Chapter 10 - The Nucleus

separates the nuclear contents from the cytoplasm

nuclear envelope

this structure is continuous with the endoplasmic reticulum

outer membrane of the nucleus

the nuclear membrane contains this type of structure

phospholipid bilayer

the nuclear membrane is permeable to

small, nonpolar molecules

channels for small polar molecules, ions, and macromolecules

nuclear pore complexes

fibrous mesh that provides structural support to the membrane

nuclear lamina

intermediate filament proteins that associate to form higher order structures (like the nuclear lamina)

lamins

α-helical regions of 2 lamins wind around each other to form a coiled coil

formation of a dimer in the lamina

inherited tissue-specific disease caused by a mutation in lamin genes

Hutchinson-Gilford progeria

inner membrane proteins to which lamin binds

emerin, lamin B receptor (LBR)

connects lamin to the cytoskeleton

LINC protein complexes

composed of ~ 30 different pore proteins (nucleoporins)

nuclear pore complexes

small molecules and proteins (<40kd) pass through pore complexes by this mechanism

pass freely in either direction

proteins and RNAs pass through pore complexes by this mechanism

selective transport by recognition of specific signals

8 subunits (spokes) surround a central channel, with protein filaments extending from the ring to form a basket-like structure in the nucleus side

structure of a nuclear pore complex

amino acid sequence attached to proteins that must enter the nucleus

nuclear localization signals

these receptors recognize nuclear localization signals

nuclear transport receptors

single stretch of amino acids in rich basic amino acid residues (lysine, arginine)

T antigen nuclear localization signal

lysine-arginine sequence followed by a lys-lys-lys-lys sequence located 10 amino acids downstream

nucleoplasmin nuclear localization signal

receptors that recognize nuclear localization signals and carry proteins through the nuclear pore complex

importins

GTP-binding protein that controls directionality of movement

Ran

amino acid sequences that target proteins for export

nuclear export signals

receptors in the nucleus that recognize nuclear export signals and direct protein transport to the cytoplasm

exportins

family of nuclear transport receptors including importins and exportins

karyopherins

exportins form stable complexes with cargo proteins in association with _____ in the nucleus

Ran/GTP

GTP hydrolysis and release of _____ in the cytoplasm leads to dissociation of the cargo protein

Ran/GDP

releases mRNA on the cytoplasm side, ensures unidirectional transport

helicase

chromatin structure during mitosis

highly condensed (forms compact metaphase chromosomes

chromatin structure during interphase

decondensed, distributed throughout the nucleus

discrete region of the nucleus occupied by each chromosome

chromosome territory

type of chromatin that is transcriptionally active

euchromatin

type of chromatin that is not transcribed

heterochromatin

type of chromatin associated with the nuclear envelope and periphery of the nucleolus

heterochromatin

site where DNA replication occurs

replication factories

clustered sites where transcription occurs

transcription factories

organelles within the nucleus that concentrate proteins and RNAs

nuclear bodies

functions in rRNA synthesis and ribosome production

nucleolus

chromosomal regions containing 5.8S, 18S, and 28S rRNA genes around which the nucleolus is organized

nucleolar organizing regions

rRNAs required for ribosomal assembly

5.8S, 18S, and 28S

polymerase that performs transcription of 5.8S, 18S, and 28S RNA inside the nucleolus

RNA polymerase I

polymerase that performs transcription of 5S RNA outside the nucleolus

RNA polymerase III

regions of nucleoli

fibrillar center, dense fibrillar component, granular component

light region, contains genes encoding for rRNA

fibrillar center

borders the fibrillar center, processing of pre-RNA

dense fibrillar component

site of assembly of ribosomal subunits

granular components

type of rRNA that is transcribed outside of the nucleolus and produced elsewhere in the nucleus

5S rRNA

involved in assembly of snRNPs and other RNA-protein complexes

Cajal bodies

enzyme for RNA methylation (concentrated in Cajal bodies)

fibrillarin

location where snRNPs are transported after assembly and maturation in the Cajal bodies

speckles

speckles contain ____

splicing factors