Cell Cycle (Dr. Pfeffer)

Question 1

What is the basis of cell cycle control?

Answer 1

cyclically activated protein kinases

Question 2

What is cell cycle control?

Answer 2

a series of counter balances…

• synthesis and degrdation
• phosphorylation and dephosphorylation

Question 3

Who were the first to characterize cell cycle regulation in different organisms? (this was in red on the ppt…)

Answer 3

Hartwell, Hunt and Nurse (in the ’70s and ’80s)

Question 4

Microtubule and microfilament disruption will cause the cell cycle to arrest at ___ phase?

Answer 4

M

Question 5

If DNA replication is disrupted at what phase will the cell cycle arrest?

Answer 5

S

Question 6

What agents disrupt microtubule function?

Answer 6

vincristine
vinblastine
taxol
colchicine

*arrests cell at M phase

Question 7

What agents disrupt microfilament structure?

Answer 7

cytochalastin

*arrests cell late in M phase bc this blocks cytokinesis

Question 8

What is the longest phase of the cell cycle?

Answer 8

G1

Question 9

What phases of the cell cycle is the chromosome state 4n?

Answer 9

Late S, G2, early M

Question 10

When will stable cells begin to divide?

Answer 10

When they receive a signal

Question 11

When will permanent cells begin to divide?

Answer 11

they don’t divide (for the most part)

Question 12

______ function to ensure correct cycling.

Answer 12

Checkpoints

Question 13

What is “checked” at the G1 checkpoint?

Answer 13

Is the cell big enough?
Is the enviro right?
Is DNA damaged?

Question 14

What is “checked” at the G2 checkpoint?

Answer 14

Is all the DNA replicated?

Is the cell big enough?

Question 15

Describe the Rao and Johnson nuclear fusion experiments? (4 tests)

Answer 15

Nuclei in various phases of the cell cycle we combined to see if the different phases had factors assc with it that influence cells to enter into certain parts of the cell cycle

1. S + G1 –> S
   (S cell “releases” factors induce G1 to proceed into S)
2. S + G2 –> nothing
   (G2 is resistant to factors from S phase cell)
3. G1 + G2 –> nothing
   (G1 and G2 do not have factors that influence each other)
4. interphase + M –> M
   (M phase has factors that induce all other cells to enter into M phase)

Question 16

What happens to cells that are not read to transit into the S phase from G1?

Answer 16

go into G0 phase

Question 17

What happens to cells in G1 that are under stress?

Answer 17

apoptosis

Question 18

What happens in S phase?

Answer 18

DNA replication and sythsis of DNA pol and histones

Question 19

What happens in G2 phase?

Answer 19

synthesis of proteins needed for mitosis

Question 20

What happens in M phase?

Answer 20

mitosis

Question 21

What is the Hayflick number?

Answer 21

proliferation potential od cells (as we age, out hayflick number decreases (inverse relationship))

Question 22

What is progeria?

Answer 22

pre-mature aging disease

Question 23

What is senescence?

Answer 23

cells are alive but are not dividing (occurs when cells have reached their proliferation potential

Question 24

The time spent in ____ phase is highly variable (meaning in many different studies, researchers found wide ranges of time spent in this phase relative to other phases)

Answer 24

G1

Question 25

What is MPF?

Answer 25

maturation promoting factor or cyclin B + Cdc2 kinase

Question 26

What happens to a cell arrested in G2 and then has MPF added to it?

Answer 26

it enters in M phase

Question 27

What happens to a cell arrested in G2 and then has progesterone added to it?

Answer 27

it enters into M phase

Question 28

MPF promotes ____ in somatic cells

Answer 28

mitosis

Question 29

MPF activity oscillates in assc with _____

Answer 29

cyclin conc

Question 30

T or F: MPF concentration oscillates throughout the cell cycle

Answer 30

F: the conc on MPF is constant

Question 31

Why does cell division not constantly occurring?

Answer 31

cyclin levels are not constant. M phase occurs only when cyclin is present

Question 32

MPF =

Answer 32

cyclin B + Cdc2 kinase

Question 33

WIll a larger or smaller yeast "bud" enter into S phase faster?

Answer 33

bigger bud bc the smaller one must grow in order to move past the G1 checkpoint

Question 34

What effect does Wee1 gene have on MPF?

Answer 34

inhibits it

Question 35

What effects does Cdc25 have on MPF?

Answer 35

activates it

Question 36

What is the result of excess Cdc25 and deficient Wee1?

Answer 36

small cells that spend less time in G2

Question 37

What is the result of deficient Cdc25 and excess Wee1?

Answer 37

elongated cells that spend more time in G2

Question 38

Describe active MPF.

Answer 38

Y15 is NOT phosphorylates and T161 is phosphorylated. This allows for the substrate binding site to be exposed

Question 39

Is completely dephosphorylated MPF active or inactive?

Answer 39

inactive

Question 40

What is p27? What is its role in the cell cycle?

Answer 40

it bind to ACTIVE cyclin-Cdk complex (MPF) to inactivate it

Question 41

Mitotic Cdk is made during __ phase but kept inactive until ___ phase

Answer 41

G2; M

Question 42

What is the role of SCF?

Answer 42

when active, it phosphorylates p27 (Cdk inhibitor) to tag it for ubiquination/degradation by proteosome *regulator of proteolysis

Question 43

What is the role of APC? (anaphase promoting complex)

Answer 43

when APC is bound by Cdc20 it is active --> | active APC tags Cyclin M-Cdk complex for ubiquination/degradation

Question 44

If you have defective or deficient SCF, what is the effect in the cell cycle?

Answer 44

Cdk is inhibited more frequently bc there is more p27 (or Cdk inhibitor)

Question 45

How does SCF have to be altered to lead to unregulated cell proliferation?

Answer 45

if SCF is constitutively active, Cdk inhibitor (p27) is constantly being degraded --> Cdks are constantly active --> cell cycle on ***this was not from the notes, this is me trying to come up with things they may make up come up with... so I'm probably wrong somewhere in my reasoning

Question 46

How does APC have to be altered to lead to unregulated cell proliferation?

Answer 46

if APC mutated so that it can cannot be activated by Cdk20 binding --> Cdk-Cyclin M is not degraded --> can turn on cell cycle If active APC cannot bind Cdk-Cyclin M complex --> cell cycle on bc Cdk-Cyclin M is not degraded ***this was not from the notes, this is me trying to come up with things they may make up come up with... so I'm probably wrong somewhere in my reasoning

Question 47

At what phase of mitosis in APC active? inactive?

Answer 47

active during late anaphase | inactive during prophase (When cyclin B is made)

Question 48

When in the cell cycle is MPF active?

Answer 48

G2 checkpoint to induce M phase

Question 49

When S cyclin is present what occurs?

Answer 49

cell proceeds into S phase

Question 50

When M cyclin is present what occurs?

Answer 50

cell proceeds into M phase

Question 51

How are cyclins regulated?

Answer 51

phosphorylation, inhibitors (p53, p27, etc), conc of cyclins (Tx or proteolysis=APC)