w11 txtbk Flashcards

1
Q

cell cycle

A

process where cell duplicates its contents and divides into 2

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2
Q

M phase

A

period of the eukaryotic cell cycle during which the nucleus and cytoplasm divide to produce 2 daughter cells

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3
Q

interphase

A

long period of the cell cycle b/w one mitosis and the next

-includes G1 phase, S phase and G2 phase

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4
Q

S phase

A

s=synthesis

period during euk. cell cycle where DNA is synthesized

-flanked by 2 “gap” phases called g1 and g2 during which the cell continues to grow

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5
Q

g1 phase

A

falls b/w end of cytokinesis and start of DNA synthesis

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6
Q

g2 phase

A

falls b/w the end of DNA synthesis and the beginning of mitosis

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7
Q

what would happen if interphase lasted only long enough for DNA replication

A

the cell wouldn’t have time to double its mass before it divided

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8
Q

cell-cycle control system

A

guarantees that the events of the cell cycle
(DNA rep., mitosis…) occur in a set sequence and that each process finishes before next one starts

-to control this, the system is regulated at certain critical points of the cycle by feedback from the process currently being performed
–cannot be delayed

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9
Q

how is mitosis or cell division delayed

A

if needed, control system employs a set of molecular brakes called checkpoints, to pause the cycle at certain transition points

-this way, it doesn’t trigger next step until cell is properly prepared

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10
Q

late g1 phase

A

control system confirms that the environ. is favorable for proliferation before moving on to replicate DNA

if conditions unfavorable:
-cells can delay entry into cell cycle and can enter specialized resting state called G0

sometimes referred to as start

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11
Q

transition from G2 to M phase

A

control system confirms the DNA is undamaged and fully replicated
-ensuring the cell doesn’t enter mitosis unless dna is intact

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12
Q

transition midway through mitosis

A

cell cycle control machinery confirms the duplicated chromosomes are properly attached to cytoskeletal machine (called mitotic spindle)

-before the spindle pulls the chromosomes apart and segregates them into 2 daughter cells

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13
Q

why is the g1 phase important in animals

A

point in cell cycle where control system is regulated by outside influences
-signals from other cells stimulate cell proliferation when more cells are needed and block it when not needed

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14
Q

explain the different parts of the cell cycle

A

s phase- cell replicates dna

m phase- where mitosis occurs, followed by cytokinesis

g1 and g2- 2 gap phases between S and M phases, when the cell continues to grow and make preparations for the next phase

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15
Q

cell-cycle control system

A

network of regulatory proteins that govern the orderly progression of a eukaryotic cell thru stages of cell division

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16
Q

how does the cell cycle control system govern the cell cycle

A

by cyclically activating and then inactivating the key proteins and protein complexes that initiate or regulate dna rep, mitosis and cytokinesis

this regulation carried out thru the phosphorylation and dephosphorylation of proteins (switching the activity of a protein on and off)

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17
Q

phosphorylation rxns that control cell cycle

A

carried out by protein kinases, while dephosphorylation is performed by a set of protein phosphatases

kinases at the core of the cell-cycle are present in proliferating cells
-activated only when needed
-activity of each occurs in cyclical fashion

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18
Q

cyclin function

A

regulatory protein whose conc. rises and falls at certain times during cycle

-help control progression from one stage of cell cycle to next by binding to cyclin-dependent protein kinases (dks)

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19
Q

cyclin-dependent protein kinase (Cdk)

A

enzyme that when complexed with regulatory cyclin protein can trigger various events in the cell-division cycle by phosphorylating specific target proteins

-the cyclical changes in cyclic concentrations help drive the cyclic assembly and activation of the cyclin - Cdk complexes
-once activated, cyclin-Cdk complexes help trigger cell cycle events (eg entry into S or M phase)

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20
Q

what occurs in transition points throughout cycle

A

control system monitors cell’s internal state and external conditions before allowing cell to continue thru cycle

For example, it allows entry into the cell cycle and initiation of S phase only if environmental conditions are appropriate; it triggers mitosis only after the DNA has been completely replicated; and it initiates chromosome segregation only after the duplicated chromosomes are correctly aligned on the mitotic spindle

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21
Q

how does the control system monitor and slow progress at transition points

A

at start transition in late G1 phase, it uses Cdk inhibitors to keep cells from entering cell cycle

at G2 to M transition, it suppresses activation of M-Cdk by inhibiting the phosphatase required to activate Cdk
-can also delay chromosome segregation in mitosis by inhibiting the activation of APC/C
=prevents degradation of M-cyclin and other
regulators

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22
Q

how do cyclin-Cdk complexes trigger different stages of cell cycle

A

kinase activity of cdk subunit increases at different stages of cycle

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23
Q

g1 phase

A

important time of decision-making for cell
-based on intracellular signals that provide info
about the size of cell and extracellular signals reflecting conditions in the environ,

machinery can either hold cell transiently in G1, direct it to withdraw into a more prolonged nonproliferative state(G0)

or

allow it to prep entry into another cell cycle

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24
Q

if errors occur during dna rep, how does the cell keep from dividing with dna thats incorrectly or incompletely replicated

A

cell control system uses mechanism that can delay entry into M phase

-for cell to progress into mitosis, inhibitory phosphates must be REMOVED by activating protein phosphatase called Cdc25
–if DNA rep stalls, the presence of single-stranded DNA at replication fork triggers DNA damage response

-part of this response includes inhibition of the phosphatase Cdc25, which PREVENTS the removal of the inhibitory phosphatases from M-Cdk

–as a result, M-Cdk remains inactive and M phase delayed until DNA rep is complete and any DNA damage is repaired

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25
Q

the inactivation of M-Cdk prevents what

A

prevents the onset of M phase

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26
Q

sister chromatids

A

copy of chromosome, produced by DNA rep, that still remains bound to other copy

27
Q

cohesins

A

ring shaped SMC protein complex that organizes interphase chromosomes into a long series of large chromatin loops

-special subset of cohesins holds tg sister chromatids after dna has been replicated

29
Q

what occurs after the 2 duplicated chromosomes have condensed?

A

2 complex cytoskeletal machines assemble in sequence to carry out major mechanical processes that occur in M phase

-mitotic spindle carries out nuclear division(mitosis) and in animals cells, the contractile ring divides entire cell into 2 (cytokinesis)

30
Q

mitotic spindle structure and function

A

composed of microtubules and the various proteins that interact with them, including microtubule-associated motor proteins

responsible for pulling duplicated chromosomes apart and allocating one copy of each chromosome to each daughter cell

31
Q

M phase

A

first 5 stages constitute mitosis (prophase, prometaphase, metaphase, anaphase, telophase)

cytokinesis- final stage of M phase

32
Q

what does the phosphorylation of Cdc25 by M-Cdk do?

A

Activates Cdc25, which in turn activates more M-Cdk

-When phosphorylated, Cdc25 becomes activated, which in turn removes the inhibitory phosphates from M-Cdk, thereby activating more M-Cdk

33
Q

centrosome

A

microtubule-organizing center that sits near the nucleus in an animal cell

during cell cycle, this structure duplicates to form the 2 poles of the mitotic spindle

duplication is needed for centrosome to be able to help form the 2 poles of the mitotic spindle, and allows each daughter cell to receive its own centrosome

34
Q

centrosome duplication

A

begins at the same time as dna rep, and the process is triggered by the same Cdks, Cdk- that initiate dna replication

Initially, when the centrosome duplicates, both copies remain together as a single complex on one side of the nucleus

35
Q

aster

A

as mitosis begins, 2 centrosomes separate and each nucleates a radial array of microtubules called aster

the 2 asters move to opposite sides of nucleus to form the 2 poles of mitotic spindle

36
Q

microtubules and dynamic instability

A

continuously polymerize and depolymerize by the addition and loss of their tubulin subunits: individual filaments alternate b/w growing and shrinking –> dynamic instability

new microtubules generated to balance the loss of those that shorten until they disappear

37
Q

at the start of mitosis, why does dynamic instability increase?

A

M-cdk phosphorylates microtubule-associated proteins that influence microtubule staility

as a result, rapidly growing and shrinking microtubules extend in all directions from the 2 centrosomes, and new microtubules sprout from sides of existing microtub.

38
Q

mitotic spindle

A

array of microtubules and associated molecules that form b/w opposite poles of a euk. cell during mitosis and pulls apart duplicated chromosome sets

39
Q

spindle poles

A

centrosome from which microtubules radiate to form mitotic spindle

40
Q

before M phase

A

-cell increases in size
-dna of chromosomes are replicated and centrosome is duplicated

41
Q

prophase

A

duplicated chromosomes(each w/ 2 sister chromatids) condense

-outside nucleus, the mitotic spindle assembles b/w 2 centrosomes, which start moving apart

42
Q

prometaphase

A

starts abruptly with the breakdown of the nuclear envelope

-chromosomes can now attach to spindle microtubules via their kinetochores and undergo active moment

43
Q

metaphase

A

chromosomes are aligned at the equator of spindle, midway b/w spindle poles

-microtubules attach to opposite poles of spindle

44
Q

anaphase

A

sister chromatids synchronously separate and pulled slowly twd spindle pole to which they’re attached

shorter microtubules contribute to chromosome segregation

45
Q

telophase

A

the 2 sets of chromosomes arrive at poles of spindle
-new nuclear envelope reassembles around each set

division of cytoplasm begins with the assembly of contractile ring

46
Q

cytokinesis (animal cell)

A

cytoplasm is divided in 2 by contractile ring of actin and myosin filaments, which pinches cell into 2 daughters, each with one nucleus

47
Q

what triggers the disintegration of the nuclear envelope

A

process triggered by the phosphorylation and consequent disassembly of nuclear pore proteins and the intermediate filament proteins of the nuclear lamina

48
Q

how do sister kinetochores know that they’re attached correctly

A

the attachment to opposite poles (bi-orientation) generates tension on the kinetochores, which are being pulled in opposite directions

this tension signals that they’re attached correctly and ready to be separated

49
Q

how do chromosomes help with the assembly of the mitotic spindle

A

they stabilize and organize microtubules into functional mitotic spindles

50
Q

what event defines the beginning of metaphase

A

when the duplicated chromosomes(attached to mitotic spindle) become aligned at equator of spindle, halfway b/w the 2 spindle poles, forming the metaphase plate

51
Q

whats required to maintain the metaphase spindle

A

continuous balanced addition and loss of tubulin subunits required

when tubulin addition to the ends of microtubules is blocked by the drug colchicine, tubulin loss continues until metaphase spindle disappears

52
Q

how does anaphase begin

A

with the breakage of the remaining cohesin linkages that hold tg the sister chromatids in the duplicated chromosomes

this release allows each chromosome to be pulled twd the spindle pole to which its attached
-the movement segregates the 2 identical sets of chromosomes to opposite ends of the spindle

53
Q

separase function

A

protease that destroys cohesin linkage

54
Q

securin function

A

before anaphase begins, protease held in inactive state by inhibitory protein called securin
-at beginning of anaphase, securin is targeted for destruction by APC/C (same protein that marks M-cyclin for degradation)

once securin has been destroyed, separase is then free to sever the cohesion linkages

55
Q

chromosome movement in anaphase A vs anaphase B

A

A- kinetochore microtubules shorten and the attached chromosomes move POLEWARD
–driving force thought to be provided by the loss of tubublin subunits frm bothe nds of kinetochore microtubules

B- spindle poles move apart, further segregating the 2 sets of chromosomes
–driving forces provided by 2 sets of motor proteins(members of kinesin+dynein) operating on diff types of microtubules

56
Q

kinesin proteins and microtubules

A

act on the overlapping non-kinetochore microtubules, sliding the microtubules from opposite poles past one another at equator of spindle and pushing spindle poles apart

57
Q

dynein proteins and microtubules

A

anchored to the PM, and move along astral microtubules to pull poles apart

58
Q

how does the cell monitor chromosome attachment?

A

makes use of a negative signal

-kinetochores of unattached chromosomes send a “stop” signal to the cell-cycle control systen
–this signal inhibits further progress thru mitosis by blocking the activation of APC/C

w/o active APC/C, sister chromatids remain glued tg
-so no duplicated chromosomes can be pulled apart until every chromosome has been positioned correctly on mitotic spindle

59
Q

how can mitosis be prolonged?

A

absence of APC/C activity also prevents destruction of cyclins, so that Cdks remain active, thus prolonging mitosis

60
Q

what does the spindle assembly checkpoint control

A

the onset of anaphase, as well as the exit from mitosis

61
Q

what happens during the process of telophase

A

nuclear pore proteins and nuclear lamins that were phosphorylated during prometaphase are now DEphosphorylated, which allows them to reassemble and rebuild nuclear envelope and lamina

-once envelope has been reestablished, pore restore the localization of cytosolic and nuclear proteins and condensed chromosomes decondense into their interphase state
–new nuc. has been created, and mitosis is complete
–all that remains is for the cell to complete division

62
Q

how does APC/C trigger onset of anaphase

A

triggering the cleavage of cohesins that hold sister chromatids together