Cell Division

Question 1

What controls the cell cycle

Answer 1

cyclin dependant kinases, there activity increases during mitosis

Question 2

how is mitosis regulated

Answer 2

by phosphorylation/dephopshorylation

Question 3

Ubiquitination

Answer 3

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

Question 4

Proteasome

Answer 4

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

Question 5

What are the first two checkpoints in the G1 phase

Answer 5

1. checks for damaged dNA

2. unfavourable extracellular environment

Question 6

what is the checkpoint in the S phase

Answer 6

damaged or incompletely replicated DNA

Question 7

what is the checkpoint in the G2 phase

Answer 7

damaged or incompletely replicated DNA

Question 8

what is the checkpoint phase in the M phase

Answer 8

chromosome improperly attached to mitotic spindle

Question 9

Cyclin dependent kinase inhibitors

Answer 9

Transcription of inhibitors can be induced if conditions are not right for cell division

Question 10

what is the R point

Answer 10

G1/S transition

also known as quiescence

Question 11

DNA damage

Answer 11

• Response depends on stage of cell cycle • p53- directs transcription of cdk-inhibitors • CHK2 is activated- inhibits cdc25

Question 12

what are the stages of mitosis

Answer 12

Prophase 
Prometaphase 
metaphase 
anaphase 
telephone 
cytokinesis

Question 13

Metaphase

Answer 13

• Mitosis cannot proceed until chromosomes are properly attached and under tension
• Spindle checkpoint

Question 14

Cohesion complex

Answer 14

Holds sister chromatids together

Question 15

Defects in cohesion can cause disease

Answer 15

• Roberts Syndrome
• Very rare
• Nature Genetics 37:468- 70

Question 16

Defects at spindle checkpoint can cause

Answer 16

aneuploidy

Question 17

Cytokinesis

Answer 17

remaining inter polar miscrotubules form central spindle

contractile ring of actin and myosin filaments in cleavage furrow

Question 18

A cyclin CDK complex is activated by what

Answer 18

activating protein phosphatase which removes a phosphate

Question 19

what is wee1 mutant

Answer 19

it is a form of inhibitory kinase where as CDC 25 is an activating phosphatase

Question 20

what are the two complexes that control events in ell division

Answer 20

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

Question 21

tell me about the pathway of ubiquitylation

Answer 21

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

Question 22

in the G1 phase what ensures only one cycle happens

Answer 22

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

Question 23

what molecule can lead to inhibition of transcription of there is DNA damage

Answer 23

p53 which directs transcription of cdk inhibitors

CHK2 can also be activated which inhibits cdc25

Question 24

what is the action of the anaphase complex

Answer 24

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