr body � � � Discovered in 1949 by Barr and Bartram in the nerve cells of female cats X chromosome heterochromatin in an interphase cell Screening for X chromosome aneuploidies- buccal smears or blood smears Buccal- adjacent to the nuclear envelope Neutrophils- drumstick shaped appendage on one of the nuclear bodies
Sex chromatin bodies is one less than the number of X chromosomes syndrome karyotype Sex chromatin Nuclear sex Cytogenetic sex Klienfelters 47 XXY +ve female Turners 45 XO _ve male Female Superfemale 47 XXX + + female Female Jacobs 47 XYY _ve male
Nucleolus Three regions: � Fibrillar centers contain DNA loops of five different chromosomes (13, 14, 15, 21, and 22) that contain r. RNA genes, RNA polymerase I, and transcription factors. � Fibrillar material (pars fibrosa) contain ribosomal genes that are actively undergoing transcription and large amounts of r. RNA. � Granular material (pars granulosa) represents the site of initial ribosomal assembly and contains densely packed preribosomal particles.
Nuclear envelop and lamina
Nuclear lamina functions � Nucleoskeletal � Nuclear organization � Cell cycle regulation � Differentiation � Gene expression
Nuclear lamina and cell division � Phosphorylation of the nuclear lamins and other lamina-associated proteins ; Kinases � Proteins become soluble-- nuclear envelope disassembles � The lipid component -- cytoplasmic vesicles � chromosomes attach to the microtubules of the mitotic spindle
Nuclear lamina and cell division � Anaphase: Phosphatases are activated to remove the phosphate residues from the nuclear lamins � Telophase (early): Lamins repolymerize around each set of daughter chromosomes � Vesicles of lipid components and structural membrane protein components fuse. � Telophase (late): Formation of a nuclear envelope is complete
Impairment in nuclear lamina architecture � Emery Dreifuss Muscular Dystrophy
Size, Shape and orientation of the nucleus
Spherical nuclei of cuboidal cells
Oval Nuclei of Columnar cells
Stratified squamous epithelium
Exceptions � Nuclei pushed towards plasma membrane � Adipocytes � Mucous Acini
Binucleated cells
Binucleated cells e. g dome shaped surface cells of transitional epithelium
Multinucleated cells
Multinucleated cells
Multinucleated (Giant cells)
- Slides: 27