Chapter 10 - Nucleus

nuclear envelope function

separates the nucleus from the cytoplasm and controls protein and RNS traffic

how does the nuclear envelope control traffic

nuclear pore complexes

what are the components of the nuclear membrane

inner and outer membrane

what is the nuclear lamina made of

type 5 intermediate filaments

perinuclear space

fluid filled gap in between the inner and outer membranes; directly connected to the lumen of the ER

outer membrane

continuous with the endoplasmic reticulum (ER)

inner membrane

has integral proteins that bind to the nuclear lamina

what are the nuclear membranes made up of

phospholipid bilayer

what kind of molecules can passively go through nuclear membrane

nonpolar molecules

what molecules have to go through the nuclear pore complex

small polar molecules, ions, and macromolecules

how do lamins interacts with each other

lamins form a dimer through coiled-coil interactions between their α-helical region

how is the nuclear lamina formed

lamin dimers associate with each other to form higher order structures.

what is LINC

LInker of Nucleoskeleton and Cytoskeleton

where do lamins bind

inner membrane

what makes up the LINC comlpex

KASH and SUN

what are KASH and SUN

transmembrane proteins

two ways molecules move through NPCs

passive and selective transport

how many subunits do NPCs have

8

what is needed for selective transport

larger molecules such as proteins and RNAs, requires transport proteins and energy GTP

what is located in the NPCs to help move things through

FG repeats, glycine and phenylalanine

what must proteins have in order to enter the nucleus

nuclear localization signals

what recognizes nuclear localization signals

nuclear transport receptors

what are nuclear localization signals (NLS) rich in

K and R (lysine and arginine)

what two types of NLS are there

t antigen nls and bipartite nls

what is a bipartite nls

nls made of two amino acid sequences separated by another amino acid sequence

what is a t antigen NLS

an NLS that is one continuous stretch of amino acids

exportins and importins are part of what family

karyopherins

exportins

direct protein transport to the cytoplasm

nuclear export signals (NES)

an amino acid sequence that targets proteins for transport from the nucleus to the cytosol

importins

specialized transport proteins that carry specific molecules from the cytosol into the nucleus

know the import/export pathway

know exportin/cargo pathway

what does the karyopherin system transport

tRNA, rRNA, miRNA

how does mRNA get exported from the nucleus

uses an exporter complex to be brought through the NPC and once in the cytoplasm, helicase interacts with the export complex and removes it

what does the helicase ensure happens during mRNA transport

that helicase is removed, making transport unidirectional (makes sure the mRNA doesn't just go back through the NPC)

what does snRNA stand for

small nuclear RNA

what does snoRNA stand for

small nucleolar RNA

function of snRNAs

removes introns by splicing activity

what exports snRNA out of the nucleus

Crm1 is an exportin and complexes with snRNA

how is snRNP transported into the nucleus

snRNAs are exported by Crm1, once in the cytoplasm they disassociate. Crm1 binds to proteins in the cytoplasm to form snRNPs. snRNPs are imported by snurportin (importin) to the nucleus

what happens during mitosis

chromatin is highly condensed

what happens during interphase

chromatin decondenses and distributes

what happens during interphase

chromosomes occupy distinct regions, clustering

chromosome territory

each chromosome occupies a discrete region of the nucleus

when was chromosome territory official

1984 in drosophila salivary glands

what is fluorescence in situ hybridization (FISH)

a method for detection of rna or dna molecules within cells by hybridization with fluorescent probes

what is chromosome confirmation capture (3C)

a method where adjacent regions of chromosomes are identified by cross-linking

in what mitosis phase will there be euchromatin

interphase

in what mitosis phase will there be heterochromatin

interphase

characteristics of euchromatin

the chromosomes that are being expressed and transcribed, decondensed, dispersed throughout nucleus

characteristics of heterochromatin

highly condensed, not expressed/transcribed, located on the periphery of nucleolus clustered

what are LADs

lamina associated domains that associate with the nuclear lamina

what are NADs

nucleolus associated domain associated with the nucleolus

replication factories

a large complex containing clustered sites of DNA replication in eukaryotic cells

transcription hubs

a clustered site in the nucleus where transcription of multiple genes occurs

nuclear bodies

distinct, membraneless structures inside the nucleus made of rna and protein interactions

membrane-less regions of the nucleus where specific proteins and RNAs are concentrated to carry out particular functions

examples of nuclear bodies

nucleolus, cajal body, speckle, polycomb body

function of nucleolus

rRNA synthesis and ribosome production

what transcribes the 5.8, 18, and 28 subunits

rna polymerase l INSIDE the nucleolus

How are the major rRNAs (18S, 5.8S, and 28S) produced?

RNA Pol I transcribes them as one 45S pre-rRNA in the nucleolus, which is then processed into the three rRNAs

the 45S pre-rRNA is chopped into what three pieces

18, 5.8, and 28 subunits

how is 5S rRNA different

5S rRNA is transcribed separately by RNA Pol III outside the nucleolus

three regions of the nucleoli

fibrillar center

dense fibrillar component

granular component

what do the nucleoli regions represent

represents progressive stages of rRNA transcription, processing, and ribosome assembly

What chemical modifications occur during pre-rRNA processing?

methyl groups are added to bases and ribose residues

urine is converted to pseudourine

What is the role of snoRNAs in the nucleolus?

snoRNPs complex proteins, which then helps process and modify pre-rRNA into mature rRNAs.

What are snoRNPs?

snoRNA complexed with a protein

what is the function of snoRNAs

help with pre-rRNA processing and modification (processing of 45S pre-rRNA)

How do snoRNAs direct modifications of pre-rRNA?

snoRNAs base-pair with complementary rRNA sequences, guiding enzymes to specific sites for methylation or pseudouridine formation

How are ribosomal subunits assembled?

ribosomal proteins and rRNAs assemble in the nucleolus into pre-ribosomal particles, which are exported to the cytoplasm and mature into 40S and 60S subunits.

polycomb bodies

a complex of repressor proteins that methylate histone H3 lysine 27

what do polycomb proteins do

repress transcription by promoting methylation of lysine 27 on histone H3

what is used to visualized polycomb bodies

immunofluorescence

polycomb bodies

nuclear domains where polycomb proteins are concentrated

cajal bodies

a nuclear body involved in assembly of snRNPs and other RNA protein complexes

what is scaRNA

small Cajal body specific RNAs

function of scaRNA

guides ribose methylation and pseudo uridylation of snRNAs (like snoRNAs do)

what is another role of cajal bodies

used to make telomeres, which help lengthen and protect

speckle

a nuclear body that contains components of the mRNA splicing machinery