Lecture 4 Flashcards
what are the 3 choices stem cells can make?
1) self renewal
2) differentiation
3) death
what are the 3 major steps of the cell cycle?
1) cell growth and chromosome replication
2) chromosome segregation
3) cell division
what are the 4 phases of the cell cycle?
1) G1 phase
2) S phase
3) G2 phase
- first 3 steps are interphase
4) mitosis
what 3 things happen in the G1 phase?
- cell increases in size
- RNA is produced
- prep for DNA synthesis
what 2 things happen in the S phase?
- DNA is synthesised
- chromosomes duplicated
what 2 things happen in the G2 phase?
- cell checks fidelity of DNA
- prep for nuclear division
what are the 5 phases of mitosis?
1) prophase
2) prometaphase
3) metaphase
4) anaphase
5) telophase
what are 3 basic components which regulate the cell cycle?
1) cyclin dependent kinases
2) cyclins
3) CDK inhibitor proteins
(CDK complexes)
what are 2 differences about the expression of each cyclin in mammals?
1) they are each limited to a specific cell cycle phase
2) each binds to a specific CDK partner
what is the role of cyclin D?
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
what phase are cyclin D+E linked with?
G1 phase
what phase in cyclin A linked with?
S phase
what phase in cyclin B linked with?
Mitosis
what is the restriction point?
point of no return the cell is committed to complete the remainder of the cell cycle or exit into G0
what does the ink4 family do?
inhibit CDK4 - preventing cyclin binding
what does the KIP family do?
CDK inhibitor protein - prevent cyclin-CDK activation
what is different between pluripotent stem cell cycles and somatic cell cycles?
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
what is G0?
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.
what is the key cell cycle transition point?
G1/S
what are cells sensitive to in G1?
different signals
when does self renewal control?
S/G2
what is Apoptosis?
programmed cell death
what can malfunction of apoptosis lead to?
disease
what is apoptosis role in stem cells?
too much (tissue atrophy) - problems with regeneration by loss of stem cells too little (hyperplasia) - problems with function - too many stem cells
what is the difference between apoptosis and necrosis?
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
what are 2 things which make a cell decide to commit suicide?
1) withdrawal of positive signals
2) presence of negative signals
what are 2 apoptosis pathways?
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
what are 4 typical features of cancer stem cell cycles?
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
what are caspases?
family of proteases - molecules which cause apoptosis
