Cell Division and Cell Death Flashcards
How is cell division controlled
Cell Cycle
What powers cell cycle
Cyclin- dependen kinase (CDKs)
what regulates CDKs
cyclins
Cell cycle checkpoints
End of G1, During G2 and End of M
What happens if the cel fails the cell cycle checkpoints
cell is arrested
Checkpoint G1
restriction point
check for cell size and favourable environment conditions, checks for DNA damage
Checkpoint G2
check for damage or unduplicated DNA, checks for unduplicated centrosomes
Checkpoint M
checks that chromosomes are attached to mitotic spindle
What can uncontrolled cell division lead to
Tumours, identically defective daughter cells
Chromosome condensation
- DNA tightly packed into nucleosomes
- Prior to mitosis they become supercoiled
- then becomes inaccessible to proteins involved in replication
Chromosome segregation
- mediated by mitotic spindle
- condensed chromosomes attach to microtubules which radiate from the two centrosomes
Phases of mitosis
Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase
- Interphase
During S phase, the nucleus replicates its DNA and centrosomes
- Prophase
= condenses into chromosome
- chromosome contains sister chromatid
- centrosomes move to opposite poles
- Prometaphase
nuclear envelope breaks down
- kinetochore microtubules appear and connect to kinetochores to the poles
- Metaphase
centrosomes align in a plane at equator
- Anaphase
paired sister chromatids separate
- new daughter chromosomes begin to move toward the poles
- Telophase
daughter chromosomes reach poles
- nuclear envelopes and nucleoli reform
- cytokinesis
- repeat
Acto- myosin ring
contraction drives cytokinesis
Types of cell death
Apoptosis
Autophagic cell death
Necroptosis
Necrosis
Necrosis
- caused by cell damaging agents
- no energy required
- cell swelling and lysis
- generates inflammatory response
apoptosis
- cell suicide
- cell contents are not released
- DNA and proteins broken down
- Dying cells engulfed by phagocytic cells
- no inflammatory response
Apoptosis morphology
- cell condensation
- membrane bedding
- nuclear shrinkage
- chromatin condensation and fragmentation
- formation of apoptosis bodies
Functions of Apoptosis
- regulating cell number by balancing cell division
- developmental process
- removal of phcagogenic cells
Two distinct classes of caspases
Initiator
Executor
Initiator caspases
activated by pro-apoptotic stimuli
- cleave and activate executor caspases
8,9,10
Executor caspases
activated by inhibitor caspases
- cleave a variety of target proteins resulting in execution of apoptosis
3,6,7
Role of mitochondria in apoptosis
Opening of pores in mitochondria outer membrane tiggers cytochrome C release and caspase activation
Role of Bcl-2 in apoptosis
prevents the formation of pores in the mitochondrial out membrane
- the cell must over come this to activate programmed cell death pathways
