theme 3-CB 16 Cell cycle and cell division Flashcards
define the cell cycle
The cycle of duplication and
division (co-ordinated) that is undertaken to replicate the
cell and its contents
Why is the cell cycle important:
Fundamental to growth and
development of the organism
What is the relationship between the cell cycle and cell devision
cell division in M phase of the cell cycle
What are the main events of the cell cycle:
1) M phase
2) G1 phase
3) S phase
4) G2 phase
Describe G1 phase during interpase:
gap
Describe S phase during interpase:
DNA replication
Describe G2 phase during interpase:
gap
What happens in M phase in the cell cycle:
mitosis and cytokinese
what happens in prophase?
- chromosome condensation
- formation of spindle apparatus
- nuclear envelope breaks down
- spindle attaches to centromeres (kinetochore)
What happens in metaphase?
-chromosomes align at equator (using motor protiens and microtubules)
What happens in anaphase?
-sister chromatids pulled apart
What happens in telophase?
- nuclear envelope reforms
- cytokinesis (contractile ring (actin and myosin filaments , cyoplasm divides)
- chromosomes unravel
What are proteasomes?
protein complexes which degrade unneeded or damaged proteins by proteolysis
What do activated cyclin dependent kinases?
turns biochemical switches that act in a sequence on (by phosphorylation) and off (by dephosphorylation) which allows synthesis of new components as well as partition and division process to be regulated.
What do activated cyclin dependent kinases?
turns biochemical switches that act in a sequence on (by phosphorylation) and off (by dephosphorylation) which allows synthesis of new components as well as partition and division process to be regulated.
How are cyclin-dependent kinases activated?
mitogens causes accumulation of a particular cyclin at the appropriate time during the cell cycle.
1) cyclin binds to cdk= cyclin-cdk complex
2) protein kinases phosphorylate complex, one phosphate is activating and one in inhibiting, the inhibiting phosphate is expressed.
3) Activating protein phosphatase desphosphorylates complex, removing inhibiting phosphate= activated cyclin-cdk complex.
How is a particular cyclin-cdk switched off?
1) cyclin is ubiquitylated by anaphase promoting complex (APC)
2) Marks it for destruction
3) proteosomes degrade cyclin, breaking up complex
How is a particular cyclin-cdk switched off?
1) cyclin is ubiquitylated by anaphase promoting complex (APC)
2) Marks it for destruction
3) proteosomes degrade cyclin, breaking up complex
How do cells move through the cell cycle?
through a series of checkpoints, at each checkpoint, a particular cdk must be activated then deactivated through phosphorylation and dephosphorylation reactions.
What stops the cell cycle? +e.g.
through the synthesis of cdk inhibitor proteins, like p21, that bind to cyclin-cdk complexes and inactivate them.
Describe what would occur after DNA damage is noticed by the cell?
1) protein kinases would be activated and phosphorylate p53, a protein being synthesised by the cell all the time
2) The phosphorylation of p53 makes it stable (so isn’t degraded in proteosomes like it normally is) and activated.
3) activated p53 binds to regulatory region = transcription of p21 gene
4) p21 is synthesised
5) p21 binds to active cyclin-cdk complex = stops its function
What 2 things can occur after p21 has bound to cyclin-cdk complex?
1) DNA repaired, p21 releases complex
2) DNA unable to be repaired= cell apoptosis
What percentage of cancers are caused by a mutation in p53 gene?
Why does it cause cancer?
50%
mutation means DNA doesn’t have time to be repaired if other mutations occur, and cell apoptosis cannot occur= uncontrolled cell growth
