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24 Cards in this Set

  • Front
  • Back
What is the nuclear matrix thought to do?
Organize the genome into domains that regulate gene expression and cell replication.
What are the three components of the nuclear matrix? What amount does each contribute to the total?
1. Nuclear Envelope/pore complex/lamina (~1-2%)
2. Nucleous (~1-2%)
3. Internal matrix (~98%)
What membrane encloses the perinuclear space? What is it continuous with? It is divided into segments, limited by:
Nuclear envelope. Continuous with the lumen of the ER. Nuclear pores divide it into segments.
Describe the contents of the Outer and Inner Nuclear Membrane
1. What it faces
2. What it contains
Outer Nuclear Membrane 1) faces the cytoplasm 2) contains ribosomes for protein translation
Inner Nuclear Membrane 1) faces nuclear lumen 2) contains integral proteins that bind to the nuclear lamina that in turn attach to marginal heterochromatin.
What is the diameter of the nuclear pores and what is the largest protein that can fit through?
Diameter = 10nm
Proteins smaller than 40kDa can fit through
Describe the structure/arrangement of each nucleoporin:
1. Gross arrangement
2. Number of proteins
1. Each pore has three strata of proteins arranged as an octamer (see pg25)
2. Over 100 different proteins involved
Nuclear localization signals target what part of the nucleoporin?
Cytoplasmic stratum serve as docking sites.
Describe the properties of NLS's
The have short amino acid sequences that contain positively charged basic amino acids (lysine [K] and arginine [R]).
Describe how importin is used to transport a nuclear protein into the nucleus
1. Importin-alpha binds the NLS of the nuclear protein
2. Together, they migrate to the nuclear pore where Importin-B binds a nucleoporin in the pore complex Ran-GTP
3. Energy dependent transport thru the pore
4. In nucleus, the protein is released from the importin, which is cycled back thru the pore complex.
In regard to phosphorylation, how can it be used to instigate proteins into the nucleus?
Dephosphorylation may be required for it to enter. OR phophorylation may be required to unmask the nuclear protein, releasing it.
What mediates the export of proteins out of the nucleus? What are its physical properties?
NES (nuclear export sequences). They are leucine-rich (e.g. LPPLERLTL)
Exportins are responsible for exporting what out of the cell?
RNA or Proteins
What mediates RNA export?
RNA binding proteins that are bound to exportin protein.
Are pores specific to the type of substance that they export? I.e. only protein or RNA?
No. They export both.
Describe how Ran-GTP coordinates migration of proteins into and out of the nucleus?
Proteins Targeted to Nucleus:
1. Nuclear import receptor binds cargo in cytosol
2. Together they migrate into the nucleus
3. Ran-GTP binds to the Importin/Cargo causing the cargo to be released in the nucleus
4. Ran-GTP charged importin migrates out of the nucleus
5. Ran-GTP is hydrolyzed, releasing importin back into cytosol.

Proteins targeted to the Cytosol:
1. Ran-GTP binds to empty nuclear import receptors; then to cargo
2. Together they migrate out of nucleus
3. In cytosol, GTP is hydrolyzed and complex falls apart, releasing all moieties.
4. Empty nuclear export receptors migrate back into the nucleus.
Describe/draw the Nuclear lamina and its relationships (p26)
1. Internally, marginal heterochromatin
2. Externally, inner nuclear membrane
3. Peripherally, pore complexes
What is the role of nuclear lamina during interphase? How thick is it? What happens to it during mitosis?
It maintains the nucleus as a sphere. It is 75 nm thick. During mitosis, the lamina breaks down due to hyperphophorylation of lamina proteins.
What are the lamina proteins? What does each interact with?
Lamin A, B, and C. A and C interact with marginal heterochromatin. Lamin B binds the inner nuclear membrane via Lamin-B Receptor - an integral membrain protein. A and C bind to Lamin-B, thereby anchoring heterochromatin to the inner nuclear membrane.
What is LMNA gene?
The gene that gives rise to Lamins A and C
What happens to the Lamin A, B, C and LBR complex during mitosis?
It falls apart but Lamin B remains bound to LBR to mediate re-formation of the nuclear envelope segments at the start of the next interphase.
What are laminopathies? Discuss the genetic behind it.
Inherited genetic disease that lead to premature aging. Caused by deletion of part of the gene that generates the splice that creates mRNA encoding lamin A.
What is the nucleolus the site for? How is it composed?
Ribosomal RNA production. It is comprised of 10 chromosomes, each with ~40 rRNA genes. Thus 400 rRNA genes.
98% of the nuclear matrix consists of the internal matrix. What does it mostly consist of?
Chromatin (i.e. DNA, histones (H1, H2A, H2B, H3 and H4) and non-histones (TFs, DNA and RNAs)
What are replicons? They were used (with tritiated-TdR pulse) to demonstrate what?
They are sites of DNA replication. With tritiated TdR pulse they showed that the nuclear matrix organize DNA replication bc replicons remained after nuclear matrix was striped of everything but the matrix.