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Trinity Term 1 > Regulation of the cell cycle > Flashcards

Regulation of the cell cycle Flashcards

1
Q

Describe the basic cell cycle

A

underlain by interphase and the M phase

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2
Q

Describe interphase

A
  • Gap 1 phase (sometimes containing the Gap 0 resting phase where the cell exits the cell cycle)
  • S phase
  • Gap 2 phase
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3
Q

What happens in the S phase of interphase?

A
  • replication of the genome
  • checks to ensure total and single replication occurs
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4
Q

Describe the M phase

A
  • mitosis
  • prophase
  • prometaphase
  • metaphase
  • metaphase–anaphse transition
  • anaphase
  • telophase
  • cytokinesis: cell division
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5
Q

Define mitosis

A

the equal separation of the genetic material into two daughter nuclei

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6
Q

Why must the cell cycle occur with high fidelity?

A

ensure the genetic identicality of daughter cells to parents

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7
Q

What does high fidelity mean in the mitotic context?

A

few errors in DNA copying and chromosome segregation

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8
Q

Describe perturbations to the cell cycle

A

mutation of proto-oncogenes resulting in inappropriate behaviour and triggering the development of cancerous cells and tumours

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9
Q

The rate maintenance of transcription and translation relative to size is controlled by

A

the nucleus

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10
Q

Describe cellular decision points

A

places in which there is an opportunity to halt or accelerate the progression

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11
Q

Give some cellular decision points

A
  • G1-S boundary
  • G2-M boundary
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12
Q

Describe the experimental approaches for regulator identification

A
  • mammalian cell fusions
  • embryonic cells (frogs, sea urchins)
  • genetics (yeast, Drosophila)
  • complementation and sequencing for orthology
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13
Q

Describe cell fusion experiments

A

uncover the dominant inducers of the cell cycle

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14
Q

How can dominance be established in cell fusion experiments

A

fusing two cells non-simultaneously derived that exist in different stages of the cell cycle

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15
Q

Describe the fusion of cells in S and G1 phases

A
  • results in the activation of the S phase in the originally G1 nucleus
  • S phase machinery is dominant to the G1 machinery
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16
Q

Describe the fusion of cells in the M phase and the G1 phase

A
  • M phase is activated in the originally non-M nucleus
  • dominance of M over non-M machinery
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17
Q

Describe decision points in egg maturation

A

mediated by MPF

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18
Q

MPF

A
  • Maturation Promoting Factor / Mitosis Promoting Factor
  • two subunits: a catalytic cyclin dependent kinase, and a regulatory cyclin B
  • implicated in decision making and promoting maturation into mitosis
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19
Q

Describe the action of MPF in maturing eggs

A
  • immature oocyte grows to complete Meiosis I
  • ejects first polar body of meiosis products
  • matures
  • initiated by a progesterone stimulus, and carried out by MPF
  • egg nucleus arrested in the initial metaphase of meiosis II (MPF highly active)
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20
Q

Describe mitosis post-fusion of the pronuclei

A
  • zygote undergo several rapid mitotic cycles
  • can be observed in Xenopus cells
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21
Q

Why do eggs arrest in metaphase of meiosis II?

A

relatively stable state of the condensed chromosomes

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22
Q

Describe what happens on experimental injection of mature egg cytoplasm from metaphase arrest into an immature oocyte in interphase arrest using a micropipette

A

results in Meiosis I completion, and the formation of a mature egg cell.

23
Q

What ceases the metaphase arrest?

A
  • fusion
  • cyclin degradation begins
  • facilitates congression of the cell cycle at the metaphase-anapahse transition
24
Q

Describe cyclin degradation

A
  • calcium induced
  • cell cycle regulating
25
Q

Describe cyclins

A
  • e.g. cyclin A and cyclin B
  • proteins that appear after fertilisation
  • concentration changes during the cell cycle progression
  • can be observed in sea urchins and surf clam proteomes under gel electrophoresis
26
Q

Describe the initial function of cyclins

A
  • activation of Cam-kinase II
  • ejection of the second polar body
  • completion of Meiosis II
27
Q

Describe the initial mitotic divisions of the zygote

A
  • omit G1 (including G0) and G2 phases
  • in the essence of rapidity
28
Q

Why must the egg be so large?

A
  • omission of G1 and G2
  • since division is not co-ordinated with growth, the sub-division cycles will each half the size of the egg
29
Q

Describe the action of Mitosis Producing Factor

A
  • not active in interphase
  • spikes in activity increasing in concentration to metaphase
  • decreasing to disappearance in anaphase
  • functional conservation
30
Q

Describe cdk

A
  • cyclin-dependent kinase
  • conserved across species
  • isolated using cdc28-temperature-sensitive cells grown at 25 degrees Celsius
31
Q

Describe the conservation of cdk

A
  • between sea urchins and yeast, as cdc2
  • not in frogs
32
Q

Describe the general composition of cdk1 and cdk2

A
  • N-lobe
  • pre C-helix hairpin
  • C-helix
  • activation segment
  • alpha-L12 domain
  • Cks1 domain
  • C-lobe
33
Q

Describe the discovery that the dynamics of cdk and cyclin accumulation and degradation are integral to driving the cell cycle.

A

When transformed with cdc28 and grown at 35 degrees Celsius, the cells in colony were found to be non-synchronised in various stages of the cell cycle.

34
Q

Describe cyclin and cdk in the cell cycle

A
  • unbound in G2, mitotic cyclin can bind to Cdc2 producing M-phase promoting factor
  • increase in cdk activity, and increase in cyclin B concentration, triggers mitotic onset
  • dissociates after M phase
  • proteolysis of cyclin B inactivates cdk, releasing Cdc2 back into the G1 phase, where it can bind the G1 cyclin to start kinase activity
  • dissociation at the S phase boundary
35
Q

Describe cdk2 in vivo

A

can perceived in its interactions with DHB on the nucleolar side using fluorescent tagging

36
Q

DHB

A

DNA helicase B

37
Q

Describe cdk2 activity across the cell cycle

A
  • low in G1 (including the G0) phase; very little is extra-nuclear
  • intermediate in the S phase (roughly equal spread between intra- and extra-nuclear DHB)
  • at high cdk2 activity, very little DHB is intra-nuclear: most is phosphorylated in the cytoplasm
38
Q

Describe cyclins and cdks across the cell cycle in mammalian systems

A
  • in G1, G1 and S-cyclin have the highest activity, alongside cyclin D and cdk4 and -6
  • in S, S-Cdk activity stays high, alongside cyclin A, E and cdk2 (the others drop)
  • throughout G2 M-Cdk activity increases alongside cyclin B and cdk1; it stays high until the metaphase-anaphase boundary
  • post-metaphase, there is little cyclin activity
39
Q

Describe yeast model systems of mitosis

A

there is substrate specificity between a single cdk and multiple cyclins.

40
Q

Describe cdk mechanics

A
  • reversible phosphorylation of serine or threonine residues of its multiple target proteins
  • uses a phosphate from ATP producing ATP, altering its properties allosterically, in order to co-ordinate the cell cycle
41
Q

What are the functions of cdk

A
  • regulation of chromatin structure
  • spindle and kinetochore formation
  • DNA replication
  • cytokinesis
42
Q

Describe the reverse cdk reaction

A

protein phosphatases release the molecule of inorganic phosphate on the residues.

43
Q

Describe the mechanics of cdk activation

A
  • partially activated by binding of the cyclin T-loop
  • fully activated upon phosphorylation of the bound T-loop
44
Q

Describe the effects of cdk activation

A
  • decision point
  • exponential increase in active kinase activating all substrates simultaneously, for an efficient transition
45
Q

Describe cdk inactivation

A
  • phosphorylation at an inhibitory site
  • wee1 kinase
  • reversed by cdc25 phosphatase
46
Q

What happens if cdks become inhibited?

A
  • cell cycle control is forgone
  • cells enter mitosis prematurely
  • become smaller and smaller
  • can be perceived under fluorescence microscopy, where dominant ‘wee’ mutants cause hyperactivity of Cdc2 cells
47
Q

Summarise phosphorylation control of cdk

A
  • binding of M-cyclin to cdk1 creates inactivate M-Cdk
  • action of CAK or wee1 creates an inactive M-Cdk with an inhibitory phosphate at the inhibitory region, and an activating phosphate and the activation site
  • action of cdc25 results in active M-Cdk
  • creates a positive feedback loop creating more inactive cdc25 phosphatase to be phosphorylated, and more wee1
48
Q

CAK

A

cdk-activating kinase

49
Q

wee1

A

cdk-inhibitory kinase

50
Q

Describe CKI proteins

A
  • block activity by wrapping around an active cyclin-Cdk complex
  • used on dsDNA damage (such as through x-rays), enacted by the inactivation of S-cdk in the G1 or S phases
51
Q

CKI proteins

A
  • cdk inhibitor
  • e.g. p27
52
Q

Describe the cellular response to dsDNA damage

A
  • ATM or ATR kinase activation
  • Chk1 or Vhk2 kinase activation
  • phosphorylating and activating p53, and releasing its Mdm2 group: stable and active and not degraded
  • used to transcribe the p21 gene and translate this transcript, expressing p21
  • wraps around an active G1-Cdks and S-Cdks, forming a complex and thus inactivating them
53
Q

Describe p53

A

ubiquitylation and degradation of proteasomes

54
Q

Describe p21

A

cdk inhibitor protein

Trinity Term 1 (38 decks)

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