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Molecular Biology - Unit 2 - Zach H. > Cell Cycle 2 > Flashcards

Cell Cycle 2 Flashcards

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1
Q

What doe kinetochore microtubules attach?

A

> Attach each chromosome to spindle pole.

> Plus end of kinetochore microtubules are attached to sister chromatid pairs at large protein structures called kinetochores (located at centromere of each sister-chromatid) - and to centrosome.

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2
Q

What do interpolar microtubules do?

A

> Hold two halves of spindle together.

> Plus ends of interpolar microtubules coming from one pole interact with plus ends from other pole.

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3
Q

What do astral microtubules do?

A

> Interact with cell cortex.

> Astral microtubules radiate outward from the poles and contact the cell cortex helping to position the spindle in the cell.

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4
Q

Microtubules are nucleated from a specific location called what?

A

microtubule-organizing center (MTOC)

they grow on the plus end from the gamma-tubulin ring complex (gamma-TuRC) of the centrosome

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5
Q

What is the function of gamma-tubulin?

A

Involved in the nucleationg of microtubule growth.

Remember: Y-TuRC binds to negative end to nucleate and elongate microtubules

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6
Q

Where are microtubules nucleated?

A

At the centrosome at their minus end.

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7
Q

What does the protein organelle, centrosome, consist of?

A

Matrix and a pair of centrioles.

> contains gamma-TuRC greater than 50 copies of gamma-TuRC.
Centrosomes replicate with 2 pair of centrioles per centrosome.
Replicated centrosome splits and each centrosome migrates to form poles of mitotic spindle.

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8
Q

What are the two major types of motor proteins that move along microtubules?

A

> Dyneins

> Kinesins

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9
Q

Dynein

A

> tends to move to center of cell

> minus end directed microtubule motor

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10
Q

Kinesins

A

> tend to move to periphery of cell
walks toward plus ends of microtubules (most)
has 2 globular heads and elongated coil-coil tails
plays important role in chromosome separation

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11
Q

What proteins does the assembly and function of the mitotic spindle depend on?

A

Dyneins and Kinesins

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12
Q

What are the 4 major classes motor proteins involved in spindle assembly and function?

A

> dynein
kinesin-14
kinesin-5
kinesin-4,10

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13
Q

Kinesin 5

A

> 2 motor domains that interact with plus end of anti-parallel microtubule (interpolar microtubules).

> Moves these 2 anti-parallel microtubules past each other to force or push the spindle poles (centrosomes) apart.

> Movement: walks toward plus end - force centrosomes part.

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14
Q

Kinesin 14

A

> Minus oriented directed motor with a single motor domain.

> Movement: walks toward minus end - pulls poles together WOW! - so kinesin-5 is pushing poles apart while kinesin-14 is pulling the poles together!!!
Important: if no kinesin-5 then spindle collapses.

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15
Q

Kinesin 4,10

A

> Also called chromokinesins - plus directed motors.

> Push attached chromosomes away from the pole.

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16
Q

Push-Pull Chromosomes

A

> Plus end directed kinesin-4,10 motor proteins push chromosome as walking along interpolar or astral microtubule.

> kinesin-14 (minus oriented directed motor) pulls poles together while moving along kinetochore microtuble.

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17
Q

Dyneins

A

> minus end directed motors
link plus ends of asrral microtubules to actin skeleton at cell cortex
by moving toward minus end of microtubule, the dynein motors pull the spindle poles away from each other.

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18
Q

What does the kinetochore do?

A

Responsible for attachment of spindle to chromosomes.

Spindle microbubules are attached to each sister chromatid at the kinetochore.

This is a giant multilayered protein structure built on the chromosome.

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19
Q

What is the anchoring protein for attachment of multiple microtubules to the kinetochore?

A

Ndc80 complex

attaches kinetochore to plus end of microtubules

There is an exposed open end for addition and removal of tubulin subunits

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20
Q

What 3 forces are required for chromosome movement?

A

1) depolymerization
2) microtubule flux
3) polar ejection force

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21
Q

Force one: depolymerization. What is it?

A

> A major force pulls the kinetochore and chromosome toward the spindle pole.

> Depolymerization of the plus end of the microtubule drives the pulling of the kinetochore poleward (pulls kinetochore to pole).

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22
Q

Force two: microtubule flux. What is it?

A

> Microtubules are moved toward spindle poles while being dismantled at minus ends.

> Tubulin added at plus end while being removed at minus end - interpolar microtubules.

> Escalator

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23
Q

Force three: polar ejection force. What is it?

A

> Kinesin-4,10 motors on chromosomes interact with microtubules and transport chromosomes from poles.

> Results in push-pull phenomenon.

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24
Q

What happens in anaphase A?

A

Chromosomes move apart due to spindle microtubule depolymerization at kinetochore.

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25
Q

What happens in anaphase B?

A

separation of spindle poles themselves by kinesin-5 motor proteins; (alsodynein pulls pole apart).

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26
Q

What is the first visible change in the cell during cytokinesis?

A

Cleavage furrow

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27
Q

What underlies the cleavage furrow?

A

Contractile Ring

28
Q

What is the contractile ring composed of?

A

Actin and myosin filaments.

29
Q

What are the 4 stages of cytokinesis?

A

1) initiation
2) contraction
3) membrane insertion
4) completion

30
Q

Which 3 classes of extracellular signaling molecules regulate cell size and number?

A

> Class 1 - mitogens
Class 2 - growth factors
Class 3 - survival factors

31
Q

What is the function of mitogens?

A

Stimulate cell division by triggering G1/S-Cdk activity.

32
Q

What is the function of growth factors?

A

Stimulate cell growth.

33
Q

What is the function of survival factors?

A

Suppress form of programmed cell death known as apoptosis.

34
Q

If any of the 3 classes of extracellular signaling molecules that regulate cell size and number are aberrant, what is the result?

A

Cancer

35
Q

In the cell-cycle entry into S-phase, what do pathway do mitogens (class I) activate?

A

Mitogens activate the Ras-MAPK pathway.

This leads to increase of gene regulatory proteins including Myc.

Myc promotes entry into cell cycle by increasing expression of G1 cyclins.

36
Q

What does Myc promote?

A

Entry into cell cycle by increasing expression of G1 cyclins.

37
Q

What does G1-Cdk activate?

A

Group of gene regulatory factors called E2F proteins.

38
Q

What does E2F protein do?

A

Binds to promoters of G1/S cyclin and S cyclin genes (DNA synthesis).

39
Q

What protein inhibits E2F protein?

A

Rb protein (retinoblastoma)

> Shuts down entry int S phase of cell cycle.
Active G1-Cdk phosphorylates Rb to reduce binding to E2F.

40
Q

What happens if Rb protein is not working?

A

No control in going into cell cycle and so cancer can occur (retinoblastoma).

Loss of copies of both Rb genes leads to cell and tumor proliferation of retina.

41
Q

What two protein kinases are activated by DNA damage?

A

ATM and ATR protein kinases.

42
Q

When ATM and ATR protein kinases are triggered by DNA damage, what do they do?

A

> These kinases associate with the site of damage and phosphorylate Chk1 and Chk2 proteins (checkpoint kinase 1 and 2).

  • major target of Chk1/Chk2 is p53 which stimulates transcription of p21
  • p21 CKI binds to G1/S-Cdk and S-Cdk to inhibit activity (NO cell division - damaged DNA must be repaired)
  • BUT if this ATM/ATR system not working - it can cause cancer.
43
Q

Ataxia Telangiectasia (AT)

A

> ATM protein name comes from this disease, AT.
In humans, several radiation-sensitive or cancer-prone syndromes in which DNA damage checkpoint is disrupted: AT is one of them.
AT patients exhibit higher incidence of lymphoma and leukemia.
“Ataxia” of name means poor coordination.
“Telangectasia” of name means small dilated blood vessels.
Both symptoms seen in AT.
ATM protein is defective in AT; autosomal recessive.

44
Q

True of False:

Many mitogen activating genes identified as cancer-promoting genes or oncogenes.

A

True

45
Q

What percentage of caners have a Ras mutation?

A

30%

46
Q

What percentage of cancers have p53 mutation?

A

50%

47
Q

In animal cells, both cell growth and cell division depend on what?

A

Extracellular signals (growth factors and mitogens).

48
Q

What is the most important growth signaling pathway?

A

PI-3 Kinase Pathway

49
Q

What does PI-3 kinase do?

A

Adds ATP to inositol phospholipids.

50
Q

What protein adds ATP to inositol phospholipids?

A

PI-3 kinase

51
Q

What does the addition of ATP to inositol phospholipids by PI-3 kinase activate?

A

TOR (Target of Rapamycin) - which activates many factors for cell growth.

52
Q

What are the three mechanisms that coordinate cell growth with division?

A

1) Rate of cell division determined by extracellular factor leading to cell growth.
2) Cell growth and division controlled separately by growth factors and mitogens.
3) Cell growth and division both stimulated by extracellular factor.

53
Q

Cells in culture exhibit “density-dependent inhibition of cell division”. Why?

A

Depletion of mitogens - if you add fresh serum then the cells will proliferate again.

54
Q

What are myostain inhibitors being used to treat?

A

DMD

55
Q

Why is the function of myostatin?

A

Inhibits muscle cell growth.

56
Q

What are the four steps in mitosis?

A

1) condensation of chromosomes
2) assembly of mitotic spindle
3) breakdown of nuclear envelope
4) attachment of chromatids to spindle

57
Q

At the end of S phase, DNA molecules of duplicated chromosomes are a tangled mass. If sister chromatids were pulled apart at this stage, there would be breaks. What is the 2 step process to reorganize sister chromatids into short structures that can be pulled apart at anaphase with no breakage?

A

> Chromosome condensation (dramatic compaction).
Resolution (sister chromatids become distinct separate units)

brought about by condensin

58
Q

Condensin is a five subunit protein complex. What are the characteristics of these subunits?

A

> 2 SMC subunits (structural maintenance of chromosomes).

> 3 non-SMC subunits.

59
Q

What does condensin form?

A

Ring-like structure and uses ATP to promote compaction and resolution of sister chromatids.

60
Q

What is the mitotic spindle?

A

Bipolar array of microtubule proteins.

61
Q

What does the mitotic spindle do?

A

Pulls sister chromatids apart at anaphase.

62
Q

What triggers the assembly of the mitotic spindle?

A

M-Cdk triggers assembly of spindle.

63
Q

At what stage of the cell cycle does microtubules get organized?

A

mitosis stage

64
Q

What other protein is condensin related to?

A

Cohesin - the protein that holds sister chromatids together.

65
Q

Possible Essay Questions

A

1) Name 2 ways of regulating cyclin-Cdk complexes.
2) Describe the order of events involving APC/C, Cdc20, securin, separase, and cohesin in sister chromatids separates.
3) Describe the 3 forces driving chromosomes movement in cell division.
4) Describe all 3 checkpoints in the cell cycle.

Molecular Biology - Unit 2 - Zach H. (11 decks)

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