Nucleus: Structure and Function PDF

Nucleus: structure and function Joyjyoti Das, Ph.D. Assistant Professor  Learning outcomes  To gain knowledge on the structure and function of nucleus  Eukaryotic Nucleus - Structure Major co...

Nucleus: structure and function Joyjyoti Das, Ph.D. Assistant Professor  Learning outcomes  To gain knowledge on the structure and function of nucleus  Eukaryotic Nucleus - Structure Major components *An apparent amorphous mass enclosed by a nuclear envelope *Within: * Chromosomes * Chromatin * Nuclear matrix * Fibrillar network * Nucleoli * r-RNA and ribosomes * Nucleoplasm * Fluid of the nucleus The nuclear envelope *Components: * Two cellular membranes * Barrier to ions, solutes, macromolecules * Membranes fused to form pores * Complex assemblies of proteins * Outer membrane * Ribosomes * Continuous with RER *The nuclear envelope *Components: * Inner membrane * Bound to nuclear lamina * Filamentous network * Nuclear lamina * Supports envelope * Attachment of chromatin * Nuclear lamina fibers * Proteins – lamins superfamily – Intermediate filaments of cytoplasm.  Lamins are filamentous proteins in the intermediate filament family Lamin phosphorylation in prophase disassembles the nuclear lamina & allows for nuc. envel. Breakdown Laminins are extracellular proteins *The nuclear pore complex (NPC) *Large numbers of proteins – synthesized in cytoplasm and transported into the nucleus *RNAs manufactured in nucleus – transported to cytoplasm *The nuclear pore complex (NPC) *Huge macromolecular complex *Octagonal symmetry * 8-fold repetition of subunits * 30-50 proteins – nucleoporins *Nucleoporins * Symmetrical – on both cytoplasmic and nuclear sides FG Nups: phenylalanine and glycine repeats DNA in the nucleus  Nucleosome regulation of transcription integration of specific locus “body guards” of gene expression The nucleosomes resemble beads on a string, are further compacted into a helical shape via the NH2 terminal protein interactions of the octameric histones, called a solenoid.  Solenoid model The solenoid defines the packing of DNA as a 30nm fibre of chromatin and results from the helical winding of at least five nucleosome strands.