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BIOC 341 > Lecture 20: Cell Cycle-overview and mechanics; mitosis; cytokinesis > Flashcards

Lecture 20: Cell Cycle-overview and mechanics; mitosis; cytokinesis Flashcards

1
Q

3 events of the Cell Cycle?

A
  1. cell growth and chromosome replication
  2. chromosome segregation
  3. cell division

Purpose:

  • Precisely duplicate the genetic material
  • Accurately distribute the replicated chromosomes into the two daughter cells
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2
Q

Four phases of the eukaryotic cell cylce?

A
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3
Q

Timing of a typical cell cycle

A
  • A typical human cell may have a cell cycle taking 24 hours.
  • 23 of those 24 hours are spent in interphase with 1 hr for M-phase (mitosis)
  • Within interphase, S-phase (DNA replication) may take 10-12 hours
  • The remaining intervals in interphase are the gap phases, G1 prior to S-phase and G2 following S-phase
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4
Q

___ are pauses that allow the cell to grow and respond to environmental cues.

A

gap phases

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5
Q

Gap phases

A
  • These are important decision making transitions. For example, the commitment to undergo another round of cell division occurs with a specific point in G1-called start or restriction point.
  • Transitioning this boundary commits the cell to fully cycle as it enters into DNA replication.
  • Cells may choose to enter a non-cycling, resting state called G0 (for day, week or years) until environmental condition become more favorable.
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6
Q

what are the 6 parts of the M (mitosis) phase?

A
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7
Q

Biochemical steps of mitosis

A
  • Chromosome condensation
  • Nuclear envelope breakdown
  • Replicated chromosome attach to the microtubule of the mitotic spindle
  • Chromosomes align on the metaphase plate
  • Chromosomes move to opposite poles
  • Chromosomes decondense
  • Nuclear envelope reforms
  • The cell is pinched in two by cytokinesis
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8
Q

Interphase

A
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9
Q

prophase

A

chromosomes condense, spindle migration continues, microtubule dynamic instability increases greatly

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10
Q

prometaphase

A
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11
Q

Metaphase

A

alignment of the microtubule attached chromosomes at the metaphase plate

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12
Q

Anaphase

A

sister chromatids synchronously separate

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13
Q

Telophase

A

daughter chromosomes arrive at the poles, nuclear envelope reforms, assembly of the contractile ring begins

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14
Q

Cytokinesis

A

cytoplasmic division

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15
Q

The mitotic spindle is a microtubule-based machine

A
  • The microtubule (MT) cytoskeleton and molecular motors kinesin and dynein are actively used to do work during mitosis.
  • MTs attach to chromosomes and to each other (through motors) to generate motion.
  • Specialized MTs called centrioles must duplicate to form the bipolar mitotic spindle
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16
Q

Centrisome duplication is triggered at the beginning of ____ by the activation of _____, which also triggers DNA replication

A

S-phase

G1/S-Cdk complex

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17
Q

Some cells, specifically higher plants and some vertebrate oocytes do not have centrisomes. In these cells, ______ are involved in forming the bipolar spindle.

A

motor proteins

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18
Q

What are the three classes of microtubules form the mitotic spindle?

A
  1. astral microtubules
  2. kinetochore microtubules
  3. overlap microtubules
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19
Q

Astral microtubules

A

– Radiate in all directions

– Contribute to forces that separate the poles

– Help orient and position the spindle

20
Q

Kinetochore microtubules

A

– Attach end-on to the kinetochore (which form at the centromere)

21
Q

Overlap mictrotubules

A

– Interdigitate at the equator

– Responsible for symmetry and bipolar shape of the spindle

22
Q

Bipolar plus-end directed motors, like ___, push the spindles apart

A

Kinesin-5

23
Q

Minus-end directed kinesin like ____ pull the spindles towards one another

A

kinesin-14

24
Q

Conventional plus-end directed kinesins like ____ attach chromosomes to MTs for positioning

A

Kinesins 4 and 10

25
Q

___ attach the astral MTs to the cell periphery and pull the spindles apart as the walk towards the minus end of MTs

A

Dyneins

26
Q

Influence of opposing motor proteins on spindle length

A
  • Kar3p (a kinesin-14) is a minus end motor protein
  • Cin8p (a kinesin-5) is a plus end motor protein
  • Too much Kar3p makes short spindles
  • Too much Cin8p makes long spindles
27
Q

Microtubule stability dramatically changes in mitosis.

A

-The normally stable cytoplasmic MT become shorter and more unstable

-This is a necessary change for the activities of mitosis

28
Q

____ stabilize microtubules

A

MAPs

29
Q

____ destabilize microtubules

A

catastrophins

30
Q

____ microtubules attach sister chromatids to MTs

A

kinetochore

31
Q

The ___ attaches the kinetochore to the plus end of microtubules

A

Ndc80 complex

32
Q

Microtubules capture kinetochores

A
33
Q

____ may help regulate bi-polar spindle attachment

A

Tension

34
Q

Tension may stabilize MT attachment

A
35
Q

What are the multiple forces that move chromosomes on the spindle?

A
  • Kinetochore generated poleward force
  • Polward microtubule flux
  • Polar ejection force
36
Q

Kinetochore generated poleward force

A

– Plus-end depolymerization at the kinetochore

– As the freed protofilaments curl outward, the push against the collar.

37
Q

Poleward microtubule flux

A

– While treadmilling dominates prior to anaphase (addition of tubulin at kinetochore matches tubulin removal at the spindle pole) a switch occurs and tubulin removal begins at the kinetochore

38
Q

Polar ejection force

A

– Plus end directed kinesins-4 and 10 attach to chromsomes at their ends and push away from the spindle pole.

39
Q

During metaphase (as an example of polward MT force) microtubules are said to ____ while the chromosomes are essentially stationary.

A

treadmill-growing at the plus end and shrinking at the minus end

40
Q

When does MT plux stop?

A

at the metaphase/anaphase transition

41
Q

chromatids seperate at ___

A

anaphase

42
Q

Major forces that separate daughter chromosomes at anaphase

A
43
Q

4 steps of cytokinesis?

A

• Initiation

  • Contraction
  • Membrane insertion
  • Completion
44
Q

The contractile ring is made of ____

A

actin and myosin filaments

45
Q

During cytokinesis…

A

interpolar microtubules split between the dividing cells as well as the matrix

46
Q

Assembly and contraction of the contractile ring are triggered by…

A

local activation of RhoA

47
Q

____ is required for cytokinesis

A

ESCRT III

BIOC 341 (24 decks)

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