Chapter 10 (parts 1 and 2): The Nucleus

RNAs are transported to the cytoplasm as ___

ribonucleoprotein complexes (RNPs)

What do Karyopherin exportins transport?

tRNA, rRNA, miRNA

What does helicase do on the cytoplasm side?

releases mRNA and ensures unidirectional transport

mRNA transport does not involve ___ and is independent of ___

karyopherins

Ran

What exportin exports snRNA from the nucleus?

Crm1

In the cytoplasm, the snRNAs associate with proteins to form ___, which are recognized by an ___ and transported back to the nucleus.

small nuclear ribonucleoprotein particles (snRNPs)

importin

What is a mechanism for controlling protein activity in the nucleus?

regulation of protein transport

If ___ is phosphorylated and degraded by ___-mediated proteolysis, ___ can enter the nucleus and activate transcription of its target genes.

IkB

ubiquitin

NF-kB

What change does chromatin need during mitosis to form metaphase chromosomes?

become highly condensed

Is chromatin condensed or decondensed in interphase?

decondenses to distribute throughout the nucleus

DNA replication and transcription take place in ___ regions. How are these regions and DNA organized?

clustered regions

organized so transcriptional activity of gene is correlated with its position

What is a chromosome territory?

a discrete region of the nucleus that is occupied by distinct chromosomes

Compare and contrast euchromatin and heterochromatin.

Euchromatin: decondensed, transcriptionally active, distributed throughout the nucleus

Heterochromatin: highly condensed, transcriptionally inactive, associated with nuclear envelope or periphery of nucleolus

Genomes are divided into ___. Regions within a domain interact frequently with ___, but only rarely with regions in ___.

topologically associated domains (TADs)

one another

other domains

What are LADs and NADs?

LAD: lamina-associated domains

NAD: nucleolus-associated domains

DNA sequences found in ___ substantially overlap with those in ___. What kind of genes?

NADs

LADs

transcriptionally repressed (correspond to heterochromatin)

Transcription occurs at clustered sites called what?

transcription factories

What are nuclear bodies? Are they enclosed by membranes?

organelles within the nucleus that concentrate proteins and RNAs

no

What functions does the nucleolus serve?

rRNA synthesis and ribosome production

What directs transcription in the nucleolus? What ribosomes are involved? What ribosomal precursor RNA is involved?

RNA polymerase I

5.8S, 18S, 28S rRNA

45S ribosomal precursor RNA

Transcription of the 5S rRNA takes place where and with what?

outside the nucleolus

RNA polymerase III

Following each cell division, nucleoli become associated with the ___ that contain the ___, ___, and ___ ___ genes.

nucleolar organizing regions

5.8S

18S

28S rRNA

What is the structure of the nucleoli?

fibrillar center, dense fibrillar component, granular component

What functions do each of the regions of the nucleoli serve (4 regions)?

Fibrillar Center: genes encoding rRNA

Interface of Fibrillar Center and Dense Fibrillar Component: transcription

Dense Fibrillar Component: pre-RNA is processed

Granular Component: assembly of ribosomal subunits

Each nucleolar organizing region contains a cluster of tandemly repeated ___ genes separated by ___. What transcribes these genes?

rRNA

spacer DNA

RNA polymerase I

In higher eukaryotes, the primary transcript of rRNA genes is what? How is this processed?

45S pre-rRNA

processed via a series of cleavages (similar in all eukaryotes)

What are the two precursors to the formation of the 5S rRNA?

pre-RNA and ribosomal proteins

Where are ribosomal proteins produced and imported?

produced in the cytoplasm, imported to the nucleolus

What are used to form pre-ribosomal particles?

ribosomal proteins and 5S rRNA

Pre-ribosomal particles are exported to the ___, yielding the ___ and ___ ribosomal subunits.

cytoplasm

40S

60S

___ are involved in assembly of snRNPs and other RNA-protein complexes. snRNAs are modified by ___ and ___. The enzyme for RNA mehtylation (___) is concentrated in ___.

cajal bodies

ribose mehtylation and psuedouridylation

fibrillarin

cajal bodies

Following assembly and maturation in ___, snRNPs are transferred to ___, which also contain splicing factors.

cajal bodies

speckles

What are speckles recruited to?

actively transcribed genes where pre-mRNA processing occurs