Lecture 4

Question 1

what are the 3 choices stem cells can make?

Answer 1

1) self renewal
2) differentiation
3) death

Question 2

what are the 3 major steps of the cell cycle?

Answer 2

1) cell growth and chromosome replication
2) chromosome segregation
3) cell division

Question 3

what are the 4 phases of the cell cycle?

Answer 3

1) G1 phase
2) S phase
3) G2 phase
- first 3 steps are interphase
4) mitosis

Question 4

what 3 things happen in the G1 phase?

Answer 4

• cell increases in size
• RNA is produced
• prep for DNA synthesis

Question 5

what 2 things happen in the S phase?

Answer 5

• DNA is synthesised

- chromosomes duplicated

Question 6

what 2 things happen in the G2 phase?

Answer 6

• cell checks fidelity of DNA

- prep for nuclear division

Question 7

what are the 5 phases of mitosis?

Answer 7

1) prophase
2) prometaphase
3) metaphase
4) anaphase
5) telophase

Question 8

what are 3 basic components which regulate the cell cycle?

Answer 8

1) cyclin dependent kinases
2) cyclins
3) CDK inhibitor proteins
(CDK complexes)

Question 9

what are 2 differences about the expression of each cyclin in mammals?

Answer 9

1) they are each limited to a specific cell cycle phase

2) each binds to a specific CDK partner

Question 10

what is the role of cyclin D?

Answer 10

direct link between the extracellular environment and the cell cycle - most growth factors act by directly up-regulating cyclin D expression ie promoting self renewal

Question 11

what phase are cyclin D+E linked with?

Answer 11

G1 phase

Question 12

what phase in cyclin A linked with?

Answer 12

S phase

Question 13

what phase in cyclin B linked with?

Answer 13

Mitosis

Question 14

what is the restriction point?

Answer 14

point of no return the cell is committed to complete the remainder of the cell cycle or exit into G0

Question 15

what does the ink4 family do?

Answer 15

inhibit CDK4 - preventing cyclin binding

Question 16

what does the KIP family do?

Answer 16

CDK inhibitor protein - prevent cyclin-CDK activation

Question 17

what is different between pluripotent stem cell cycles and somatic cell cycles?

Answer 17

in PSCs the G1 phase is shorter and S phase is longer- this is because they don’t have a long restriction point in G1 if any damage is observed they just trigger apoptosis - their turnover of division is fast enough and it avoids any mutations occurring throughout the embryo

• self renewal is maintained in S phase and differentiation is prevented

Question 18

what is G0?

Answer 18

when the cell is in quiescent state. G0 phase is sometimes viewed as an extended G1 phase, where the cell is neither dividing nor preparing to divide.

Question 19

what is the key cell cycle transition point?

Answer 19

G1/S

Question 20

what are cells sensitive to in G1?

Answer 20

different signals

Question 21

when does self renewal control?

Answer 21

S/G2

Question 22

what is Apoptosis?

Answer 22

programmed cell death

Question 23

what can malfunction of apoptosis lead to?

Answer 23

disease

Question 24

what is apoptosis role in stem cells?

Answer 24

too much (tissue atrophy) - problems with regeneration by loss of stem cells  
too little (hyperplasia) - problems with function  - too many stem cells

Question 25

what is the difference between apoptosis and necrosis?

Answer 25

apoptosis is purposeful cell death whereas necrosis is accidental cell death apoptosis = shrinking of cytoplasm and nuclear condensation - mitochondria release death signals necrosis = swelling of cytoplasm - total cell lysis - disintegration of organelles

Question 26

what are 2 things which make a cell decide to commit suicide?

Answer 26

1) withdrawal of positive signals | 2) presence of negative signals

Question 27

what are 2 apoptosis pathways?

Answer 27

1) intrinsic - intracellular proteins - inhibit or promote apoptosis DNA damage 2) extrinsic - signal comes from surrounding cells by death ligands which bind and initiate caspase cascade

Question 28

what are 4 typical features of cancer stem cell cycles?

Answer 28

1) cannot arrest at G0 2) failure to respond appropriately to growth factor signals 3) cells do not have limited replicative life span 4) loss of G1/S restriction point control

Question 29

what are caspases?

Answer 29

family of proteases - molecules which cause apoptosis