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BIOL 2020 > Cell Cycle > Flashcards

Cell Cycle Flashcards

(73 cards)

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1
Q

S phase events

A

Chromosomes duplicate so that two sister chromosomes are produced, held together by the centromere.

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2
Q

Interphase basic overview of events

A

G1 (growth and normal metabolism), S (DNA synthesis), G2 (growth and preparation for metabolism)

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3
Q

Cell cycle experiment

A

Radioactive thymidine added to an asynchronous cell culture for 30 minutes so that is incorporated into DNA, refresh media and wait, autoradiography to check for labeled DNA.

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4
Q

Cell cycle experiment observations

A

Mitotic cells: no labelled DNA
Only a fraction were labelled: S phase is short
30 min gap: There must be a phase between S and M (G2)

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5
Q

Prophase events

A

Centrosomes begin to condense
Centrosomes move to opposite poles
Nuclear lamina breaks down

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6
Q

Proteins involved in maintiaining compacted chromosomes

A
  • condensin
  • Cohesin
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7
Q

Condensin

A

organised DNA to maintain a condensed state, activated by phosphorylation by MPF

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8
Q

Cohesin

A

Holds the two sister chromatids together and runs the length of the centromere but lost from the arms in prophase (remains concentrated in the centromere.

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9
Q

Three roles of the kinetochore

A
  • attachment site between chromosomes and MTs
  • Location of some motor proteins later in anaphase
  • Involved in mitotic checkpoint
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10
Q

Kinetochore structure

A

Outer layer with enxtensive fibrous corona that uses connective proteins to attach to the collar around microtubules

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11
Q

Centrosomes cycle

A

G1 - one centrosome
S - duplication at right angle
Prophase - move to opposite sides

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12
Q

Three types of microtubules/spindle fibers involved in mitosis

A

Astral, chromosomal, polar

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13
Q

Nuclear lamina breaks down by ______, performed by ___

A

Phosphorylation, by Maturation Promoting Factor (MPF)

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14
Q

Prometaphase events

A

Mitotic spindle continues to develop
Chromosomes are moved to the center of the cell

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15
Q

Kinesin-related motor proteins function

A

Kinetochores attach to the MT side and then move the chromosome towards the plus end (away from the centromere)

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16
Q

Congression purpose

A

Movement of chromosomes to the metaphase plate, occurs during prometaphase

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17
Q

Congression mechanism

A

Rapid addition or loss of tubulin subunits from each side of the kinetochore attached MTs, with slow depolymerisation occuring at both centromeres.

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18
Q

Once at the equator, the cell determines that each chromosome is _______ and _______, then it will proceed to anaphase.

A

Bi-oriented, under tension
(the Spindle Assembly Checkpoint)

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19
Q

Syntelic attachment

A

Both spindles attached to the chromosome originate from the same centrosome

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20
Q

Monooriented chromsome

A

Only attached to one centromere (no tension yet)

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21
Q

Astral microtubules

A

Radiate outwards

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22
Q

Kinetochore (chromosomal) microtubules

A

attach to the sister chromatids

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23
Q

Polar microtubules

A

Overlap and do not attach to the sister chromatids

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24
Q

Anaphase events

A

Cohesin is cleaved and sister chromatids are pulled to opposite ends of the cell

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25
APC initiation of anaphase
MAD2 inhibits Cdc20 when chromosomes are not under tension, but once they are, Cdc20 will combine with multiprotein “Anaphase Promoting Complex,” and E3 ubiquitin ligase.
26
Securin
Normally inihibts separase, but will be destroyed via ubiquitination performed by APC(Cdc20-activated)
27
Separase
Activation leads to the cleaving of cohesin, allowing sister chromosomes to move to opposite poles of the cell.
28
MAD2 function
A kinetochore protein that inhibits the Anaphase Promoting Complex when chromosomes are not under tension
29
APC
An E3 ubiwuitin ligase that adds ubiquitins to proteins during anaphase
30
Anaphase A movements
chromosomes move towards the poles via the kinetochore MTs.
31
Anaphase B
Spindle poles move away from each other via polar MTs and astral MTs
32
Kinesin 13
A depolymerase that does not move and is attached to the kinetochore, aided by cytoplasmic dynein to help move the chromosome.
33
Kinesin-5
Walks the MT to the plus end of antiparallel polar microtubules to slide them apart and elongate the spindle via polymerisation.
34
Cytoplasmic dynein and astral microtubules
Link the astral MTs to the cell cortex and pulls the spindles poles inwards as it walks towards the minus end.
35
Telophase events
Chromsomes cluster at the opposite spindles Chromosome decondense Nuclear envelop reforms Spindle disassembles Golgi and ER reform
36
Protein for transition to telophase and G1
APC in combination with Cdh1
37
APC(Cdh1) function
Ubiquitinates some of the mitotic cyclins that bind kinases such as MPF that originally prompted the cell to enter mitosis, causing the cell to enter G1.
38
Contractile ring theory
Myosin II moves along a concentrated ring of actin in the cortex just below the cell membrane
39
Telophase midbody
Transient dense structure connecting two daughter cells at the end of cytokinesis with a role in localisation of abscission
40
Abscission
The final step in cytokinesis, the actual splitting of the two daughter cells.
41
Fusion exp 1: G1 rat and M HeLa cells
DNA in the G1 nucleus undergoes premature chromosomal compaction - there is a diffusible signal in the M phase cells.
42
Fusion exp 2: G2 rat with M phase HeLa
DNA in the G2 nucleus undergoes premature chromosomal compaction, too - there is 100% a diffusible signal in the M phase cells.
43
Fusion exp 3: S rat with M HeLa
DNA in the S nucleus begins to compact and is even pulverised because it is more vulnerable during replication; there is DEFINITELY a diffusible trigger.
44
Fusion exp 4: G1 cells and S cells
DNA in the G1 nucleus immediately starts to replicate; there is a diffusible signal in S phase.
45
Cdk stands for
Cyclin dependent kinases, phosphorylate other proteins but only when bound to a cyclin
46
Hartwell, Nurse and Hunt
Studied cdks in yeast; yeast; and sea urchins, earning a nobel prize.
47
G2 checkpoint
Mitotic cyclin + mitotic cdk = maturation promoting factor that phosphorylates serine and threonine residues to cause cells to enter mitosis.
48
Targets of MPF
condesins and lamins
49
Cyclin vs MPF concentrations over the cell cycle
cyclins must reach a critical point before the MPF activity starts
50
Fission yeast experiments use
Fission yeast reproduce by growing and dividing into equal sized cells, we can predict when they divide and the expected length.
51
Cdc2
The cdk of yeast cells (Cell Division Cycle)
52
Regulation of MPF activity
Occurs via phosporylation (the G2 checkpoint) Phosphorylation = inactive
53
Tyr 15
Phosphorylation on MPF acts like a brake
54
Wee1
Puts a phosphate on tyrosine 15
55
CAK
(cdk activating kinase) Puts a phosphate on threonine 161
56
Cdc25
removes the phosphate on tyrosine 15 to allow mitosis to proceed in yeast cells (it removes the brake)
57
Degradation of cyclins
performed by APCs specific to the checkpoint, inducing transitions between phases.
58
Mitotic cyclin degradation
Is performed by APC-Cdh1, sending the cell into G1. Mechanism - removes the phosphate from threonine-161
59
Wee1 mutation effect
Wee1 phosphorylates Tyr-15, therefore, loss of function will create shorter cells as there is no “brake”
60
Effect of Cdc25 mutation
Cdc25 removes the “brake” phosphate on Tyr-15, therfore, without the cell will not be able to enter mitosis and cells will be longer than normal.
61
Spindle assembly checkpoint components
APC-Cdc20 MAD2 Controls anaphase initiation
62
G1 checkpoint components
ATM Control activity of G1 cdk
63
G2 checkpoint components
Involved ATR Control the availability of Cdc25
64
START checkpoint
G1 checkpoint
65
ATM protein
Binds breaks in double stranded DNA and phosphorylates (activates) Chk2.
66
Chk2
Phosphorylates p53, stabilising the protein
67
p53
Phosphorylation stabilises the protein and allows it to trigger transcription of p21 or trigger apoptosis if the damage is irreversible
68
p21
Protein that inactivates G1-cdk so that DNA cannot proceed with replications before it is repaired
69
PUMA stands for
p52 upregulated modulator of apoptosis
70
PUMA function
Inactivates the antiapoptotic protein Bcl-2 (thus inducing function of BAX channel and apoptosis)
71
ATR
A protein that binds single stranded DNA breaks and downstream functions inhibit cdc25 so that mitosis is delayed to allow time for repair.
72
Ataxia telaniectasia syndrome
Mutations in the ATM or ATR genes that make individuals more prone to getting tumors and cancer, the cell cannot fix breaks in DNA and therefore radiation is not an ideal treatment
73
G0 phase overview
Cell leaves the cycle and may reversibly or irreversibly enter (quiescent or terminally differentiated)

BIOL 2020 (8 decks)

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