Cell Division Flashcards
What controls the cell cycle
cyclin dependant kinases, there activity increases during mitosis
how is mitosis regulated
by phosphorylation/dephopshorylation
Ubiquitination
an enzymatic post-translational modification in which a ubiquitin protein is attached to a substrate protein. This process most commonly binds the last amino acid of ubiquitin (glycine 76) to a lysine residue on the substrate
Proteasome
has two important areas:
the CP region which is the core
the RP region which is where the Ub is recognised
- this is then fed through the core where is has the capacity to break it up and the remnants are secreted out the end
What are the first two checkpoints in the G1 phase
- checks for damaged dNA
2. unfavourable extracellular environment
what is the checkpoint in the S phase
damaged or incompletely replicated DNA
what is the checkpoint in the G2 phase
damaged or incompletely replicated DNA
what is the checkpoint phase in the M phase
chromosome improperly attached to mitotic spindle
Cyclin dependent kinase inhibitors
Transcription of inhibitors can be induced if conditions are not right for cell division
what is the R point
G1/S transition
also known as quiescence
DNA damage
• Response depends on stage of cell cycle • p53- directs transcription of cdk-inhibitors • CHK2 is activated- inhibits cdc25
what are the stages of mitosis
Prophase Prometaphase metaphase anaphase telephone cytokinesis
Metaphase
- Mitosis cannot proceed until chromosomes are properly attached and under tension
- Spindle checkpoint
Cohesion complex
Holds sister chromatids together
Defects in cohesion can cause disease
- Roberts Syndrome
- Very rare
- Nature Genetics 37:468- 70
Defects at spindle checkpoint can cause
aneuploidy
Cytokinesis
remaining inter polar miscrotubules form central spindle
contractile ring of actin and myosin filaments in cleavage furrow
A cyclin CDK complex is activated by what
activating protein phosphatase which removes a phosphate
what is wee1 mutant
it is a form of inhibitory kinase where as CDC 25 is an activating phosphatase
what are the two complexes that control events in ell division
active S-Cdk which ha a bound S-cyclin between G1 and S phase
active M-Cdk with bound M-cyclin between the G2 and M phase
tell me about the pathway of ubiquitylation
it ultimately leads to the destruction of cyclin resulting in an inactive Cdk
- Ub binds to E1 which is a Ub activating enzyme, with the consumption of ATP
- This then transfers the Ub to E2 a Ub conjugating enzyme
- this then binds to E3 a Ub ligase which is already bound to the substrate
- the Ub then transfers on to the substrate
- this cycle can repeat until there are multiple but it sends a DESTROY signal
in the G1 phase what ensures only one cycle happens
the pre-replicative complex is bound to the origin od replication site with the Cdc6 molecule bound which is an inhibitor
- s-cdk then triggers the s phase so the cdc6 molecule unbinds along with other proteins and is degraded by phosphorylation to prevent it binding back
- this allows the assembly of the replication fork to begin
what molecule can lead to inhibition of transcription of there is DNA damage
p53 which directs transcription of cdk inhibitors
CHK2 can also be activated which inhibits cdc25
what is the action of the anaphase complex
for anaphase to commence the inhibitory protein securin (which is bound to the inactive proteolytic enzyme separase) has too be removed by active APC
- this leads to the ubiquination and degradation of secruin
- these means the now active separase can go on to cleave and dissociate cohesins
