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HISTO - Exam 1 > Lecture 7 - Nucleus > Flashcards

Lecture 7 - Nucleus Flashcards

1
Q

What is the average size of a nuclear pore?

A

80nm

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2
Q

Where is the nuclear lamina located?

A

On the inner side of the inner nuclear membrane

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3
Q

What is the diameter of the nuclear pore complex?

A

9nm

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4
Q

How many large protein granules make up a nuclear pore?

A

8

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5
Q

What can pass through a nuclear pore?

A

Ions, small molecules, and proteins (

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6
Q

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

A

Nuclear pore receptor proteins (fibril associated)

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7
Q

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

A

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

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8
Q

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

A

Active transport through NPCs

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9
Q

What proteins are required for active transport into the nucleus?

A

Importin, Ran-GTP (Ran bound to GTP)

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10
Q

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

A

Exportin1, Ran-GTP (Ran bound to GTP)

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11
Q

What occurs to NPC during export or import?

A

It expands (up to 26nm)

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12
Q

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

A

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

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13
Q

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?

A
  • H2A, H2B, H3, H4
  • 2 of each in a single histone (total of 8 proteins)
  • dsDNA wraps around a single nucleosome approximately 2 times
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14
Q

What histone amino acids are responsible for binding DNA

A

Positively charged lys and arg

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15
Q

What is the role of H1?

A

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

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16
Q

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

A

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

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17
Q

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

A

Approximately 200bp

18
Q

What is a Barr body?

A

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

19
Q

How does the nucleolus stain?

A

Basophilic due to concentration of rRNA

20
Q

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

A

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

21
Q

During which cell cycle phase in the DNA replicated.

A

S

22
Q

During which phase will cells take up tritiated thymidine?

A

S

23
Q

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

A

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

24
Q

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

A

Cyclin B

25
Q

Phosphorylation at what sites activate Cdk2? Inactivate?

A

Activate: Thr161
Inactivate: Thr14, Tyr15

26
Q

What makes up M-phase promoting factor?

A

Cyclin B-Cdk2 complex

27
Q

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

A

End of G2, dephosphorylation of Tyr15 and Thr14 on Cdk2

28
Q

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

A

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

29
Q

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

A

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

30
Q

What are the two primary methods to control cell cycle?

A

1) Regulation of genes that suppress cell proliferation

2) Regulation of growth factors that stimulate cell growth

31
Q

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

A

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

32
Q

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

A

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.

33
Q

What is the role of p53?

A

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.

34
Q

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

A

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

35
Q

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

A

Astral microtubules

36
Q

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

A

Polar microtubules

37
Q

What are the phases of mitosis?

A

Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis

38
Q

What are caspases?

A

Family of proteolytic enzymes that drive apoptosis cascade.

39
Q

Family of proteins that regulate mitochondrial membrane potential.

A

Bcl-2

40
Q

Bcl-2 pro-apoptotic proteins

A

Bax, Bid, Bak, Bim

41
Q

Bcl-2 anti-apoptotic proteins

A

Bcl-2, Bcl-W, Bcl-XL

42
Q

What is the significance of mitochondrial membrane potential collapsing?

A

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

HISTO - Exam 1 (7 decks)

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