Cellular Reproduction: The Cell Cycle (3)

Question 1

cell cycle

Answer 1

time from one division to the next division

Question 2

how is the cell cycle divided?

Answer 2

2 phases: M phase & interphase

Question 3

interphase

Answer 3

cell growth & metabolism

Question 4

what causes the variation in duration of interphase?

Answer 4

depends on cell type

Question 5

what are the categories that we did cells into in the cell cycle?

Answer 5

1. cells that don’t cycle but enter a permanent arrest stage, once differentiated remain in that state until they die (ex: neurons, muscle cells, RBCs)
2. Cells that normally don’t divide but can be induced (ex: liver, lymphocytes)
3. Cells that divide regularly (ex: epithelial cells)

Question 6

why do RBCs lack a nucleus?

Answer 6

no longer necessary since they will no longer be dividing

Question 7

what controls cell division?

Answer 7

cytoplasmic factors

Question 8

what was the experiment to find what controls the cell cycle?

Answer 8

fused mitotic & interphase cells

interphase cells in G1 had premature condensed c’some & attempted M phase (the non mitotic cell)

concluded that there is a factor in the mitotic cell that directs cells to undergo mitosis

Question 9

what controls the cell cycle at the G2/M transition?

Answer 9

maturation promoting factor

entry into mitosis requires this PRO complex

Question 10

what is MPF?

Answer 10

complex of 2 PROs:
cyclin b: regulates cdK1 activity, levels rise & fall through the cell cycle
Cdk1: kinase added a phosphate tot other PROs, modifying the target’s PROs activity (cyclin dependent kinase)

Question 11

when is there first an increase in cyclin b?

Answer 11

G2

Question 12

when does cyclin b peak? and when does it drop?

Answer 12

M phase & at the end of M phase

Question 13

what is the role of MPF?

Answer 13

phosphorylates & activates PROs of mitosis

Question 14

when are cyclins not produced?

Answer 14

G0

Question 15

What are some MPF functions?

Answer 15

activates lamin PROs, causing the nuclear envelope to break (dissociates PRO from membrane)

alters DNA bound PROs (histones) causing DNA to condense. During Prophase enabling c’some to travel to poles

activates PROs of the mitotic spindle in pro prometaphase

Question 16

Wee1 PRO & what happens when the mutant lacks it

Answer 16

inhibitor of MPF

results in early cell division (enters too early), smaller daughter cells than what they should be

Question 17

Cdc25 PRO & what happens when the mutant lacks it

Answer 17

activates MPF

division fails too occur, large cell

Question 18

how does cdc25 activate cdk?

Answer 18

Removes phosphate form Tyr15 activating cdk

Question 19

what inhibits MPF activity?

Answer 19

wee1 adds phosphate to Try 15

Question 20

CAK

Answer 20

cyclin activating kinase

adds P to Thr161, when removed mitosis is terminated

activates Cdk1

Question 21

What happens when P is removed from Thr161?

Answer 21

cyclin detaches & degraded, ends mitosis

Question 22

what activates Cdk1?

Answer 22

CAK adds P on Thr161

once removed mitosis ends

Question 23

what inactivates Cdk1?

Answer 23

wee1 phosphate on Tyr15

Question 24

how is cyclin action turned off?

Answer 24

activation of ubiquitin ligase

Question 25

ubiquitin ligase

Answer 25

terminates MPF activity

Attaches ubiquitin to cyclin tagging it for destruction by causing proteolysis

Question 26

What does MPF phosphorylate?

Answer 26

lamin
histones
microtubules
ubiquitin ligase

Question 27

When are cyclins & cdk1 low?

Answer 27

G1

Question 28

proteasome

Answer 28

proteolysis of cyclin terminating MPF activity

Question 29

What is necessary to work at G0 to have successful mitosis?

Answer 29

if wee1 isn’t working the cells go on too soon & end up small

Question 30

What are the MPF checkpoints & end do they occur?

Answer 30

Metaphase checkpoint:
o M phase
o Chromosomes aligned?

Start or restriction checkpoint:
o End of G1
o Cell decides whether to continue or not Cell big enough? Envr okay? DNA okay?

G2 checkpoint:
o G2
o DNA intact post replication?
Will not attempt division if DNA is damaged

MPF checkpoint:
o End of G2
o DNA replicated? Cell big enough? Does it have enough stuff?

Question 31

What is the result of the DNA damage checkpoint in G1 not functioning properly?

Answer 31

Ataxia-telangiectasia (AT)

PROs involved in DNA repair fail indivs with AT

prone to cancer: 
     Ionizing radiation (ATM PRO) - breaks DNA 
     Ultraviolet radiation (ATR PRO)

Question 32

What are the steps in the checkpoint if there is DNA damage?

Answer 32

1. ATM detects break in DNA in G1
2. ATM phosphorylates Chk2 activating it
3. Chk2 phosphorylates p53
4. Phosphorylated p53 activates gene p21 (gene is synthesized)
5. P21 PRO binds to Cdk (inhibition)
   cell prevented from entering S phase until DNA is repaired

Question 33

ATM PRO role

Answer 33

detects break in DNA in G1

Question 34

Chk2

Answer 34

kinase

phosphorylates p53 in cell damage checkpoint

Question 35

p53 role

Answer 35

when phosphorylated, turns on p21 gene causing its synthesis

Question 36

p21

Answer 36

gene synthesized when there is damage in DNA, PRO inhibits Cdk

Question 37

50% of human tumor cells have mutations in which gene?

Answer 37

p53

Question 38

what are the 3 components of a checkpoint?

Answer 38

1. Sensor –> is DNA damaged? (ex: ATM/ATR PROs)
2. Transducer: create a signal, enables the cell to work in a multi-step fashion, diff controls systems interact (ex: Cdc25, p53, MPF PROs)
3. Effector: change key enzyme action/PRO (ex: P21, phosphorylated lamins, histones, ubiquitin etc.)

Question 39

What is the effector in then DNA damage checkpoint?

Answer 39

P21

Question 40

What are the checkpoints in the cell cycle?

Answer 40

1. Progression from G2 to M by the MPF
2. Checkpoints for DNA damage in G2 + G1 (before & after rep) –> cell cycle halts allowing time for repair
3. Spindle checkpoint in M phase