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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
In what phase does Bipolar Mitotic spindle assembly start?
Starts in M phase.
26
What kind of duplication is Centrosome duplication?
Semi-conservative.
27
Each centriole serves as a template for what?
A template for a new centriole.
28
How many times are centrosomes duplicated per cell cycle?
Only ONCE per cell cycle.
29
Complete mitotic spindle assembly requires what?
Requires nuclear envelope breakdown.
30
When does nuclear envelope breakdown occur?
Occurs at the boundary between prophase and prometaphase.
31
What is the nuclear lamina?
Meshwork of interconnected nuclear lamin proteins.
32
What is Lamin?
A special class of intermediate filaments that form a two-dimensional lattice on the inner nuclear membrane.
33
What is thought to trigger nuclear breakdown?
The phosphorylation of lamins.
34
What 3 things happen in Prometaphase?
1. Mitotic spindle assembly is completed 2. Chromosomes attach to spindle microtubules 3. Chromosome movement begins.
35
What is the structure of the mitotic spindle?
- 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
What 2 things does mitotic spindle assembly require?
1. microtubule dynamics (disassembly and assembly) | 2. microtubule motor protein activity (Kinesin and Dynein)
37
Special kinesins at he bottom of a microtubule can do what?
Can walk to the plus ends of BOTH microtubules.
38
What 3 things happen in metaphase?
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
What are the 4 steps of chromosome alignment?
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
The outer kinetochore of centrosomes like to bind near what?
Near the PLUS end of the microtubules.
41
What is Tubulin flux through microtubules and how does it occur?
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
What spindle microtubules will treadmill tubulin?
- polar spindle microtubules | - kinetochore spindle microtubules
43
What spindle microtubules will NOT treadmill tubulin?
Astral spindle microtubules.
44
Why is the metaphase-anaphase transition an important checkpoint?
Anaphase will not start until all chromosomes are aligned on the metaphase plate.
45
What are the 3 steps of Anaphase?
1. Sister chromatids separate to form two daughter chromosomes; cohesin is cleaved. 2. Chromatids pulled to opposite poles 3. Kinetochore microtubules shorten.
46
What cleaves the cohesin complex and allows sister chromatids to separate?
A Protease called Separase is activated to cleave cohesin.
47
What triphosphate is required for anaphase?
GTP; need to assembly and disassemble microtubules to pull chromatids apart.
48
What 2 things happen in Telophase?
1. Nuclear envelope reassembly | 2. Chromosome decondensation
49
What happens in nuclear envelope reassembly?
Opposite of disassembly; Phosphostates de-phosphorylate lamins
50
What happens in animal cell cytokinesis?
- 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
What kind of filament does cytokinesis require?
Dynamic actin filaments.
52
Steps of the contractile ring?
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
Where is the contractile ring located?
At the cleavage furrow; INSIDE of cell, attached to the plasma membrane.
54
In plant cells, how does cytokinesis occur?
By vesicle fusing together.

BIO130 (12 decks)

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