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BIOL 2202 CMB Final > Chapter 18 > Flashcards

Chapter 18 Flashcards

1
Q

mitosis divides ____ while ____ divides cytoplasm

A

mitosis divides chromosomes
cytokinesis divides cytoplasm

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2
Q

to reproduce all cells go thru a series of events called ___ ____
what does it do and what is produced?

A

cell cycle

cells grow, duplicate, segregate and it produces 2 genetically identical daughter cells

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3
Q

is the length of the cell cycle the same for all cells?

A

NO, it varies
mostly comes from variation in G1 phase

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4
Q

what are the interphase sub-phases and what do each do

A

G1 = day to day activities/ growth
S phase =synthesis / DNA replication
G2 = prepares for division

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5
Q

what makes up the M phase

A

mitosis then cytokinesis

mitosis = PMAT

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6
Q

describe G0

A

happens in G1 = some cells will exit the cell cycle, temporarily or permanently

permanently - terminally differentiated/highly specialized cells that do not divide

temporarily - some cells don’t normally divide but can when given a stimulus

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7
Q

what is the cell cycle control system

A

3 main checkpoints

  1. before entering S phase (G1/S-Cdk /Rb, p53)
  2. before entering M phase (M-Cdk/ Cdc25)
  3. in anaphase (APC)
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8
Q

what are the 2 most important protein families in cell cycle control and describe

A
  1. Cyclins
    -regulatory proteins that bind to Cdks
    -no enzymatic activity
    - !concentrations! fluctuate in cyclic manner
  2. Cyclin-dependent protein kinases (Cdks)
    -cyclins bind to them
    -enzymatic activity by cyclin binding
    -activated by phosphorylation/dephosphorylation
    - concentrations remain same !activity! fluctuates
    - are kinases so phosphorylate other proteins
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9
Q

the 4 main cyclin-Cdk complexes

A

G1-Cdk
G1-S-Cdk (start)
S-Cdk (entry into S)
M-Cdk (entry into M)

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10
Q

when will Cdk activity be the highest ?

A

when cyclins levels are high

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11
Q

what does an increase in cyclin vs a decrease mean

A

increase = increased transcription of cyclin genes
decreased = targeted destruction (ubiquitin)

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12
Q

Cdks are ____ when the cyclins are degraded

A

inactivated

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13
Q

activation of Cdks depends on …. (3)

A
  1. phosphorylation of Cdk
  2. binding of Cdk to cyclin partner to produce cyclin-Cdk complex
  3. activation of cyclin-Cdk complex by dephosphorylation (one P remains)
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14
Q

activity of cyclin-Cdk complexes can be decreased by …. (3)

A
  1. degradation of cyclins
  2. inhibitory proteins
  3. inhibitors
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15
Q

describe Wee1

A

a kinase
= inactivates cyclin-Cdk by ADDING 2 inhibitory phosphates

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16
Q

describe Cdc25

A

a phosphatase = activates cyclin-Cdk by REMOVING the 2 inhibitory phosphates

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17
Q

what are the 2 inhibitors in cell cycle control

A

can regulate cyclin-Cdk activity
-p27 and p21

=physically blocks it from interacting with proteins / cyclin-Cdk cant phosphorylate
ex. p27 prevents entry into S phase

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18
Q

Cyclin-Cdk complexes are responsible for ____

A

phosphorylating target proteins

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19
Q

cyclin-Cdk activity is regulated by _____ & _____

A

phosphorylation and dephosphorylation

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20
Q

describe G1

A

day to day activities
-can go into S phase, pause in G1 or enter G0

-at start of G1 all Cdks are INACTIVATED

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21
Q

describe Rb and Mitogens in G1

A

Rb (retinoblastoma protein) = inhibits TFs (E2Fs)

  1. Mitogen once bound to cell surface receptors turns on G1/S-Cdk via intracellular signaling, which phosphorylates Rb, inactivating it
  2. now that Rb is inactive transcription can occur (stimulate cell proliferation)and cell can enter S phase

*without mitogens Rb inhibits transcription / stays in G1 (halting cell division)

22
Q

what two things can halt progression into S phase

A

Rb and p53&p21

23
Q

DNA damage results in ___ and describe what is produces

A

activation of p53 protein (TF)

p21 is produced
-p21 = Cdk inhibitor that binds to G1/S-Cdk and S-Cdk and INACTIVATES them which causes cell to pause in G1 and repair

*can also halt G2->M

24
Q

what does S-Cdk do

A

S-Cdk initiates DNA replication and prevents re-replication

25
Q

describe S phase

A

G1
1. ORC recruits Cdc6
2. Cdc6 rises early in G1 and helps load helicase at Ori
3. S-Cdk is assembled and activated at end of G1

S PHASE
4. S-Cdk activates helicase and other replication enzymes thru phosphorylation
5. S-Cdk “pulls the trigger” that initiates DNA synthesis
6. S-Cdk blocks re-replication by inactivating Cdc6 (marks for degradation)

26
Q

describe G2 if DNA is not replicated correctly phase

A

if DNA is not replicated correctly or cell too big must delay entry into M phase

so inhibit Cdc25

-Cdc25 is inactivated so that M-Cdk remains inactive and cell cycle halts in G2 phase until ready

27
Q

how is M-Cdk activated

A

when Cdc25 removes the inhibitory phosphates

28
Q

active M-Cdk acts via ___ ____ loop, activating more ____ which activates more ____

A

active M-Cdk acts via positive feedback loop, activating more Cdc25 which activates more M-Cdk

29
Q

describe entry into M phase (2)

A
  • active M-Cdk activates Cdc25 and shuts down Wee1 kinase
    -inactive M-Cdk are stockpiled during G2 but are not activated till end of G2 and once activated they drive entry into M phase
30
Q

what shifts a cell from G2 into Mitosis

A

massive increase in active M-Cdk

31
Q

what are cohesin

A

large protein ring that wraps around two sister chromatids, holding them together so they wont separate until anaphase

32
Q

what are condensins

A

bind to chromatin to help it coil into mitotic chromosomes
-M-Cdk phosphorylates them to activate them
-trigger compaction of chromatin into condensed mitotic chromosomes

32
Q

what happens in prophase

A

chromosomes condense and move to opposite sides of nucleus / formation of mitotic spindle

-cohesins and condensins

32
Q

M-Cdk phosphorylates NPCs and _____ triggering what

A

NPCs and nuclear lamins, triggering disassembly of nuclear lamina and leading to the breakdown of nuclear envelope

33
Q

when is the nuclear envelope broken down and when is it reassembled

A

broken down - prophase (proteins phosphorylated)
reassembled - telophase (proteins dephosphorylated)

34
Q

the cytoskeleton filaments that form the mitotic spindle are ___ and those involved in the contractile ring in cytokinesis are ____

A

microtubules and actin (microfilaments)

34
Q

what is the mitotic spindle in and what is it

A

in mitosis = is microtubules and kinesin/dynein motor proteins that separate chromosomes

35
Q

what is the contractile ring in and what is it

A

in cytokinesis = is made of actin filaments and myosin motor proteins which separates 2 daughter cells

36
Q

steps of the centrosome cycle (3)

A
  • centrosome is duplicated in S phase so that each centrosome can form one pole of the mitotic spindle
  • happens in S phase to G2
  • triggered by G1/S-Cdk and S-Cdk
37
Q

what is an aster

A

short microtubules that extend out from the centrosome towards cortex

38
Q

describe metaphase

A

-sister chromatids become attached to MT by their kinetochores
-chromosomes are moved and aligned in middle
-in middle, at metaphase plate, sister chromatids are constantly pulled on by MTs at each pole creating tension

39
Q

does the + or - end of MT bind to kinetochore

A

+ end

40
Q

what generates the tension in metaphase

A

kinetochore MTs from each pole will attach to opposing kinetochores on sister chromatids

41
Q

describe what happens in anaphase (3) and what is it triggered by

A

-sudden synchronous splitting apart of centromeres
-separation of sister chromatids to form daughter chromosomes
-movement of daughter chromosomes toward opposite poles of the cell (loss of tubulin)

triggered by APC

42
Q

describe APC in anaphase

A

Anaphase promoting complex
=promotes destruction of cohesin proteins

-securin is normally bound to separase
-APC marks securin with ubiquitin and destroys it
-separase is no longer bound to securin and so is activated
- active separase cleaves cohesins and allows for separation of sister chromatids

43
Q

kinesins are in between the ___ while dyneins are anchored to ___ ____

A

in between MTs while dyneins are anchored to cell cortex

44
Q

what causes spindle poles in anaphase to push apart

A

kinesin and dynein push MT in opposite directions, causing spindle poles apart

45
Q

what happens in telophase

A

dephosphorylation of lamins triggers reformation of nuclear envelope

46
Q

3 types of spindle microtubules

A

kinetochore - interact with kinetochores
interpolar -interact in middle
astral - extend toward cell cortex

47
Q

compare chromosomes being pulled apart vs poles being pushed apart in anaphase

A

chromosomes being pulled apart = kinetochore MTs shorten and so chromosomes are pulled to opposite sides

poles being pushed apart = interpolar MTS slide and pull spindle poles apart *kinesin and dynein push in opposite directions

BIOL 2202 CMB Final (4 decks)

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