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Foundations Week 7 > Cell Cycle I > Flashcards

Cell Cycle I Flashcards

0
Q

What phases collectively make up interphase?

A

G1, S, G2

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1
Q

What are the four phases of the cell cycle that occur sequentially and unidirectionally?

A

1 - Gap phase 1 (G1)
2 - Synthesis phase (S)
3 - Gap phase 2 (G2)
4 - Mitotic phase (M)

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2
Q

Cell reproduction begins with what?

A

the duplication of the cell’s components, including the exact duplication of each chromosome during S-phase
These are dividied equally between two daughter cells in M-phase

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3
Q

What are the G1 phase events?

A
  • important regulatory period
  • cells either commit to division during this time or exit the cell cycle (called G0 phase or qiuescence)
  • most cell growth occurs during this phase, must be coordinated with cell division
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4
Q

When is the first major cell cycle checkpoint? What happens here?

A

the G1/S-checkpoint or Start (aka Restriction Point)

- this is the point of no return; cells commit to cell cycle progression after passage through Start

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5
Q

What are the events of the S-phase?

A
  • important regulatory period
  • human cells need a similar amount of time in S-phase as they do in G1
  • chromosome replication
  • synthesize histones needed to compact the newly made chromatin
  • deposit cohesin along the chromosome arms to keep sister chromatid pairs together
  • duplicate the centrosome
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6
Q

What is the centrosome?

A

the microtubule nucleating center of the cell

*two centrosomes then facilitate assembly of mitotic spindle in M-phase

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7
Q

What occurs in G2-phase?

A
  • this is the transition period for the cell before committing to mitotic entry
  • during this time, cells continue to grow
  • G2 ends with a second major checkpoint, the G2/M checkpoint
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8
Q

When is the second major checkpoint of the cell cycle? What is the ‘commitment’?

A
  • the G2/M checkpoint

- passage through this checkpoint is the next point of no return, and cells will end the division process

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9
Q

What are the six sub-phases of M-phase (mitosis) events?

A 
1 - prophase
2 - pro-metaphase
3 - kinetochores on the chromosomes
4 - metaphase (within which is the 3rd major checkpoint - Spindle Assembly Checkpoint SAC)
4 - Anaphase
6 - Telophase
7 - Cytokinesis
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10
Q

Where does prophase stand in the M-phase? What occurs here?

A
  • first step, before pro-metaphase

- chromosome condensation occurs through the action of the condensin complex

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11
Q

Where does pro-metaphase stand in the M-phase? What occurs?

A
  • second step, after prophase, before kinetochores on the chromosomes
  • nuclear envelope breakdown occurs and microtubules that grow from the two centrosomes invade the nuclear space in search of capturing
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12
Q

What happens after the nuclear envelope breakdown occurs and microtubules grow from the two centrosomes invading the nuclear space? What are the microtubules looking for?

A

The microtubules look for and capture kinetochores on the chromosomes

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13
Q

Where in the sequence of M-phase does metaphase occur? What are its events?

A
  • after pro-metaphase and the capturing of kinetochores of the chromosomes by microtubules growing from the two centrosomes

In metaphase:

  • a diamond-shaped mitotic spindle forms and microtubules (which make up the spindle) move all chromosomes to the metaphase plate in an event known as congression
  • cells must pass the 3rd major checkpoint before transitioning to anaphase (Spindle Assembly Checkpoint, SAC)
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14
Q

When does the Spindle Assembly Checkpoint occur?

A
  • during metaphase of the M-phase
  • it is the third major checkpoint
  • cells must pass through this checkpoint to move on to anaphase
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15
Q

What is congression?

A

the movement of all chromosomes (by microtubules) to the metaphase plate

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16
Q

When does anaphase occur in the M-phase? What are the events?

A
  • after cells have gone through metaphase and the Spindle Assembly Checkpoint
  • sister chromatids disjoin and move toward opposite spindle poles
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17
Q

When does telophase occur in the sequence of M-phase? What are its events?

A
  • after anaphase (sister chromatids have separated and move toward opposite spindle poles) and before cytokinesis
  • cells exit M-phase as chromosomes decondense and nuclear envelopes reform around them
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18
Q

When does cytokinesis occur during M-phase? What are its events?

A
  • after telophase (chromosomes have decondensed and nuclear envelopes reformed around them)
  • an actin-myosin ring (aka the cleavage furrow) forms at the cell equator and contracts to pinch the cell into two smaller daughter cells
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19
Q

How do small organelles (such as mitochondria and lysosomes) form and separate into the two new cells during cell division?

A

small organelles are abundant and evenly distributed during distribution

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20
Q

How do large organelles (endoplasmic reticulum, Golgi apparatus) form and separate into the two new cells during cell division?

A

large organelles are fragmented into smaller vesicles during M-phase and reform in the next G1 phase

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21
Q

how long does it take most human somatic cells to divide in culture? Where is most of this time spent?

A
  • 18-20 hours
  • most of time is spent in G1 and S phases
  • less than an hour in M-phase
22
Q

How have early embryos evolved to meet the demand for rapid cell division?

A

they have evolved to meet this need by eliminating the Gaph phase (G1 and G2)
*division necessary every hour or less

23
Q

What is the significance of the first checkpoint (G1/S)?

A

fill

24
Q

What is the significance of the second major checkpoint (G2/M)?

A

fill

26
Q

What is the significance of the third major checkpoint (Spindle Assembly Checkpoint)?

A
  • between Metaphase and Anaphase of M-phase (Ana can’t call before checking with mother)
  • monitors kinetochore tension and inhibits the Anaphase Promoting Complex (APC)
  • when all kinetochores are under tension, then APC inhibition is relieved and the cell transitions to anaphase
27
Q

What three types of human cells are regularly used in the laboratory to study the cell cycle and division?

A
  • primary cells (normal cells; last 25-50 divisions after which they go into cell cycle arrest called replicative senescence)
  • immortalized cell lines (cells in culture that accumulate spontaneous mutations to avoid senescence usually requiring increased telomerase activity; they possess defects in certain cell cycle checkpoint machinery)
  • transformed cell lines (accumulated widespread genetic damage; immortalized cells that continue to divide in absence of serum, form tumors when injected in mice; not ideal for studying normal control of cell cycle, but useful for cancer cell biology)
27
Q

What are three methods of cell cycle analysis?

A
  • DNA staining with fluorescent dye and measuring DNA content per cell using a Flow Cytometer
  • Fluorescence-activated cell sorters (FACS machine)
  • FUCCI (microscopy-based)
28
Q

How does the following method of cell cycle analysis work:

staining DNA with a fluorescent dye and measuring DNA content per cell using a Flow Cytometer

A
  • cell cycle profiles can be obtained (histograms of DNA content)
  • most proliferating cells display a peak containing a 2C chromosome compliment (G1), broad valley in profile (S), and ending with a small second peak containing a 4C chromosome complement (mixture of G2 and M phases)
  • number of cells in each peak/region represents the fraction of cells in the population that are in a cell cycle stage
29
Q

How does the following method of cell cycle analysis work:

Fluorescence-activated cell sorters (FACS machine)

A

can be used to obtain identical profiles but can also physically sort the cells into different populations

30
Q

How does the following method of cell cycle analysis work:

FUCCI

A
  • a new microscopy-based method to visualize cell cycle phase in live cells
  • green fluorescent protein (GFP) or red fluorescent protein (RFP) is tagged to different cell cycle proteins whose levels oscillate throughout the cell cycle
  • in this assay, red cells are in G1 phase while green cells are S/G2/M-phase
31
Q

What is endoreduplication (or endocycles)?

A

a different type of cell cycle designed to increase DNA content without division

  • cells eliminate one Gap phase and M-phase
  • they alternate between one Gap phase and S-phase
  • successive chromosome doubling results in a massive increase in DNA content and cell size (called polyploidy)
  • due to numerous copies of genome, these cells can produce gene products in greater numbers
  • rare in humans, common in insect and plant cells
32
Q

What is an example of a human cell undergoing endoreduplication?

A

megakaryocyte: bone marrow cells that produce platelets and can synthesize up to 64 copies of the genome
* one megakaryocyte can produce thousands of platelets and releases them by cell eruption

33
Q

Dividing Drosophila Embryo

A

Single nucleus divides in a large embryo about nine times after which they migrate out and form the plasma sheath and divide about four more times
- happens without cytokinesis

34
Q

Hayflick Limit/Hayflick Phenomenon

A

the number of times a normal human cell population will divide until it stops
(limited because of telomeres; every replication, telomere is shortened; keeps going until senescence)

35
Q

What is the overall purpose of endoreduplication?

A

to increase biomass

multiple copies of genome

36
Q

What are some features of Cdk?

A
  • bilobed
  • when it has a ‘lip’ it is in its inactive state
  • activated by cyclin
37
Q

What does the Spindle Assembly Checkpoint do?

A
  • it monitors kinetochore tension and inhibits the Anaphase Promoting Complex (APC)
  • when all kinetochores are under tension, then APC inhibition is relieved and the cell transitions to anaphase
38
Q

What is the Anaphase Promoting Complex (APC)?

A
  • destroys cyclins
  • indirectly destroys “bracelets”/cohesin that hold sister chromatids together, allowing sister chromatids to separate –> cells can divide/separate
39
Q

Is action on cohesins by APC direct or indirect?

A

indirect

40
Q

What is the G1/S cyclin?

A

cycE which activates Cdk2

41
Q

What is the S cyclin? What does it bind?

A

cyc-A

binds Cdk1 or Cdk2

43
Q

What is the G2/M phase cyclin?

A

cycB
it binds Cdk1
Cdk1-cycB activate APC??

44
Q

Levels of cyclins rise and fall depending on the phase of the cell cycle. When is there high Cdk activity?

A

cycE: G1/S
cycA: active during S phase basically through G2 until M
cycB: G2/M until APC activity

45
Q

What are the events/mechanisms that regulate Cdk activity?

A

1 - changes in rates of cyclin gene expression
2 - changes in rates of cyclin degradation
3 - changes in phosphorylation state of Cdk
4 - inactivation by binding inhibitory proteins (G1 only)

FILL IN maybe make cards that ask what happens if one of htese goes wrong?

46
Q

in G1, all Cdks are inactive due to what three mechanisms?

A
  • suppression of cyclin gene expression
  • APC-mediated cyclin degradation (targets cyclins A and B)
  • high levels of Cdk inhibitors (CKIs)
47
Q

What triggers cyclin E expression (not an APC target)? What is the result of this?

A
  • signal (mitogen)
  • Cdk2-cyclin E activity rises immediately
  • this in turn activates Cdk1/2-cycA by promoting CKI destruction and APC inactivation
48
Q

What is a secondary result of cycE expression?

A

activation of Cdk1/2-cycA (by promoting CKI destruction and APC inactivation
*primary response is Cdk2-cycE activity

49
Q

What Cdk-cyclin activity promotes DNA replication?

A

Cdk1/2-cycA

50
Q

The cell cycle control system is based on what?

A
  • cyclin-dependent kinases (Cdk)
  • Ser/Thr protein kinases
  • these are regulated by cyclins
51
Q

When is cycB gene expression switched on?

A

towards the end of S-phase

52
Q

Though cycB gene expression is switched on towards the end of S-phase, Cdk1-cycB is held in an inactive state. What is this due to?

A

inhibitory phosphorylation
*abrupt removal of this phosphate by Cdc25 phosphatase at M phase triggers progression through G2/M checkpoint and mitotic events

53
Q

What Cdk-cyc complex stimulates activation of APC?

A

Ckd1-cycB

*APC is completely activated at the metaphase-anaphase transition

54
Q

What does APC promote?

A

sister chromatid disjunction and destruction of cyclins A and B
*this allows mitotic exit and maintains the G1-phase

Foundations Week 7 (10 decks)

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