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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
describe S phase
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
describe G2 if DNA is not replicated correctly phase
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
how is M-Cdk activated
when Cdc25 removes the inhibitory phosphates
28
active M-Cdk acts via ___ ____ loop, activating more ____ which activates more ____
active M-Cdk acts via positive feedback loop, activating more Cdc25 which activates more M-Cdk
29
describe entry into M phase (2)
- 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
what shifts a cell from G2 into Mitosis
massive increase in active M-Cdk
31
what are cohesin
large protein ring that wraps around two sister chromatids, holding them together so they wont separate until anaphase
32
what are condensins
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
what happens in prophase
chromosomes condense and move to opposite sides of nucleus / formation of mitotic spindle -cohesins and condensins
32
M-Cdk phosphorylates NPCs and _____ triggering what
NPCs and nuclear lamins, triggering disassembly of nuclear lamina and leading to the breakdown of nuclear envelope
33
when is the nuclear envelope broken down and when is it reassembled
broken down - prophase (proteins phosphorylated) reassembled - telophase (proteins dephosphorylated)
34
the cytoskeleton filaments that form the mitotic spindle are ___ and those involved in the contractile ring in cytokinesis are ____
microtubules and actin (microfilaments)
34
what is the mitotic spindle in and what is it
in mitosis = is microtubules and kinesin/dynein motor proteins that separate chromosomes
35
what is the contractile ring in and what is it
in cytokinesis = is made of actin filaments and myosin motor proteins which separates 2 daughter cells
36
steps of the centrosome cycle (3)
- 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
what is an aster
short microtubules that extend out from the centrosome towards cortex
38
describe metaphase
-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
does the + or - end of MT bind to kinetochore
+ end
40
what generates the tension in metaphase
kinetochore MTs from each pole will attach to opposing kinetochores on sister chromatids
41
describe what happens in anaphase (3) and what is it triggered by
-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
describe APC in anaphase
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
kinesins are in between the ___ while dyneins are anchored to ___ ____
in between MTs while dyneins are anchored to cell cortex
44
what causes spindle poles in anaphase to push apart
kinesin and dynein push MT in opposite directions, causing spindle poles apart
45
what happens in telophase
dephosphorylation of lamins triggers reformation of nuclear envelope
46
3 types of spindle microtubules
kinetochore - interact with kinetochores interpolar -interact in middle astral - extend toward cell cortex
47
compare chromosomes being pulled apart vs poles being pushed apart in anaphase
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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