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BIO130 > Week 12 - The Cell Cycle > Flashcards

Week 12 - The Cell Cycle Flashcards

1
Q

What happens in M phase?

A

The nucleus and cytoplasm divide; Mitosis and cytokinesis

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2
Q

What happens in Interphase?

A

It is the period between cell divisions; G1 phase, S phase, G2 phase.

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3
Q

What are examples of mature cells that don’t divide?

A
  • nerve cells

- muscle cells

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4
Q

Why can’t some mature cells divide?

A

As they become specialized they lose the ability to divide; stay in G0.

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5
Q

Example of a cell that only divides when given an appropriate stimulus?

A

Liver cells

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6
Q

What are 2 kinds of cells that normally divide on an ongoing basis?

A
  1. Hematopoietic

2. Epithelial stem cells

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7
Q

What is G0?

A

G0 is cell cycle exit; resting, no proliferation. Not dying, just not dividing or preparing to divide.

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8
Q

What are the 3 major checkpoints of the cell-cycle control system?

A
  1. Start checkpoint
  2. G2/M checkpoint
  3. Metaphase-to-anaphase transition (a.k.a. Spindle assembly checkpoint)
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9
Q

What happens at the Start Checkpoint?

A

Enter cell cycle and proceed to S phase; ask “Is the environment favourable?”

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10
Q

What happens at the G2/M Checkpoint?

A

Enter mitosis; ask “Is all DNA replicated?” and “Is environment favourable?”

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11
Q

What happens at the Metaphase-to-Anaphase Checkpoint/Transition?

A

Trigger Anaphase and proceed to cytokinesis; ask “Are all chromosomes attached to the spindle?”

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12
Q

What are the phases of Mitosis?

A

Prophase, Pro-metaphase, Metaphase, Anaphase, Telophase.

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13
Q

What 2 main things happen in prophase?

A
  1. Replicated chromosomes condense
  2. Mitotic spindle assembly starts and requires:
    - centrosome duplication
    - bipolar spindle assembly
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14
Q

What happens when a mitotic cell is fused with another cell in G1?

A

Proteins help chromosomes condense.

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15
Q

What happens when a mitotic cell is fused with another cell in S phase?

A

While trying to condense, it’s trying to pull apart to replicate; single strands get tangled and mess up.

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16
Q

What happens when a mitotic cell is fused with another cell in G2?

A

Proteins help chromosomes condense, and chromosomes are 2x as thick as G1 fusion.

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17
Q

What are chromosomes like at the end of G2?

A

At the end of G2, the replicated chromosomes are dispersed and tangled.

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18
Q

At the beginning of mitosis, how do chromosomes condense?

A

Condensin protein complexes aid in condensing.

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19
Q

At the beginning of mitosis, the sister chromatids are resolved but remain associated by what?

A

By cohesin at the centromere.

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20
Q

Why are dynamic microtubules required for mitosis?

A

They form the mitotic spindle.

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21
Q

In an interphase cells, how are microtubules arranged?

A
  • Microtubules are arranged in a radial pattern

- Minus ends are stabilized at the MTOC.

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22
Q

During Prophase, how are the microtubules arranged?

A
  • Bipolar mitotic spindle assembly starts

- Requires disassembly and reassembly of microtubules.

23
Q

What is the structure of a centrosome?

A
  • a pair of centrioles organized at RIGHT ANGLES to each other; composed of nine fibrils of three microtubules each
  • surrounded by pericentriolar material containing: gamma tubulin ring complexes (y) and y-TuRC’s
24
Q

In what phase does centrosome duplication start?

A

Starts in S phase.

25
Q

In what phase does Bipolar Mitotic spindle assembly start?

A

Starts in M phase.

26
Q

What kind of duplication is Centrosome duplication?

A

Semi-conservative.

27
Q

Each centriole serves as a template for what?

A

A template for a new centriole.

28
Q

How many times are centrosomes duplicated per cell cycle?

A

Only ONCE per cell cycle.

29
Q

Complete mitotic spindle assembly requires what?

A

Requires nuclear envelope breakdown.

30
Q

When does nuclear envelope breakdown occur?

A

Occurs at the boundary between prophase and prometaphase.

31
Q

What is the nuclear lamina?

A

Meshwork of interconnected nuclear lamin proteins.

32
Q

What is Lamin?

A

A special class of intermediate filaments that form a two-dimensional lattice on the inner nuclear membrane.

33
Q

What is thought to trigger nuclear breakdown?

A

The phosphorylation of lamins.

34
Q

What 3 things happen in Prometaphase?

A
  1. Mitotic spindle assembly is completed
  2. Chromosomes attach to spindle microtubules
  3. Chromosome movement begins.
35
Q

What is the structure of the mitotic spindle?

A
  • 2 centrosomes per cell
  • astral spindle microtubules help position mitotic spindle
  • polar spindle microtubules interdigitate towards the centre
  • chromosomal (kinetochore) spindle fibres attach at the centromere
36
Q

What 2 things does mitotic spindle assembly require?

A
  1. microtubule dynamics (disassembly and assembly)

2. microtubule motor protein activity (Kinesin and Dynein)

37
Q

Special kinesins at he bottom of a microtubule can do what?

A

Can walk to the plus ends of BOTH microtubules.

38
Q

What 3 things happen in metaphase?

A
  1. All chromosomes aligned on the metaphase plate
  2. microtubules from opposite poles are attached to kinetochores of sister chromatids
  3. Kinetochores are located at the centromere
39
Q

What are the 4 steps of chromosome alignment?

A
  1. Move DNA out of the way
  2. No tension
  3. Trial and error
  4. Pulling from both sides; tight grip as microtubules grow and shrink towards the centre
40
Q

The outer kinetochore of centrosomes like to bind near what?

A

Near the PLUS end of the microtubules.

41
Q

What is Tubulin flux through microtubules and how does it occur?

A
  1. Interdigitating microtubules slowly become radioactive
  2. other microtubules also become radioactive
  3. lengths stay the same; example of tread-milling (balanced additions and subtraction of heterodimers)
42
Q

What spindle microtubules will treadmill tubulin?

A
  • polar spindle microtubules

- kinetochore spindle microtubules

43
Q

What spindle microtubules will NOT treadmill tubulin?

A

Astral spindle microtubules.

44
Q

Why is the metaphase-anaphase transition an important checkpoint?

A

Anaphase will not start until all chromosomes are aligned on the metaphase plate.

45
Q

What are the 3 steps of Anaphase?

A
  1. Sister chromatids separate to form two daughter chromosomes; cohesin is cleaved.
  2. Chromatids pulled to opposite poles
  3. Kinetochore microtubules shorten.
46
Q

What cleaves the cohesin complex and allows sister chromatids to separate?

A

A Protease called Separase is activated to cleave cohesin.

47
Q

What triphosphate is required for anaphase?

A

GTP; need to assembly and disassemble microtubules to pull chromatids apart.

48
Q

What 2 things happen in Telophase?

A
  1. Nuclear envelope reassembly

2. Chromosome decondensation

49
Q

What happens in nuclear envelope reassembly?

A

Opposite of disassembly; Phosphostates de-phosphorylate lamins

50
Q

What happens in animal cell cytokinesis?

A
  • The cytoplasm is divided in 2 by a contractile ring of Actin and Myosin.
  • the interphase microtubules reform each daughter cell
  • marks the end of M phase
51
Q

What kind of filament does cytokinesis require?

A

Dynamic actin filaments.

52
Q

Steps of the contractile ring?

A
  1. Actin and myosin assemble to form ring
  2. ring squeezes and tightens until cell splits
  3. cleavage furrow: where the contractile ting is and where the cell splits in 2.
53
Q

Where is the contractile ring located?

A

At the cleavage furrow; INSIDE of cell, attached to the plasma membrane.

54
Q

In plant cells, how does cytokinesis occur?

A

By vesicle fusing together.

BIO130 (12 decks)

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