Lecture 7 - Nucleus Flashcards
What is the average size of a nuclear pore?
80nm
Where is the nuclear lamina located?
On the inner side of the inner nuclear membrane
What is the diameter of the nuclear pore complex?
9nm
How many large protein granules make up a nuclear pore?
8
What can pass through a nuclear pore?
Ions, small molecules, and proteins (
What is required for transport of larger molecules (>60kDa) across the nuclear membranes?
Nuclear pore receptor proteins (fibril associated)
Where to proteins that end up in the nucleus come from? What causes a protein to be directed to the nucleus?
Cytoplasm, Nuclear localization signals (NLS) that consist of a specific amino acid sequence on nuclear targeted protein
What type of transport is required to transport RNA and ribosomal subunits out of nucleus?
Active transport through NPCs
What proteins are required for active transport into the nucleus?
Importin, Ran-GTP (Ran bound to GTP)
What proteins are required for active transport out of the nucleus?
Exportin1, Ran-GTP (Ran bound to GTP)
What occurs to NPC during export or import?
It expands (up to 26nm)
What are the two forms of chromatin in the nucleus? What is unique about each?
Heterochromatin: Densely packed, transcriptionally inactive, stains dark in EM, LM appears as basophilic clumps of nucleoprotein
Euchromatin: Less densely packed, transcriptionally active, in EM appears electron-lucent (light section), appears lightly stained in LM
What are the nucleosomal histones? How many of each protein are in a single histone? How many times does a dsDNA strand wrap around a single histone?
- H2A, H2B, H3, H4
- 2 of each in a single histone (total of 8 proteins)
- dsDNA wraps around a single nucleosome approximately 2 times
What histone amino acids are responsible for binding DNA
Positively charged lys and arg
What is the role of H1?
Wraps around groups of nucleosomes forming 30nm diameter fibers (condensed chromatin).
What is the fundamental packing unit of chromatin? What makes up this fundamental unit?
Histone (an octamer made up of two copies of H2A, H2B, H3, H4)
At what interval (# of bp) do histones occur?
Approximately 200bp
What is a Barr body?
A condensed, transcriptionally inactive X-chromosome that is visible during interphase. Occurs only in females (since they have two copies of X chromosome).
How does the nucleolus stain?
Basophilic due to concentration of rRNA
What are the phases of interphase? How long does each phase typically last?
G1 (a few hours to several days), S (8-12hrs), G2 (2-4hrs)
During which cell cycle phase in the DNA replicated.
S
During which phase will cells take up tritiated thymidine?
S
Where is checkpoint 1 in the cell cycle? What cyclins allow the cell to pass checkpoint 1? What do these cyclins bind?
Within G1 (towards end), Cyclin G1 or Cyclin D binds to Cdk2
What cyclin binds to Cdk2 to start the S phase of the cell cycle?
Cyclin B
Phosphorylation at what sites activate Cdk2? Inactivate?
Activate: Thr161
Inactivate: Thr14, Tyr15
What makes up M-phase promoting factor?
Cyclin B-Cdk2 complex
Where is checkpoint 2? What allows the cell to pass checkpoint 2?
End of G2, dephosphorylation of Tyr15 and Thr14 on Cdk2
What is the function of the 26S proteasome? What is the significance of cyclin B degradation?
Disposes of degraded cyclin B, degradation of cyclin B causes MPF activity to cease
What are the “2 major” complexes of the cell cycle? What makes up each complex?
1) Start kinase (cyclinG1/cyclinD-Cdk2) 2) M-phase promoting factor (cyclin B-Cdk2)
What are the two primary methods to control cell cycle?
1) Regulation of genes that suppress cell proliferation
2) Regulation of growth factors that stimulate cell growth
What is the significance of the retinoblastoma (Rb) gene? What is the normal function of Rb?
Rb is a tumor supressor gene. A normal cell has 2 copies. Normal Rb prevents mitosis (entry into S phase).
What will occur if 1 copy of Rb is not functional? 2 copies?
If one copy is not functional, other copy will suppress increased proliferation (no significant change in phenotype). If both copies are not functional cancer of retinal cells will result.
What is the role of p53?
Acts prior to DNA replication to detect DNA damage and delay entry into S phase until damage repaired. If damage cannot be repaired cell will undergo apoptosis.
What are myc, fos, and jun? What characterizes this group of proteins?
Early response proto-oncogenes. Induced within 15 min of growth factor treatment, induction does not require protein synthesis.
Microtubules that radiate from centrosomes and function to separate the spindle poles and position them within the cell.
Astral microtubules
Microtubules that extend from each pole and overlap in middle of cell, responsible for pushing poles of cell apart.
Polar microtubules
What are the phases of mitosis?
Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis
What are caspases?
Family of proteolytic enzymes that drive apoptosis cascade.
Family of proteins that regulate mitochondrial membrane potential.
Bcl-2
Bcl-2 pro-apoptotic proteins
Bax, Bid, Bak, Bim
Bcl-2 anti-apoptotic proteins
Bcl-2, Bcl-W, Bcl-XL
What is the significance of mitochondrial membrane potential collapsing?
This causes the release of mitochondrial proteins cytochrome C oxidase and smac/DIABLO. These lead to caspase activation, which will ultimately lead to apoptosis.
