Lecture 7 - Nucleus

Question 1

What is the average size of a nuclear pore?

Answer 1

80nm

Question 2

Where is the nuclear lamina located?

Answer 2

On the inner side of the inner nuclear membrane

Question 3

What is the diameter of the nuclear pore complex?

Answer 3

9nm

Question 4

How many large protein granules make up a nuclear pore?

Answer 4

8

Question 5

What can pass through a nuclear pore?

Answer 5

Ions, small molecules, and proteins (

Question 6

What is required for transport of larger molecules (>60kDa) across the nuclear membranes?

Answer 6

Nuclear pore receptor proteins (fibril associated)

Question 7

Where to proteins that end up in the nucleus come from? What causes a protein to be directed to the nucleus?

Answer 7

Cytoplasm, Nuclear localization signals (NLS) that consist of a specific amino acid sequence on nuclear targeted protein

Question 8

What type of transport is required to transport RNA and ribosomal subunits out of nucleus?

Answer 8

Active transport through NPCs

Question 9

What proteins are required for active transport into the nucleus?

Answer 9

Importin, Ran-GTP (Ran bound to GTP)

Question 10

What proteins are required for active transport out of the nucleus?

Answer 10

Exportin1, Ran-GTP (Ran bound to GTP)

Question 11

What occurs to NPC during export or import?

Answer 11

It expands (up to 26nm)

Question 12

What are the two forms of chromatin in the nucleus? What is unique about each?

Answer 12

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

Question 13

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?

Answer 13

• H2A, H2B, H3, H4
• 2 of each in a single histone (total of 8 proteins)
• dsDNA wraps around a single nucleosome approximately 2 times

Question 14

What histone amino acids are responsible for binding DNA

Answer 14

Positively charged lys and arg

Question 15

What is the role of H1?

Answer 15

Wraps around groups of nucleosomes forming 30nm diameter fibers (condensed chromatin).

Question 16

What is the fundamental packing unit of chromatin? What makes up this fundamental unit?

Answer 16

Histone (an octamer made up of two copies of H2A, H2B, H3, H4)

Question 17

At what interval (# of bp) do histones occur?

Answer 17

Approximately 200bp

Question 18

What is a Barr body?

Answer 18

A condensed, transcriptionally inactive X-chromosome that is visible during interphase. Occurs only in females (since they have two copies of X chromosome).

Question 19

How does the nucleolus stain?

Answer 19

Basophilic due to concentration of rRNA

Question 20

What are the phases of interphase? How long does each phase typically last?

Answer 20

G1 (a few hours to several days), S (8-12hrs), G2 (2-4hrs)

Question 21

During which cell cycle phase in the DNA replicated.

Answer 21

S

Question 22

During which phase will cells take up tritiated thymidine?

Answer 22

S

Question 23

Where is checkpoint 1 in the cell cycle? What cyclins allow the cell to pass checkpoint 1? What do these cyclins bind?

Answer 23

Within G1 (towards end), Cyclin G1 or Cyclin D binds to Cdk2

Question 24

What cyclin binds to Cdk2 to start the S phase of the cell cycle?

Answer 24

Cyclin B

Question 25

Phosphorylation at what sites activate Cdk2? Inactivate?

Answer 25

Activate: Thr161 Inactivate: Thr14, Tyr15

Question 26

What makes up M-phase promoting factor?

Answer 26

Cyclin B-Cdk2 complex

Question 27

Where is checkpoint 2? What allows the cell to pass checkpoint 2?

Answer 27

End of G2, dephosphorylation of Tyr15 and Thr14 on Cdk2

Question 28

What is the function of the 26S proteasome? What is the significance of cyclin B degradation?

Answer 28

Disposes of degraded cyclin B, degradation of cyclin B causes MPF activity to cease

Question 29

What are the "2 major" complexes of the cell cycle? What makes up each complex?

Answer 29

1) Start kinase (cyclinG1/cyclinD-Cdk2) 2) M-phase promoting factor (cyclin B-Cdk2)

Question 30

What are the two primary methods to control cell cycle?

Answer 30

1) Regulation of genes that suppress cell proliferation | 2) Regulation of growth factors that stimulate cell growth

Question 31

What is the significance of the retinoblastoma (Rb) gene? What is the normal function of Rb?

Answer 31

Rb is a tumor supressor gene. A normal cell has 2 copies. Normal Rb prevents mitosis (entry into S phase).

Question 32

What will occur if 1 copy of Rb is not functional? 2 copies?

Answer 32

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.

Question 33

What is the role of p53?

Answer 33

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.

Question 34

What are myc, fos, and jun? What characterizes this group of proteins?

Answer 34

Early response proto-oncogenes. Induced within 15 min of growth factor treatment, induction does not require protein synthesis.

Question 35

Microtubules that radiate from centrosomes and function to separate the spindle poles and position them within the cell.

Answer 35

Astral microtubules

Question 36

Microtubules that extend from each pole and overlap in middle of cell, responsible for pushing poles of cell apart.

Answer 36

Polar microtubules

Question 37

What are the phases of mitosis?

Answer 37

Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis

Question 38

What are caspases?

Answer 38

Family of proteolytic enzymes that drive apoptosis cascade.

Question 39

Family of proteins that regulate mitochondrial membrane potential.

Answer 39

Bcl-2

Question 40

Bcl-2 pro-apoptotic proteins

Answer 40

Bax, Bid, Bak, Bim

Question 41

Bcl-2 anti-apoptotic proteins

Answer 41

Bcl-2, Bcl-W, Bcl-XL

Question 42

What is the significance of mitochondrial membrane potential collapsing?

Answer 42

This causes the release of mitochondrial proteins cytochrome C oxidase and smac/DIABLO. These lead to caspase activation, which will ultimately lead to apoptosis.