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BMS241 final exam > Topic 10 - The Cell Division Cycle > Flashcards

Topic 10 - The Cell Division Cycle Flashcards

1
Q

What are the 4 phases of the cell cycle?

A
  1. M phase
  2. G1 phase
  3. S phase
  4. G2 phase
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2
Q

In simple terms, what processes occur in the M phase?

A

mitosis - nucleus divides

cytokinesis - cell splits in 2

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3
Q

In simple terms, what processes occur in the S phase?

A

(S = synthesis) - cell replicates nuclear DNA

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4
Q

What is interphase?

A

period between one M phase and the next (includes G1, S & G2 phases)

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5
Q

In simple terms, what processes occur in the G1 phase?

A

interval between end of M phase & start of S phase - make sure that internal and external environment conditions are suitable for S & M phases

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6
Q

In simple terms, what processes occur in the G2 phase?

A

interval between end of S phase & start of M phase - make sure that internal and external environment conditions are suitable for S & M phases

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7
Q

Cell - cycle control system has 3 checkpoints. what are they?

A
  • checkpoint in mitosis - are all chromosomes properly attached to the mitotic spindle? -> pull chromosomes apart
  • checkpoint in G1 - are environmental conditions favourable? -> proceed to S phase
  • checkpoint in G2 - is all DNA replicated? Is all DNA damage repaired? -> proceed to M phase
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8
Q

The proteins of the cell-cycle control system first appeared…?

A

> 1 billion years ago

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9
Q

Which ‘switch’ mechanisms are used in the cell-cycle control system to activate/deactivate key proteins & protein complexes?

A

phosphorylation - protein kinases

dephosphorylation - protein phosphatases

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10
Q

Switching these kinases on and off at the appropriate times is partly the responsibility of another set of proteins in the control system—the …?

A

cyclins

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11
Q

The kinases of the cell-cycle control system are therefore known as

A

cyclin-dependent protein kinases (Cdks)

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12
Q

How We Know: The first components of the cell-cycle control system to be discovered were the cyclins and cyclin-dependent kinases (Cdks) that drive cells into M phase how?

A

Xenopus frog eggs

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13
Q

How We Know: M cyclin was initially identified as a protein whose concentration rose gradually during interphase and then fell rapidly to zero in which organism?

A

clams

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14
Q

Activity or levels of cyclins and cyclin-dependent kinases (Cdks) would be highest/lowest in which phase?

A

highest in M phase

lowest in interphase

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15
Q

T or F - Cyclins are regulatory subunits whose concentrations stay the same during the cell cycle

A

false - they vary in different cycles

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16
Q

Maturation Promotion Factor (MPF) = ?

A

cyclin-dependent protein kinases (Cdks)

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17
Q

Do Cdks also vary in [ ] during course of the cycle?

A

no - they stay constant

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18
Q

So what triggers the abrupt activation of these cyclin–Cdk

complexes?

A

For a Cdk to be active, it must be phosphorylated at one site and dephosphorylated at two other sites

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19
Q

The cyclin that acts in G2 to trigger entry into M phase is called …?

A

M cyclin

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20
Q

Re. THE MAJOR CYCLINS AND CDKS OF VERTEBRATES as in MCQ… which C-Cdk complex combines with which cyclin? (cyclin-A, B, D & E) put them in alphabetical order
(remember ‘small eggs’ - where these guys were initially found & studied)

A

S, M, G, G/S (small eggs)

A, B, D, E

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21
Q

Before M phase, M-Cdk phosphorylates certain certain factors. List them (think about what happens in M phase)

A
  • Lamins -> nuclear envelope breakdown
  • Nuclear pore proteins -> nuclear breakdown
  • MTs -> formation of M spindles
  • Histones -> DNA packing into chromatin
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22
Q

The Cell-Cycle Control System Also Depends on Cyclical

Proteolysis via what mechanism?

A

Ubiquitylation of a cyclin

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23
Q

When cells enter G0 phase (non-proliferating state), they can remain there for day weeks and even for the lifetime of the organism!

A

cool fact

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24
Q

Once past the G1 checkpoint, a cell usually proceeds all the way through the rest of the cell cycle quickly. In mammals, this typically takes how long?

A

12 - 24 hours

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25
Q

Why is the G1 checkpoint is sometimes called ‘Start’?

A

because passing it represents a commitment to complete a full division cycle

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26
Q

Which 2 cells in the human body enter irreversible G0 state in which the cell-cycle control system is largely dismantled?

A

nerve cells

skeletal muscle cells

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27
Q

S-Cdk Initiates DNA Replication and Helps Block Re-Replication. how? (hint: origin of replication…)

A

pre-initiation complex, which includes: origin recognition complex (ORC) + origin of replication + Cdc6 cyclin

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28
Q

What Help Hold the Sister Chromatids of Each Replicated Chromosome Together? What phase are they found?

A

cohesin rings

DNA replication in S phase -> late M phase

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29
Q

DNA Damage Checkpoints Help Prevent the Replication of Damaged DNA. there are 2. how do they do this? (figure 18-16) really good! for the 1st…

A

1st checkpoint: DNA damage -> ++p53 (activated by protein kinase) -> DNA -> p21 mRNA -> p21 (Cdk inhibitor protein) -> G1/S-Cdk and S-Cdk inactivating them -> cell cycle arrest in G1
2nd checkpoint: DNA damage -> phosphatese inhibited -> cannot remove inhibitory phosphates from M-Cdk -> M-Cdk remains inactive -> M phase cannot be initiated

30
Q

Persistent p53 activity eventually leads to …?

A

apoptosis

31
Q

Cells lacking p53 function are especially prone to …?

A

cancer

32
Q

How long does M phase usually take in mammals?

A

1 hour

33
Q

What Drives Entry Into M Phase and Mitosis?

A

protein complex M-Cdk

34
Q

What activates protein complex M-Cdk? ie. removes inhibitory phosphates holding M-Cdk activity in check?

A

protein phosphatase (Cdc25)

35
Q

What increases protein phosphatase (Cdc25) levels that drive cell from G2 abruptly -> M phase?

A

+ ve feedback mechanism driven by ++activated M-Cdk

36
Q

What do condensins do? Condensins are structurally related to which other molecule?

A

chromosome condensation (assemble on each individual chromatid) & are structurally related to cohesins (rings that hold sister chromatids together)

37
Q

The mitotic spindle carries out what? what is the component?

A

mitosis via microtubules

38
Q

the contractile ring carries out what? what is the component?

A

cytokinesis (pinching the cell into 2 daughter cells) via actin & myosin filaments

39
Q

Which stages constitute mitosis?

A

prophase, prometaphase, metaphase, anaphase, telophase

40
Q

cytokinesis begins in which phase to which phase?

A

anaphase to telophase

41
Q

Describe all events in mitosis…

A
  • PROPHASE - chromosomes condense & mitotic spindles assemble between centrosomes
  • PROMETAPHASE - nuclear envelope breaks down & chromosomes attach to spindle MTs
  • METAPHASE - chromosomes aligned at ‘equator’
  • ANAPHASE - sister chromatids synchronously separate
  • TELAPHASE - two sets of chromosomes arrive at the poles of the spindle. A new nuclear envelope reassembles around each set -> marks end of mitosis
42
Q

Before M phase begins, two critical events must be completed: what are they?

A

DNA must be fully replicated, and, in animal cells, the centrosome must be duplicated

43
Q

Centrosome duplication begins at the start of which phase?

A

S phase

44
Q

what is the centrosome cycle?

A

process of centrosome duplication and separation

45
Q

What are centrosomes called during mitosis?

A

spindle poles

46
Q

What are the radial array of MTs formed after centrosome replication?

A

asters

47
Q

When do mitotic spindles form?

A

prophase

48
Q

The activation of what factor initiates prophase?

A

M-Cdk activation

49
Q

In humans, each kinetochore is bound by ? MTs In yeast?

A

humans - 20 - 40

yeast - 1

50
Q

Three classes of microtubules make up the mitotic spindle are?

A
  1. aster
  2. kinetochore
  3. interpolar
51
Q

T or F - Chromosomes Aid in the Assembly of the Mitotic Spindle (esp. in plant cells without centrosomes)

A

true

52
Q

Proteolysis of which structure Triggers Sister-Chromatid Separation and the Completion of Mitosis?

A

cohesin via separase (securin is targeted by anaphase promoting complex - APC) -> to un-inhibit separase

53
Q

Difference between anaphase A & B?

A

anaphase A - kinetochore MTs shorten -> daughter chromosomes are pulled toward opposite poles
anaphase B - elongation of interpolar microtubules -> spindle poles move apart -> daughter chromosomes are pulled toward opposite poles

54
Q

Unattached Chromosomes Block Sister-Chromatid Separation via which factor? eg. of pathology where this mechanism fucks up…

A

block activation of APC (anaphase promoting complex)

e.g. Down Syndrome: Triploidy of chromosome 21

55
Q

The Nuclear Envelope Re-forms at Telophase via phosphorylation or dephosphorylation?

A

dephosphorylation

56
Q

Cytokinesis depends on which cytoskeletal factors?

A

actin & myosin

57
Q

The Contractile Ring of Animal Cells Is assembled in which phase?

A

anaphase

58
Q

Animal & plant cytokinesis is different how?

A

Animal cytokinesis involves a contractile ring

Plant cytokinesis in volves a new cell wall

59
Q

phragmoplasts & Golgi filled with polysaccharides and glycoproteins help do what in plants?

A

build a new cell wall during cytokinesis

60
Q

Cells cannot generate some membrane-enclosed organelles de-novo…these include…?

A

Mitochondria
Chloroplasts
Endoplasmic reticulum
Golgi apparatus

61
Q

What % of neurons in the CNS die of apoptosis?

A

50%

62
Q

Difference between apoptosis & necrosis?

A

Necrosis is inflammatory (cell membrane is ruptured and cytoplasmic proteins go to the extracellular space)
Apoptosis is not inflammatory (Cytoplasmic proteins are never free in the extracellular space) - a clean process

63
Q

Molecular process of apoptosis… figure 18-39

A

2 inactive procaspase molecules -> cleavage via protease -> active caspase X molecule (2 sml subunits & 2 lge subunits) -> cleavage & amplification of many more caspase Y -> even more caspase Z in exponential way

64
Q

the Bcl2 Family of Intracellular Proteins does what?

A

regulate apoptosis

65
Q

Describe apoptotic regulation…figure 18-40 (flowers of death)

A

apoptotic stimulus -> mitochondrion -> activated Bax or Bak -> cytochrome C release -> activates adaptor protein (1 death ‘petal’) -> assembly into the flower of death (apoptosome) via addition of procaspase-9 molecules -> caspase cascade -> apoptosis

66
Q

The positively acting signal proteins can be classified, on the basis of their function, into three major categories…what are they?

A
  1. survival factor - cell survival
  2. mitogens - stimulate cell division
  3. growth factors - stimulate cell growth
67
Q

How does survival factor avoid apoptosis? tissue eg…?

A 
survival factor (released by target cells) -> Bcl2 gene -> Bcl2 protein -> apoptosis blocked
eg. neurons
68
Q

How does mitogen promote cell proliferation? eg?

A

mitogen + receptor -> intracellular signalling pathway -> G1-Cdk and G1/S-Cdk complexes -> phosphorylation of Rb (retinoblastoma protein - ‘brake’) protein -> activate transcription regulator -> cell division
Eg. platelet-derived growth factor (PDGF) in clots & wound healing

69
Q

T or F - Some signals can be mitogenic and growth inducing Eg.?

A

true - PDGF

70
Q

What does myostatin do?

A

inhibits the growth and proliferation of the myoblasts that fuse to form skel- etal muscle cells during mammalian development

BMS241 final exam (5 decks)

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