I principali compartimenti intracellulari di una cellula animale 15.1

Sequenze e Zone SEGNALE dirigono le proteine al corretto indirizzo cellulare

MARTEDI 27 NOVEMBRE BIOLOGIA ore 9.00 - 11.00

THE NUCLEUS Euchromatin (“normal”) 05_19_Interphase.jpg CHROMATIN Euchromatin (“normal”) Heterochromatin (highly condensed, ~10%)

Nucleus Structure About 10% of the cell volume Contains DNA - condensed and organized with proteins as chromatin Nuclear matrix – protein-containing fibrillar network Nucleolus - (pl. nucleoli) –rRNA synthesis, ribosome assembly Surrounded by nuclear envelope

Active chromatin = euchromatin appear lighter Inactive chromatin = heterochromatin is darker and located near periphery of nucleus Nucleolus a granular region site of ribosome assembly Interphase nucleus

Nuclear envelope (INVOLUCRO NUCLEARE): 2 lipid bilayer membranes, 10-50 nm apart the outer membrane is continuous with endoplasmic reticulum a denser layer of intermediate filaments, the nuclear lamina, is within the inner membrane composed of lamin proteins provides structure to nucleus heterochromatin binding site

12 year boy with progeria Defect in lamin A gene results in progeria – premature aging

I principali compartimenti intracellulari di una cellula animale

Il complesso del poro nucleare

Il complesso del poro nucleare

Nuclear Pores: ~3000/nucleus how the cell moves molecules into and out of the nucleus. At the pore, the inner and outer membranes come together forming an opening. Opening is lined with proteins: nuclear pore complex at least 34 different nucleoporin proteins, in octagonal symmetry (>500 total proteins) Including cytoplasmic filaments, extending to the cytoplasm

The role of nuclear pores Regulate transport of RNA and proteins into and out of nucleus Traffic is FAST! 1 typical human cell has to import 560,000 ribosomal proteins/minute, export 14,000 assembled ribosomes/minute Small molecules and proteins of less than 9 nm can pass freely Large proteins must be assisted Nuclear pores act as turnstiles

Nuclear Localization Signal (NLS) -Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val-

What happens when we alter the NLS? Kalderson, Roberts, Richardson, Smith (1984) Cell 39:p499. mutation

Another Experiment Microinjection Pipettes What happens when we use recombinant DNA techniques to add the NLS to a dummy protein? Normal or modified Bovine Serum Albumin (NLS added) and injected to the cytoplasm Microinjection Pipettes Normal BSA BSA with NLS

So What? This provided evidence of nuclear transport receptors family of proteins associated with the nuclear pore complex Importins recognize the NLS and bring proteins in Another set of proteins, the exportins, work in the opposite direction (These recognize other signals)

15_09_pore_transport.jpg NLS 15_09_pore_transport.jpg

15.4

L’involucro nucleare è disassemblato durante la mitosi