nuclear structure and organization

How do nuclear compartments differ from cytoplasmic compartments?

They are not surrounded by other membranes

Translation happens in the ___ and DNA rep. Transcription and RNA processing happens in ___

cytoplasm

nucleus

The nuclear envelope comprised of

2 nuclear membranes

nuclear pore complexes

Underlying nuclear lamina (lamin proteins providing support of the nuclear mem)

The outer nuclear membrane (ONM) is continuous with the ___, and the peri-nuclear space between inner and outer nuclear membranes is connected to the ___

rER

ER lumen

The inner nuclear membrane (INM) is distinct from the ONM, and contains proteins that connect to the nuclear lamina

nuclear lamina

Nuclear pores form between ?

inner and outer nuclear membranes

The nuclear envelop controls traffic of proteins and RNAs through What?

through nuclear pore complexes to regulate gene expression

e.g. import of transcription factors export of mRNAs and ribosome components

8 subunits surrounding a central channel Is called

“Nucleoporins” (NUPs)

Describe Euchromatin

is decondensed and transcriptionally active. It is distributed throughout the nucleoplasm.

Describe heterochromatin

is highly condensed and not transcribed. It is often associated with nucleoli and the nuclear lamina

Lamina-associated domains (LADs):

heterochromatin associates with nuclear lamina.

Nucleolus-associated domains (NADs)

heterochromatin associates with periphery of nucleoli.

The genes within LADs and NADs are generally transcriptionally

repressed.

The Nucleolus: a ribosome factory For

rRNA transcription and processing, ribosome assembly

Tandem repeats of rRNA genes, very ___ transcription gives the tree-like appearance, which are made of ___

active

RNAs

RNA polymerase I what?

The most important

5S rRNA is *produced Where and by what?

outside nucleolus by RNA Pol III

Svedberg unit -

a unit of sedimentation coefficient, a measure of a particle's size, shape, and mass as it settles in a solution under centrifugal force

Newly transcribed 45S pre-rRNA acts as an organizing site for formation of new ?

nucleoli after mitosis

Internal transcribed spacers has to be___ and external transcribed spacer are regions btwn

Spliced out

repeats

Series of cleavages by proteins guided to pre-rRNA by small nucleolar ____and ___Followed by ~100 ribose methylations.

RNAs (snoRNAs) and snoRNPs.

Analogous to formation of spliceosomes on pre-mRNA by

small nuclear RNAs (snRNAs).

Conversion of uridine to pseudouridine (Ψ), sometimes called the 5th nucleotide.

Ψ =

methylated uridine.

ribosome assembly

1)rRNA associated with ribosomal proteins in the nucleolus (imported from cytoplasm)

2)40S and 60S subunits are exported separately to cytoplasm using exportin Crm1

ribosomal protein mRNAs are transcribed outside the nucleolus by RNA Pol II and exported to cytoplasm for translation.

Polycomb Bodies

Centers of transcriptional repression via methylation of histone H3, Lys27. Frequently associated heterochromatin.

Cajal Bodies

Assembly and storage of snRNPs involved in pre-mRNA splicing, other RNA-protein complexes. Also play a role in assembly of telomerase.

Speckles

storage of snRNPs and splicing factors. These are recruited to actively transcribed genes for pre-mRNA processing. Different Types of Nuclear

Nuclear Bodies: Nuclear Sub-Compartments with Distinct Functions

Chromatin domains

• Nucleolus

• Polycomb bodies

• Cajal bodies

• SpecklesMED204 – review hist

LAMINOPATHIES

Diseases resulting from mutations in nuclear lamins or in lamina-associated proteins

Removes the laminA cleavage site, so it remains anchored to the nuclear membrane. Causes problems with nuclear structure and the transcription of genes. May also cause problems with DNA repair

examples of laminopatheies

• Hutchinson-Gilford progeria syndrome (LMNA)

• Emery-Dreifuss Muscular Dystrophy

X-linked (emerin)

autosomal dominant (LMNA)

• Charcot-Marie-Tooth Disease Type 2B1 (LMNA)

• Dilated Cardiomyopathy (LMNA)

• Dunnigan-type Familial Partial Lipodystrophy (LMNA)

How is a progeria cell different than a normal cell

The structure of the nucleus changes

Abnormal splicing and removal of 50 amino acids from Lamin A protein results in loss of ___ cleavage site – ___cannot be removed

Zmpste24

Lipid Anchor

Explain progeria mutation

Mutation in gene for laminate A , farnesyl isn’t cleaved be no binding site for Zmpste so it can aggregate near the membrane

Lamin A:

Expression is regulated during development

Lamin C:

Alternatively spliced form of lamin A

Lamin B:

Expressed in virtually all somatic cells

Isoprenylation means what ?

diff length carbon chains that are added

phosphorylation means what?

important during onset of mitosis ; induces them to fall apart and allow nuclear membrane to dissolve

CaaX motif:

Cysteine, Aliphatic, Aliphatic, X

What does farnesyl = 15 Carbon create ?

Lipophillic motif so it can associate with membranes

Describe mechanism of when CAAX box is farnesylated

It allows lamin A to interact with the nuclear membrane on its own and after lamin a Associates with the membrane, It binds to other receptors like emerin and lamin B and farnesyl gets cut off

Nuclear Lamina Is composed of what?

Composed of lamins, intermediate filament proteins which form a cytoskeletal lattice or meshwork associated with the inner nuclear membrane

what is the transmembrane component of the LINC complex

Linker of Nucleoskeleton and cytoskeleton interacting with lamina

Architecture of the Nuclear envelope and Organization of its components are dependent on the

Nuclear lamina

FG-NUPs are the barrier to ___. Contain phe-Gly (F-G) repeats and facilitate ___between cytoplasm and nucleus.

permeability

regulated transport

What are importins

Proteins that enter the nucleus contain nuclear localization signals (NLS) that are recognized by special transport receptors

Fibrillation center

Gene encoding rRNA

Clear looking

Granular component

Assembly of ribosomal subunits

Dwane fibrillation component

Transcription of rRNA genes nucleolus organizing region

Nucleolus functions and number per nucleus

1-4

rRNA transcription, processing and ribosome assembly